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    AV系列结构体之AVCodecContext - 图1

    描述：主要扩展API的结构体

    1. typedef struct AVCodecContext {
    2.     /**
    3.      * information on struct for av_log
    4.      * - set by avcodec_alloc_context3
    5.      */
    6.     const AVClass *av_class;
    7.     int log_level_offset;
    9.     enum AVMediaType codec_type; /* see AVMEDIA_TYPE_xxx */
    10.     const struct AVCodec  *codec;
    11. #if FF_API_CODEC_NAME
    12.     /**
    13.      * @deprecated this field is not used for anything in libavcodec
    14.      */
    15.     attribute_deprecated
    16.     char             codec_name[32];
    17. #endif
    18.     enum AVCodecID     codec_id; /* see AV_CODEC_ID_xxx */
    20.     /**
    21.      * fourcc (LSB first, so "ABCD" -> ('D'<<24) + ('C'<<16) + ('B'<<8) + 'A').
    22.      * This is used to work around some encoder bugs.
    23.      * A demuxer should set this to what is stored in the field used to identify the codec.
    24.      * If there are multiple such fields in a container then the demuxer should choose the one
    25.      * which maximizes the information about the used codec.
    26.      * If the codec tag field in a container is larger than 32 bits then the demuxer should
    27.      * remap the longer ID to 32 bits with a table or other structure. Alternatively a new
    28.      * extra_codec_tag + size could be added but for this a clear advantage must be demonstrated
    29.      * first.
    30.      * - encoding: Set by user, if not then the default based on codec_id will be used.
    31.      * - decoding: Set by user, will be converted to uppercase by libavcodec during init.
    32.      */
    33.     unsigned int codec_tag;
    35. #if FF_API_STREAM_CODEC_TAG
    36.     /**
    37.      * @deprecated this field is unused
    38.      */
    39.     attribute_deprecated
    40.     unsigned int stream_codec_tag;
    41. #endif
    43.     void *priv_data;
    45.     /**
    46.      * Private context used for internal data.
    47.      *
    48.      * Unlike priv_data, this is not codec-specific. It is used in general
    49.      * libavcodec functions.
    50.      */
    51.     struct AVCodecInternal *internal;
    53.     /**
    54.      * Private data of the user, can be used to carry app specific stuff.
    55.      * - encoding: Set by user.
    56.      * - decoding: Set by user.
    57.      */
    58.     void *opaque;
    60.     /**
    61.      * the average bitrate
    62.      * - encoding: Set by user; unused for constant quantizer encoding.
    63.      * - decoding: Set by user, may be overwritten by libavcodec
    64.      *             if this info is available in the stream
    65.      */
    66.     int64_t bit_rate;
    68.     /**
    69.      * number of bits the bitstream is allowed to diverge from the reference.
    70.      *           the reference can be CBR (for CBR pass1) or VBR (for pass2)
    71.      * - encoding: Set by user; unused for constant quantizer encoding.
    72.      * - decoding: unused
    73.      */
    74.     int bit_rate_tolerance;
    76.     /**
    77.      * Global quality for codecs which cannot change it per frame.
    78.      * This should be proportional to MPEG-1/2/4 qscale.
    79.      * - encoding: Set by user.
    80.      * - decoding: unused
    81.      */
    82.     int global_quality;
    84.     /**
    85.      * - encoding: Set by user.
    86.      * - decoding: unused
    87.      */
    88.     int compression_level;
    89. #define FF_COMPRESSION_DEFAULT -1
    91.     /**
    92.      * AV_CODEC_FLAG_*.
    93.      * - encoding: Set by user.
    94.      * - decoding: Set by user.
    95.      */
    96.     int flags;
    98.     /**
    99.      * AV_CODEC_FLAG2_*
    100.      * - encoding: Set by user.
    101.      * - decoding: Set by user.
    102.      */
    103.     int flags2;
    105.     /**
    106.      * some codecs need / can use extradata like Huffman tables.
    107.      * MJPEG: Huffman tables
    108.      * rv10: additional flags
    109.      * MPEG-4: global headers (they can be in the bitstream or here)
    110.      * The allocated memory should be AV_INPUT_BUFFER_PADDING_SIZE bytes larger
    111.      * than extradata_size to avoid problems if it is read with the bitstream reader.
    112.      * The bytewise contents of extradata must not depend on the architecture or CPU endianness.
    113.      * - encoding: Set/allocated/freed by libavcodec.
    114.      * - decoding: Set/allocated/freed by user.
    115.      */
    116.     uint8_t *extradata;
    117.     int extradata_size;
    119.     /**
    120.      * This is the fundamental unit of time (in seconds) in terms
    121.      * of which frame timestamps are represented. For fixed-fps content,
    122.      * timebase should be 1/framerate and timestamp increments should be
    123.      * identically 1.
    124.      * This often, but not always is the inverse of the frame rate or field rate
    125.      * for video. 1/time_base is not the average frame rate if the frame rate is not
    126.      * constant.
    127.      *
    128.      * Like containers, elementary streams also can store timestamps, 1/time_base
    129.      * is the unit in which these timestamps are specified.
    130.      * As example of such codec time base see ISO/IEC 14496-2:2001(E)
    131.      * vop_time_increment_resolution and fixed_vop_rate
    132.      * (fixed_vop_rate == 0 implies that it is different from the framerate)
    133.      *
    134.      * - encoding: MUST be set by user.
    135.      * - decoding: the use of this field for decoding is deprecated.
    136.      *             Use framerate instead.
    137.      */
    138.     AVRational time_base;
    140.     /**
    141.      * For some codecs, the time base is closer to the field rate than the frame rate.
    142.      * Most notably, H.264 and MPEG-2 specify time_base as half of frame duration
    143.      * if no telecine is used ...
    144.      *
    145.      * Set to time_base ticks per frame. Default 1, e.g., H.264/MPEG-2 set it to 2.
    146.      */
    147.     int ticks_per_frame;
    149.     /**
    150.      * Codec delay.
    151.      *
    152.      * Encoding: Number of frames delay there will be from the encoder input to
    153.      *           the decoder output. (we assume the decoder matches the spec)
    154.      * Decoding: Number of frames delay in addition to what a standard decoder
    155.      *           as specified in the spec would produce.
    156.      *
    157.      * Video:
    158.      *   Number of frames the decoded output will be delayed relative to the
    159.      *   encoded input.
    160.      *
    161.      * Audio:
    162.      *   For encoding, this field is unused (see initial_padding).
    163.      *
    164.      *   For decoding, this is the number of samples the decoder needs to
    165.      *   output before the decoder's output is valid. When seeking, you should
    166.      *   start decoding this many samples prior to your desired seek point.
    167.      *
    168.      * - encoding: Set by libavcodec.
    169.      * - decoding: Set by libavcodec.
    170.      */
    171.     int delay;
    174.     /* video only */
    175.     /**
    176.      * picture width / height.
    177.      *
    178.      * @note Those fields may not match the values of the last
    179.      * AVFrame output by avcodec_decode_video2 due frame
    180.      * reordering.
    181.      *
    182.      * - encoding: MUST be set by user.
    183.      * - decoding: May be set by the user before opening the decoder if known e.g.
    184.      *             from the container. Some decoders will require the dimensions
    185.      *             to be set by the caller. During decoding, the decoder may
    186.      *             overwrite those values as required while parsing the data.
    187.      */
    188.     int width, height;
    190.     /**
    191.      * Bitstream width / height, may be different from width/height e.g. when
    192.      * the decoded frame is cropped before being output or lowres is enabled.
    193.      *
    194.      * @note Those field may not match the value of the last
    195.      * AVFrame output by avcodec_receive_frame() due frame
    196.      * reordering.
    197.      *
    198.      * - encoding: unused
    199.      * - decoding: May be set by the user before opening the decoder if known
    200.      *             e.g. from the container. During decoding, the decoder may
    201.      *             overwrite those values as required while parsing the data.
    202.      */
    203.     int coded_width, coded_height;
    205. #if FF_API_ASPECT_EXTENDED
    206. #define FF_ASPECT_EXTENDED 15
    207. #endif
    209.     /**
    210.      * the number of pictures in a group of pictures, or 0 for intra_only
    211.      * - encoding: Set by user.
    212.      * - decoding: unused
    213.      */
    214.     int gop_size;
    216.     /**
    217.      * Pixel format, see AV_PIX_FMT_xxx.
    218.      * May be set by the demuxer if known from headers.
    219.      * May be overridden by the decoder if it knows better.
    220.      *
    221.      * @note This field may not match the value of the last
    222.      * AVFrame output by avcodec_receive_frame() due frame
    223.      * reordering.
    224.      *
    225.      * - encoding: Set by user.
    226.      * - decoding: Set by user if known, overridden by libavcodec while
    227.      *             parsing the data.
    228.      */
    229.     enum AVPixelFormat pix_fmt;
    231. #if FF_API_MOTION_EST
    232.     /**
    233.      * This option does nothing
    234.      * @deprecated use codec private options instead
    235.      */
    236.     attribute_deprecated int me_method;
    237. #endif
    239.     /**
    240.      * If non NULL, 'draw_horiz_band' is called by the libavcodec
    241.      * decoder to draw a horizontal band. It improves cache usage. Not
    242.      * all codecs can do that. You must check the codec capabilities
    243.      * beforehand.
    244.      * When multithreading is used, it may be called from multiple threads
    245.      * at the same time; threads might draw different parts of the same AVFrame,
    246.      * or multiple AVFrames, and there is no guarantee that slices will be drawn
    247.      * in order.
    248.      * The function is also used by hardware acceleration APIs.
    249.      * It is called at least once during frame decoding to pass
    250.      * the data needed for hardware render.
    251.      * In that mode instead of pixel data, AVFrame points to
    252.      * a structure specific to the acceleration API. The application
    253.      * reads the structure and can change some fields to indicate progress
    254.      * or mark state.
    255.      * - encoding: unused
    256.      * - decoding: Set by user.
    257.      * @param height the height of the slice
    258.      * @param y the y position of the slice
    259.      * @param type 1->top field, 2->bottom field, 3->frame
    260.      * @param offset offset into the AVFrame.data from which the slice should be read
    261.      */
    262.     void (*draw_horiz_band)(struct AVCodecContext *s,
    263.                             const AVFrame *src, int offset[AV_NUM_DATA_POINTERS],
    264.                             int y, int type, int height);
    266.     /**
    267.      * callback to negotiate the pixelFormat
    268.      * @param fmt is the list of formats which are supported by the codec,
    269.      * it is terminated by -1 as 0 is a valid format, the formats are ordered by quality.
    270.      * The first is always the native one.
    271.      * @note The callback may be called again immediately if initialization for
    272.      * the selected (hardware-accelerated) pixel format failed.
    273.      * @warning Behavior is undefined if the callback returns a value not
    274.      * in the fmt list of formats.
    275.      * @return the chosen format
    276.      * - encoding: unused
    277.      * - decoding: Set by user, if not set the native format will be chosen.
    278.      */
    279.     enum AVPixelFormat (*get_format)(struct AVCodecContext *s, const enum AVPixelFormat * fmt);
    281.     /**
    282.      * maximum number of B-frames between non-B-frames
    283.      * Note: The output will be delayed by max_b_frames+1 relative to the input.
    284.      * - encoding: Set by user.
    285.      * - decoding: unused
    286.      */
    287.     int max_b_frames;
    289.     /**
    290.      * qscale factor between IP and B-frames
    291.      * If > 0 then the last P-frame quantizer will be used (q= lastp_q*factor+offset).
    292.      * If < 0 then normal ratecontrol will be done (q= -normal_q*factor+offset).
    293.      * - encoding: Set by user.
    294.      * - decoding: unused
    295.      */
    296.     float b_quant_factor;
    298. #if FF_API_RC_STRATEGY
    299.     /** @deprecated use codec private option instead */
    300.     attribute_deprecated int rc_strategy;
    301. #define FF_RC_STRATEGY_XVID 1
    302. #endif
    304. #if FF_API_PRIVATE_OPT
    305.     /** @deprecated use encoder private options instead */
    306.     attribute_deprecated
    307.     int b_frame_strategy;
    308. #endif
    310.     /**
    311.      * qscale offset between IP and B-frames
    312.      * - encoding: Set by user.
    313.      * - decoding: unused
    314.      */
    315.     float b_quant_offset;
    317.     /**
    318.      * Size of the frame reordering buffer in the decoder.
    319.      * For MPEG-2 it is 1 IPB or 0 low delay IP.
    320.      * - encoding: Set by libavcodec.
    321.      * - decoding: Set by libavcodec.
    322.      */
    323.     int has_b_frames;
    325. #if FF_API_PRIVATE_OPT
    326.     /** @deprecated use encoder private options instead */
    327.     attribute_deprecated
    328.     int mpeg_quant;
    329. #endif
    331.     /**
    332.      * qscale factor between P- and I-frames
    333.      * If > 0 then the last P-frame quantizer will be used (q = lastp_q * factor + offset).
    334.      * If < 0 then normal ratecontrol will be done (q= -normal_q*factor+offset).
    335.      * - encoding: Set by user.
    336.      * - decoding: unused
    337.      */
    338.     float i_quant_factor;
    340.     /**
    341.      * qscale offset between P and I-frames
    342.      * - encoding: Set by user.
    343.      * - decoding: unused
    344.      */
    345.     float i_quant_offset;
    347.     /**
    348.      * luminance masking (0-> disabled)
    349.      * - encoding: Set by user.
    350.      * - decoding: unused
    351.      */
    352.     float lumi_masking;
    354.     /**
    355.      * temporary complexity masking (0-> disabled)
    356.      * - encoding: Set by user.
    357.      * - decoding: unused
    358.      */
    359.     float temporal_cplx_masking;
    361.     /**
    362.      * spatial complexity masking (0-> disabled)
    363.      * - encoding: Set by user.
    364.      * - decoding: unused
    365.      */
    366.     float spatial_cplx_masking;
    368.     /**
    369.      * p block masking (0-> disabled)
    370.      * - encoding: Set by user.
    371.      * - decoding: unused
    372.      */
    373.     float p_masking;
    375.     /**
    376.      * darkness masking (0-> disabled)
    377.      * - encoding: Set by user.
    378.      * - decoding: unused
    379.      */
    380.     float dark_masking;
    382.     /**
    383.      * slice count
    384.      * - encoding: Set by libavcodec.
    385.      * - decoding: Set by user (or 0).
    386.      */
    387.     int slice_count;
    389. #if FF_API_PRIVATE_OPT
    390.     /** @deprecated use encoder private options instead */
    391.     attribute_deprecated
    392.      int prediction_method;
    393. #define FF_PRED_LEFT   0
    394. #define FF_PRED_PLANE  1
    395. #define FF_PRED_MEDIAN 2
    396. #endif
    398.     /**
    399.      * slice offsets in the frame in bytes
    400.      * - encoding: Set/allocated by libavcodec.
    401.      * - decoding: Set/allocated by user (or NULL).
    402.      */
    403.     int *slice_offset;
    405.     /**
    406.      * sample aspect ratio (0 if unknown)
    407.      * That is the width of a pixel divided by the height of the pixel.
    408.      * Numerator and denominator must be relatively prime and smaller than 256 for some video standards.
    409.      * - encoding: Set by user.
    410.      * - decoding: Set by libavcodec.
    411.      */
    412.     AVRational sample_aspect_ratio;
    414.     /**
    415.      * motion estimation comparison function
    416.      * - encoding: Set by user.
    417.      * - decoding: unused
    418.      */
    419.     int me_cmp;
    420.     /**
    421.      * subpixel motion estimation comparison function
    422.      * - encoding: Set by user.
    423.      * - decoding: unused
    424.      */
    425.     int me_sub_cmp;
    426.     /**
    427.      * macroblock comparison function (not supported yet)
    428.      * - encoding: Set by user.
    429.      * - decoding: unused
    430.      */
    431.     int mb_cmp;
    432.     /**
    433.      * interlaced DCT comparison function
    434.      * - encoding: Set by user.
    435.      * - decoding: unused
    436.      */
    437.     int ildct_cmp;
    438. #define FF_CMP_SAD    0
    439. #define FF_CMP_SSE    1
    440. #define FF_CMP_SATD   2
    441. #define FF_CMP_DCT    3
    442. #define FF_CMP_PSNR   4
    443. #define FF_CMP_BIT    5
    444. #define FF_CMP_RD     6
    445. #define FF_CMP_ZERO   7
    446. #define FF_CMP_VSAD   8
    447. #define FF_CMP_VSSE   9
    448. #define FF_CMP_NSSE   10
    449. #define FF_CMP_W53    11
    450. #define FF_CMP_W97    12
    451. #define FF_CMP_DCTMAX 13
    452. #define FF_CMP_DCT264 14
    453. #define FF_CMP_CHROMA 256
    455.     /**
    456.      * ME diamond size & shape
    457.      * - encoding: Set by user.
    458.      * - decoding: unused
    459.      */
    460.     int dia_size;
    462.     /**
    463.      * amount of previous MV predictors (2a+1 x 2a+1 square)
    464.      * - encoding: Set by user.
    465.      * - decoding: unused
    466.      */
    467.     int last_predictor_count;
    469. #if FF_API_PRIVATE_OPT
    470.     /** @deprecated use encoder private options instead */
    471.     attribute_deprecated
    472.     int pre_me;
    473. #endif
    475.     /**
    476.      * motion estimation prepass comparison function
    477.      * - encoding: Set by user.
    478.      * - decoding: unused
    479.      */
    480.     int me_pre_cmp;
    482.     /**
    483.      * ME prepass diamond size & shape
    484.      * - encoding: Set by user.
    485.      * - decoding: unused
    486.      */
    487.     int pre_dia_size;
    489.     /**
    490.      * subpel ME quality
    491.      * - encoding: Set by user.
    492.      * - decoding: unused
    493.      */
    494.     int me_subpel_quality;
    496. #if FF_API_AFD
    497.     /**
    498.      * DTG active format information (additional aspect ratio
    499.      * information only used in DVB MPEG-2 transport streams)
    500.      * 0 if not set.
    501.      *
    502.      * - encoding: unused
    503.      * - decoding: Set by decoder.
    504.      * @deprecated Deprecated in favor of AVSideData
    505.      */
    506.     attribute_deprecated int dtg_active_format;
    507. #define FF_DTG_AFD_SAME         8
    508. #define FF_DTG_AFD_4_3          9
    509. #define FF_DTG_AFD_16_9         10
    510. #define FF_DTG_AFD_14_9         11
    511. #define FF_DTG_AFD_4_3_SP_14_9  13
    512. #define FF_DTG_AFD_16_9_SP_14_9 14
    513. #define FF_DTG_AFD_SP_4_3       15
    514. #endif /* FF_API_AFD */
    516.     /**
    517.      * maximum motion estimation search range in subpel units
    518.      * If 0 then no limit.
    519.      *
    520.      * - encoding: Set by user.
    521.      * - decoding: unused
    522.      */
    523.     int me_range;
    525. #if FF_API_QUANT_BIAS
    526.     /**
    527.      * @deprecated use encoder private option instead
    528.      */
    529.     attribute_deprecated int intra_quant_bias;
    530. #define FF_DEFAULT_QUANT_BIAS 999999
    532.     /**
    533.      * @deprecated use encoder private option instead
    534.      */
    535.     attribute_deprecated int inter_quant_bias;
    536. #endif
    538.     /**
    539.      * slice flags
    540.      * - encoding: unused
    541.      * - decoding: Set by user.
    542.      */
    543.     int slice_flags;
    544. #define SLICE_FLAG_CODED_ORDER    0x0001 ///< draw_horiz_band() is called in coded order instead of display
    545. #define SLICE_FLAG_ALLOW_FIELD    0x0002 ///< allow draw_horiz_band() with field slices (MPEG-2 field pics)
    546. #define SLICE_FLAG_ALLOW_PLANE    0x0004 ///< allow draw_horiz_band() with 1 component at a time (SVQ1)
    548. #if FF_API_XVMC
    549.     /**
    550.      * XVideo Motion Acceleration
    551.      * - encoding: forbidden
    552.      * - decoding: set by decoder
    553.      * @deprecated XvMC doesn't need it anymore.
    554.      */
    555.     attribute_deprecated int xvmc_acceleration;
    556. #endif /* FF_API_XVMC */
    558.     /**
    559.      * macroblock decision mode
    560.      * - encoding: Set by user.
    561.      * - decoding: unused
    562.      */
    563.     int mb_decision;
    564. #define FF_MB_DECISION_SIMPLE 0        ///< uses mb_cmp
    565. #define FF_MB_DECISION_BITS   1        ///< chooses the one which needs the fewest bits
    566. #define FF_MB_DECISION_RD     2        ///< rate distortion
    568.     /**
    569.      * custom intra quantization matrix
    570.      * - encoding: Set by user, can be NULL.
    571.      * - decoding: Set by libavcodec.
    572.      */
    573.     uint16_t *intra_matrix;
    575.     /**
    576.      * custom inter quantization matrix
    577.      * - encoding: Set by user, can be NULL.
    578.      * - decoding: Set by libavcodec.
    579.      */
    580.     uint16_t *inter_matrix;
    582. #if FF_API_PRIVATE_OPT
    583.     /** @deprecated use encoder private options instead */
    584.     attribute_deprecated
    585.     int scenechange_threshold;
    587.     /** @deprecated use encoder private options instead */
    588.     attribute_deprecated
    589.     int noise_reduction;
    590. #endif
    592. #if FF_API_MPV_OPT
    593.     /**
    594.      * @deprecated this field is unused
    595.      */
    596.     attribute_deprecated
    597.     int me_threshold;
    599.     /**
    600.      * @deprecated this field is unused
    601.      */
    602.     attribute_deprecated
    603.     int mb_threshold;
    604. #endif
    606.     /**
    607.      * precision of the intra DC coefficient - 8
    608.      * - encoding: Set by user.
    609.      * - decoding: Set by libavcodec
    610.      */
    611.     int intra_dc_precision;
    613.     /**
    614.      * Number of macroblock rows at the top which are skipped.
    615.      * - encoding: unused
    616.      * - decoding: Set by user.
    617.      */
    618.     int skip_top;
    620.     /**
    621.      * Number of macroblock rows at the bottom which are skipped.
    622.      * - encoding: unused
    623.      * - decoding: Set by user.
    624.      */
    625.     int skip_bottom;
    627. #if FF_API_MPV_OPT
    628.     /**
    629.      * @deprecated use encoder private options instead
    630.      */
    631.     attribute_deprecated
    632.     float border_masking;
    633. #endif
    635.     /**
    636.      * minimum MB Lagrange multiplier
    637.      * - encoding: Set by user.
    638.      * - decoding: unused
    639.      */
    640.     int mb_lmin;
    642.     /**
    643.      * maximum MB Lagrange multiplier
    644.      * - encoding: Set by user.
    645.      * - decoding: unused
    646.      */
    647.     int mb_lmax;
    649. #if FF_API_PRIVATE_OPT
    650.     /**
    651.      * @deprecated use encoder private options instead
    652.      */
    653.     attribute_deprecated
    654.     int me_penalty_compensation;
    655. #endif
    657.     /**
    658.      * - encoding: Set by user.
    659.      * - decoding: unused
    660.      */
    661.     int bidir_refine;
    663. #if FF_API_PRIVATE_OPT
    664.     /** @deprecated use encoder private options instead */
    665.     attribute_deprecated
    666.     int brd_scale;
    667. #endif
    669.     /**
    670.      * minimum GOP size
    671.      * - encoding: Set by user.
    672.      * - decoding: unused
    673.      */
    674.     int keyint_min;
    676.     /**
    677.      * number of reference frames
    678.      * - encoding: Set by user.
    679.      * - decoding: Set by lavc.
    680.      */
    681.     int refs;
    683. #if FF_API_PRIVATE_OPT
    684.     /** @deprecated use encoder private options instead */
    685.     attribute_deprecated
    686.     int chromaoffset;
    687. #endif
    689. #if FF_API_UNUSED_MEMBERS
    690.     /**
    691.      * Multiplied by qscale for each frame and added to scene_change_score.
    692.      * - encoding: Set by user.
    693.      * - decoding: unused
    694.      */
    695.     attribute_deprecated int scenechange_factor;
    696. #endif
    698.     /**
    699.      * Note: Value depends upon the compare function used for fullpel ME.
    700.      * - encoding: Set by user.
    701.      * - decoding: unused
    702.      */
    703.     int mv0_threshold;
    705. #if FF_API_PRIVATE_OPT
    706.     /** @deprecated use encoder private options instead */
    707.     attribute_deprecated
    708.     int b_sensitivity;
    709. #endif
    711.     /**
    712.      * Chromaticity coordinates of the source primaries.
    713.      * - encoding: Set by user
    714.      * - decoding: Set by libavcodec
    715.      */
    716.     enum AVColorPrimaries color_primaries;
    718.     /**
    719.      * Color Transfer Characteristic.
    720.      * - encoding: Set by user
    721.      * - decoding: Set by libavcodec
    722.      */
    723.     enum AVColorTransferCharacteristic color_trc;
    725.     /**
    726.      * YUV colorspace type.
    727.      * - encoding: Set by user
    728.      * - decoding: Set by libavcodec
    729.      */
    730.     enum AVColorSpace colorspace;
    732.     /**
    733.      * MPEG vs JPEG YUV range.
    734.      * - encoding: Set by user
    735.      * - decoding: Set by libavcodec
    736.      */
    737.     enum AVColorRange color_range;
    739.     /**
    740.      * This defines the location of chroma samples.
    741.      * - encoding: Set by user
    742.      * - decoding: Set by libavcodec
    743.      */
    744.     enum AVChromaLocation chroma_sample_location;
    746.     /**
    747.      * Number of slices.
    748.      * Indicates number of picture subdivisions. Used for parallelized
    749.      * decoding.
    750.      * - encoding: Set by user
    751.      * - decoding: unused
    752.      */
    753.     int slices;
    755.     /** Field order
    756.      * - encoding: set by libavcodec
    757.      * - decoding: Set by user.
    758.      */
    759.     enum AVFieldOrder field_order;
    761.     /* audio only */
    762.     int sample_rate; ///< samples per second
    763.     int channels;    ///< number of audio channels
    765.     /**
    766.      * audio sample format
    767.      * - encoding: Set by user.
    768.      * - decoding: Set by libavcodec.
    769.      */
    770.     enum AVSampleFormat sample_fmt;  ///< sample format
    772.     /* The following data should not be initialized. */
    773.     /**
    774.      * Number of samples per channel in an audio frame.
    775.      *
    776.      * - encoding: set by libavcodec in avcodec_open2(). Each submitted frame
    777.      *   except the last must contain exactly frame_size samples per channel.
    778.      *   May be 0 when the codec has AV_CODEC_CAP_VARIABLE_FRAME_SIZE set, then the
    779.      *   frame size is not restricted.
    780.      * - decoding: may be set by some decoders to indicate constant frame size
    781.      */
    782.     int frame_size;
    784.     /**
    785.      * Frame counter, set by libavcodec.
    786.      *
    787.      * - decoding: total number of frames returned from the decoder so far.
    788.      * - encoding: total number of frames passed to the encoder so far.
    789.      *
    790.      *   @note the counter is not incremented if encoding/decoding resulted in
    791.      *   an error.
    792.      */
    793.     int frame_number;
    795.     /**
    796.      * number of bytes per packet if constant and known or 0
    797.      * Used by some WAV based audio codecs.
    798.      */
    799.     int block_align;
    801.     /**
    802.      * Audio cutoff bandwidth (0 means "automatic")
    803.      * - encoding: Set by user.
    804.      * - decoding: unused
    805.      */
    806.     int cutoff;
    808.     /**
    809.      * Audio channel layout.
    810.      * - encoding: set by user.
    811.      * - decoding: set by user, may be overwritten by libavcodec.
    812.      */
    813.     uint64_t channel_layout;
    815.     /**
    816.      * Request decoder to use this channel layout if it can (0 for default)
    817.      * - encoding: unused
    818.      * - decoding: Set by user.
    819.      */
    820.     uint64_t request_channel_layout;
    822.     /**
    823.      * Type of service that the audio stream conveys.
    824.      * - encoding: Set by user.
    825.      * - decoding: Set by libavcodec.
    826.      */
    827.     enum AVAudioServiceType audio_service_type;
    829.     /**
    830.      * desired sample format
    831.      * - encoding: Not used.
    832.      * - decoding: Set by user.
    833.      * Decoder will decode to this format if it can.
    834.      */
    835.     enum AVSampleFormat request_sample_fmt;
    837.     /**
    838.      * This callback is called at the beginning of each frame to get data
    839.      * buffer(s) for it. There may be one contiguous buffer for all the data or
    840.      * there may be a buffer per each data plane or anything in between. What
    841.      * this means is, you may set however many entries in buf[] you feel necessary.
    842.      * Each buffer must be reference-counted using the AVBuffer API (see description
    843.      * of buf[] below).
    844.      *
    845.      * The following fields will be set in the frame before this callback is
    846.      * called:
    847.      * - format
    848.      * - width, height (video only)
    849.      * - sample_rate, channel_layout, nb_samples (audio only)
    850.      * Their values may differ from the corresponding values in
    851.      * AVCodecContext. This callback must use the frame values, not the codec
    852.      * context values, to calculate the required buffer size.
    853.      *
    854.      * This callback must fill the following fields in the frame:
    855.      * - data[]
    856.      * - linesize[]
    857.      * - extended_data:
    858.      *   * if the data is planar audio with more than 8 channels, then this
    859.      *     callback must allocate and fill extended_data to contain all pointers
    860.      *     to all data planes. data[] must hold as many pointers as it can.
    861.      *     extended_data must be allocated with av_malloc() and will be freed in
    862.      *     av_frame_unref().
    863.      *   * otherwise extended_data must point to data
    864.      * - buf[] must contain one or more pointers to AVBufferRef structures. Each of
    865.      *   the frame's data and extended_data pointers must be contained in these. That
    866.      *   is, one AVBufferRef for each allocated chunk of memory, not necessarily one
    867.      *   AVBufferRef per data[] entry. See: av_buffer_create(), av_buffer_alloc(),
    868.      *   and av_buffer_ref().
    869.      * - extended_buf and nb_extended_buf must be allocated with av_malloc() by
    870.      *   this callback and filled with the extra buffers if there are more
    871.      *   buffers than buf[] can hold. extended_buf will be freed in
    872.      *   av_frame_unref().
    873.      *
    874.      * If AV_CODEC_CAP_DR1 is not set then get_buffer2() must call
    875.      * avcodec_default_get_buffer2() instead of providing buffers allocated by
    876.      * some other means.
    877.      *
    878.      * Each data plane must be aligned to the maximum required by the target
    879.      * CPU.
    880.      *
    881.      * @see avcodec_default_get_buffer2()
    882.      *
    883.      * Video:
    884.      *
    885.      * If AV_GET_BUFFER_FLAG_REF is set in flags then the frame may be reused
    886.      * (read and/or written to if it is writable) later by libavcodec.
    887.      *
    888.      * avcodec_align_dimensions2() should be used to find the required width and
    889.      * height, as they normally need to be rounded up to the next multiple of 16.
    890.      *
    891.      * Some decoders do not support linesizes changing between frames.
    892.      *
    893.      * If frame multithreading is used and thread_safe_callbacks is set,
    894.      * this callback may be called from a different thread, but not from more
    895.      * than one at once. Does not need to be reentrant.
    896.      *
    897.      * @see avcodec_align_dimensions2()
    898.      *
    899.      * Audio:
    900.      *
    901.      * Decoders request a buffer of a particular size by setting
    902.      * AVFrame.nb_samples prior to calling get_buffer2(). The decoder may,
    903.      * however, utilize only part of the buffer by setting AVFrame.nb_samples
    904.      * to a smaller value in the output frame.
    905.      *
    906.      * As a convenience, av_samples_get_buffer_size() and
    907.      * av_samples_fill_arrays() in libavutil may be used by custom get_buffer2()
    908.      * functions to find the required data size and to fill data pointers and
    909.      * linesize. In AVFrame.linesize, only linesize[0] may be set for audio
    910.      * since all planes must be the same size.
    911.      *
    912.      * @see av_samples_get_buffer_size(), av_samples_fill_arrays()
    913.      *
    914.      * - encoding: unused
    915.      * - decoding: Set by libavcodec, user can override.
    916.      */
    917.     int (*get_buffer2)(struct AVCodecContext *s, AVFrame *frame, int flags);
    919.     /**
    920.      * If non-zero, the decoded audio and video frames returned from
    921.      * avcodec_decode_video2() and avcodec_decode_audio4() are reference-counted
    922.      * and are valid indefinitely. The caller must free them with
    923.      * av_frame_unref() when they are not needed anymore.
    924.      * Otherwise, the decoded frames must not be freed by the caller and are
    925.      * only valid until the next decode call.
    926.      *
    927.      * This is always automatically enabled if avcodec_receive_frame() is used.
    928.      *
    929.      * - encoding: unused
    930.      * - decoding: set by the caller before avcodec_open2().
    931.      */
    932.     int refcounted_frames;
    934.     /* - encoding parameters */
    935.     float qcompress;  ///< amount of qscale change between easy & hard scenes (0.0-1.0)
    936.     float qblur;      ///< amount of qscale smoothing over time (0.0-1.0)
    938.     /**
    939.      * minimum quantizer
    940.      * - encoding: Set by user.
    941.      * - decoding: unused
    942.      */
    943.     int qmin;
    945.     /**
    946.      * maximum quantizer
    947.      * - encoding: Set by user.
    948.      * - decoding: unused
    949.      */
    950.     int qmax;
    952.     /**
    953.      * maximum quantizer difference between frames
    954.      * - encoding: Set by user.
    955.      * - decoding: unused
    956.      */
    957.     int max_qdiff;
    959. #if FF_API_MPV_OPT
    960.     /**
    961.      * @deprecated use encoder private options instead
    962.      */
    963.     attribute_deprecated
    964.     float rc_qsquish;
    966.     attribute_deprecated
    967.     float rc_qmod_amp;
    968.     attribute_deprecated
    969.     int rc_qmod_freq;
    970. #endif
    972.     /**
    973.      * decoder bitstream buffer size
    974.      * - encoding: Set by user.
    975.      * - decoding: unused
    976.      */
    977.     int rc_buffer_size;
    979.     /**
    980.      * ratecontrol override, see RcOverride
    981.      * - encoding: Allocated/set/freed by user.
    982.      * - decoding: unused
    983.      */
    984.     int rc_override_count;
    985.     RcOverride *rc_override;
    987. #if FF_API_MPV_OPT
    988.     /**
    989.      * @deprecated use encoder private options instead
    990.      */
    991.     attribute_deprecated
    992.     const char *rc_eq;
    993. #endif
    995.     /**
    996.      * maximum bitrate
    997.      * - encoding: Set by user.
    998.      * - decoding: Set by user, may be overwritten by libavcodec.
    999.      */
    1000.     int64_t rc_max_rate;
    1002.     /**
    1003.      * minimum bitrate
    1004.      * - encoding: Set by user.
    1005.      * - decoding: unused
    1006.      */
    1007.     int64_t rc_min_rate;
    1009. #if FF_API_MPV_OPT
    1010.     /**
    1011.      * @deprecated use encoder private options instead
    1012.      */
    1013.     attribute_deprecated
    1014.     float rc_buffer_aggressivity;
    1016.     attribute_deprecated
    1017.     float rc_initial_cplx;
    1018. #endif
    1020.     /**
    1021.      * Ratecontrol attempt to use, at maximum, <value> of what can be used without an underflow.
    1022.      * - encoding: Set by user.
    1023.      * - decoding: unused.
    1024.      */
    1025.     float rc_max_available_vbv_use;
    1027.     /**
    1028.      * Ratecontrol attempt to use, at least, <value> times the amount needed to prevent a vbv overflow.
    1029.      * - encoding: Set by user.
    1030.      * - decoding: unused.
    1031.      */
    1032.     float rc_min_vbv_overflow_use;
    1034.     /**
    1035.      * Number of bits which should be loaded into the rc buffer before decoding starts.
    1036.      * - encoding: Set by user.
    1037.      * - decoding: unused
    1038.      */
    1039.     int rc_initial_buffer_occupancy;
    1041. #if FF_API_CODER_TYPE
    1042. #define FF_CODER_TYPE_VLC       0
    1043. #define FF_CODER_TYPE_AC        1
    1044. #define FF_CODER_TYPE_RAW       2
    1045. #define FF_CODER_TYPE_RLE       3
    1046. #if FF_API_UNUSED_MEMBERS
    1047. #define FF_CODER_TYPE_DEFLATE   4
    1048. #endif /* FF_API_UNUSED_MEMBERS */
    1049.     /**
    1050.      * @deprecated use encoder private options instead
    1051.      */
    1052.     attribute_deprecated
    1053.     int coder_type;
    1054. #endif /* FF_API_CODER_TYPE */
    1056. #if FF_API_PRIVATE_OPT
    1057.     /** @deprecated use encoder private options instead */
    1058.     attribute_deprecated
    1059.     int context_model;
    1060. #endif
    1062. #if FF_API_MPV_OPT
    1063.     /**
    1064.      * @deprecated use encoder private options instead
    1065.      */
    1066.     attribute_deprecated
    1067.     int lmin;
    1069.     /**
    1070.      * @deprecated use encoder private options instead
    1071.      */
    1072.     attribute_deprecated
    1073.     int lmax;
    1074. #endif
    1076. #if FF_API_PRIVATE_OPT
    1077.     /** @deprecated use encoder private options instead */
    1078.     attribute_deprecated
    1079.     int frame_skip_threshold;
    1081.     /** @deprecated use encoder private options instead */
    1082.     attribute_deprecated
    1083.     int frame_skip_factor;
    1085.     /** @deprecated use encoder private options instead */
    1086.     attribute_deprecated
    1087.     int frame_skip_exp;
    1089.     /** @deprecated use encoder private options instead */
    1090.     attribute_deprecated
    1091.     int frame_skip_cmp;
    1092. #endif /* FF_API_PRIVATE_OPT */
    1094.     /**
    1095.      * trellis RD quantization
    1096.      * - encoding: Set by user.
    1097.      * - decoding: unused
    1098.      */
    1099.     int trellis;
    1101. #if FF_API_PRIVATE_OPT
    1102.     /** @deprecated use encoder private options instead */
    1103.     attribute_deprecated
    1104.     int min_prediction_order;
    1106.     /** @deprecated use encoder private options instead */
    1107.     attribute_deprecated
    1108.     int max_prediction_order;
    1110.     /** @deprecated use encoder private options instead */
    1111.     attribute_deprecated
    1112.     int64_t timecode_frame_start;
    1113. #endif
    1115. #if FF_API_RTP_CALLBACK
    1116.     /**
    1117.      * @deprecated unused
    1118.      */
    1119.     /* The RTP callback: This function is called    */
    1120.     /* every time the encoder has a packet to send. */
    1121.     /* It depends on the encoder if the data starts */
    1122.     /* with a Start Code (it should). H.263 does.   */
    1123.     /* mb_nb contains the number of macroblocks     */
    1124.     /* encoded in the RTP payload.                  */
    1125.     attribute_deprecated
    1126.     void (*rtp_callback)(struct AVCodecContext *avctx, void *data, int size, int mb_nb);
    1127. #endif
    1129. #if FF_API_PRIVATE_OPT
    1130.     /** @deprecated use encoder private options instead */
    1131.     attribute_deprecated
    1132.     int rtp_payload_size;   /* The size of the RTP payload: the coder will  */
    1133.                             /* do its best to deliver a chunk with size     */
    1134.                             /* below rtp_payload_size, the chunk will start */
    1135.                             /* with a start code on some codecs like H.263. */
    1136.                             /* This doesn't take account of any particular  */
    1137.                             /* headers inside the transmitted RTP payload.  */
    1138. #endif
    1140. #if FF_API_STAT_BITS
    1141.     /* statistics, used for 2-pass encoding */
    1142.     attribute_deprecated
    1143.     int mv_bits;
    1144.     attribute_deprecated
    1145.     int header_bits;
    1146.     attribute_deprecated
    1147.     int i_tex_bits;
    1148.     attribute_deprecated
    1149.     int p_tex_bits;
    1150.     attribute_deprecated
    1151.     int i_count;
    1152.     attribute_deprecated
    1153.     int p_count;
    1154.     attribute_deprecated
    1155.     int skip_count;
    1156.     attribute_deprecated
    1157.     int misc_bits;
    1159.     /** @deprecated this field is unused */
    1160.     attribute_deprecated
    1161.     int frame_bits;
    1162. #endif
    1164.     /**
    1165.      * pass1 encoding statistics output buffer
    1166.      * - encoding: Set by libavcodec.
    1167.      * - decoding: unused
    1168.      */
    1169.     char *stats_out;
    1171.     /**
    1172.      * pass2 encoding statistics input buffer
    1173.      * Concatenated stuff from stats_out of pass1 should be placed here.
    1174.      * - encoding: Allocated/set/freed by user.
    1175.      * - decoding: unused
    1176.      */
    1177.     char *stats_in;
    1179.     /**
    1180.      * Work around bugs in encoders which sometimes cannot be detected automatically.
    1181.      * - encoding: Set by user
    1182.      * - decoding: Set by user
    1183.      */
    1184.     int workaround_bugs;
    1185. #define FF_BUG_AUTODETECT       1  ///< autodetection
    1186. #if FF_API_OLD_MSMPEG4
    1187. #define FF_BUG_OLD_MSMPEG4      2
    1188. #endif
    1189. #define FF_BUG_XVID_ILACE       4
    1190. #define FF_BUG_UMP4             8
    1191. #define FF_BUG_NO_PADDING       16
    1192. #define FF_BUG_AMV              32
    1193. #if FF_API_AC_VLC
    1194. #define FF_BUG_AC_VLC           0  ///< Will be removed, libavcodec can now handle these non-compliant files by default.
    1195. #endif
    1196. #define FF_BUG_QPEL_CHROMA      64
    1197. #define FF_BUG_STD_QPEL         128
    1198. #define FF_BUG_QPEL_CHROMA2     256
    1199. #define FF_BUG_DIRECT_BLOCKSIZE 512
    1200. #define FF_BUG_EDGE             1024
    1201. #define FF_BUG_HPEL_CHROMA      2048
    1202. #define FF_BUG_DC_CLIP          4096
    1203. #define FF_BUG_MS               8192 ///< Work around various bugs in Microsoft's broken decoders.
    1204. #define FF_BUG_TRUNCATED       16384
    1206.     /**
    1207.      * strictly follow the standard (MPEG-4, ...).
    1208.      * - encoding: Set by user.
    1209.      * - decoding: Set by user.
    1210.      * Setting this to STRICT or higher means the encoder and decoder will
    1211.      * generally do stupid things, whereas setting it to unofficial or lower
    1212.      * will mean the encoder might produce output that is not supported by all
    1213.      * spec-compliant decoders. Decoders don't differentiate between normal,
    1214.      * unofficial and experimental (that is, they always try to decode things
    1215.      * when they can) unless they are explicitly asked to behave stupidly
    1216.      * (=strictly conform to the specs)
    1217.      */
    1218.     int strict_std_compliance;
    1219. #define FF_COMPLIANCE_VERY_STRICT   2 ///< Strictly conform to an older more strict version of the spec or reference software.
    1220. #define FF_COMPLIANCE_STRICT        1 ///< Strictly conform to all the things in the spec no matter what consequences.
    1221. #define FF_COMPLIANCE_NORMAL        0
    1222. #define FF_COMPLIANCE_UNOFFICIAL   -1 ///< Allow unofficial extensions
    1223. #define FF_COMPLIANCE_EXPERIMENTAL -2 ///< Allow nonstandardized experimental things.
    1225.     /**
    1226.      * error concealment flags
    1227.      * - encoding: unused
    1228.      * - decoding: Set by user.
    1229.      */
    1230.     int error_concealment;
    1231. #define FF_EC_GUESS_MVS   1
    1232. #define FF_EC_DEBLOCK     2
    1233. #define FF_EC_FAVOR_INTER 256
    1235.     /**
    1236.      * debug
    1237.      * - encoding: Set by user.
    1238.      * - decoding: Set by user.
    1239.      */
    1240.     int debug;
    1241. #define FF_DEBUG_PICT_INFO   1
    1242. #define FF_DEBUG_RC          2
    1243. #define FF_DEBUG_BITSTREAM   4
    1244. #define FF_DEBUG_MB_TYPE     8
    1245. #define FF_DEBUG_QP          16
    1246. #if FF_API_DEBUG_MV
    1247. /**
    1248.  * @deprecated this option does nothing
    1249.  */
    1250. #define FF_DEBUG_MV          32
    1251. #endif
    1252. #define FF_DEBUG_DCT_COEFF   0x00000040
    1253. #define FF_DEBUG_SKIP        0x00000080
    1254. #define FF_DEBUG_STARTCODE   0x00000100
    1255. #if FF_API_UNUSED_MEMBERS
    1256. #define FF_DEBUG_PTS         0x00000200
    1257. #endif /* FF_API_UNUSED_MEMBERS */
    1258. #define FF_DEBUG_ER          0x00000400
    1259. #define FF_DEBUG_MMCO        0x00000800
    1260. #define FF_DEBUG_BUGS        0x00001000
    1261. #if FF_API_DEBUG_MV
    1262. #define FF_DEBUG_VIS_QP      0x00002000 ///< only access through AVOptions from outside libavcodec
    1263. #define FF_DEBUG_VIS_MB_TYPE 0x00004000 ///< only access through AVOptions from outside libavcodec
    1264. #endif
    1265. #define FF_DEBUG_BUFFERS     0x00008000
    1266. #define FF_DEBUG_THREADS     0x00010000
    1267. #define FF_DEBUG_GREEN_MD    0x00800000
    1268. #define FF_DEBUG_NOMC        0x01000000
    1270. #if FF_API_DEBUG_MV
    1271.     /**
    1272.      * debug
    1273.      * Code outside libavcodec should access this field using AVOptions
    1274.      * - encoding: Set by user.
    1275.      * - decoding: Set by user.
    1276.      */
    1277.     int debug_mv;
    1278. #define FF_DEBUG_VIS_MV_P_FOR  0x00000001 // visualize forward predicted MVs of P-frames
    1279. #define FF_DEBUG_VIS_MV_B_FOR  0x00000002 // visualize forward predicted MVs of B-frames
    1280. #define FF_DEBUG_VIS_MV_B_BACK 0x00000004 // visualize backward predicted MVs of B-frames
    1281. #endif
    1283.     /**
    1284.      * Error recognition; may misdetect some more or less valid parts as errors.
    1285.      * - encoding: unused
    1286.      * - decoding: Set by user.
    1287.      */
    1288.     int err_recognition;
    1290. /**
    1291.  * Verify checksums embedded in the bitstream (could be of either encoded or
    1292.  * decoded data, depending on the codec) and print an error message on mismatch.
    1293.  * If AV_EF_EXPLODE is also set, a mismatching checksum will result in the
    1294.  * decoder returning an error.
    1295.  */
    1296. #define AV_EF_CRCCHECK  (1<<0)
    1297. #define AV_EF_BITSTREAM (1<<1)          ///< detect bitstream specification deviations
    1298. #define AV_EF_BUFFER    (1<<2)          ///< detect improper bitstream length
    1299. #define AV_EF_EXPLODE   (1<<3)          ///< abort decoding on minor error detection
    1301. #define AV_EF_IGNORE_ERR (1<<15)        ///< ignore errors and continue
    1302. #define AV_EF_CAREFUL    (1<<16)        ///< consider things that violate the spec, are fast to calculate and have not been seen in the wild as errors
    1303. #define AV_EF_COMPLIANT  (1<<17)        ///< consider all spec non compliances as errors
    1304. #define AV_EF_AGGRESSIVE (1<<18)        ///< consider things that a sane encoder should not do as an error
    1307.     /**
    1308.      * opaque 64-bit number (generally a PTS) that will be reordered and
    1309.      * output in AVFrame.reordered_opaque
    1310.      * - encoding: unused
    1311.      * - decoding: Set by user.
    1312.      */
    1313.     int64_t reordered_opaque;
    1315.     /**
    1316.      * Hardware accelerator in use
    1317.      * - encoding: unused.
    1318.      * - decoding: Set by libavcodec
    1319.      */
    1320.     struct AVHWAccel *hwaccel;
    1322.     /**
    1323.      * Hardware accelerator context.
    1324.      * For some hardware accelerators, a global context needs to be
    1325.      * provided by the user. In that case, this holds display-dependent
    1326.      * data FFmpeg cannot instantiate itself. Please refer to the
    1327.      * FFmpeg HW accelerator documentation to know how to fill this
    1328.      * is. e.g. for VA API, this is a struct vaapi_context.
    1329.      * - encoding: unused
    1330.      * - decoding: Set by user
    1331.      */
    1332.     void *hwaccel_context;
    1334.     /**
    1335.      * error
    1336.      * - encoding: Set by libavcodec if flags & AV_CODEC_FLAG_PSNR.
    1337.      * - decoding: unused
    1338.      */
    1339.     uint64_t error[AV_NUM_DATA_POINTERS];
    1341.     /**
    1342.      * DCT algorithm, see FF_DCT_* below
    1343.      * - encoding: Set by user.
    1344.      * - decoding: unused
    1345.      */
    1346.     int dct_algo;
    1347. #define FF_DCT_AUTO    0
    1348. #define FF_DCT_FASTINT 1
    1349. #define FF_DCT_INT     2
    1350. #define FF_DCT_MMX     3
    1351. #define FF_DCT_ALTIVEC 5
    1352. #define FF_DCT_FAAN    6
    1354.     /**
    1355.      * IDCT algorithm, see FF_IDCT_* below.
    1356.      * - encoding: Set by user.
    1357.      * - decoding: Set by user.
    1358.      */
    1359.     int idct_algo;
    1360. #define FF_IDCT_AUTO          0
    1361. #define FF_IDCT_INT           1
    1362. #define FF_IDCT_SIMPLE        2
    1363. #define FF_IDCT_SIMPLEMMX     3
    1364. #define FF_IDCT_ARM           7
    1365. #define FF_IDCT_ALTIVEC       8
    1366. #if FF_API_ARCH_SH4
    1367. #define FF_IDCT_SH4           9
    1368. #endif
    1369. #define FF_IDCT_SIMPLEARM     10
    1370. #if FF_API_UNUSED_MEMBERS
    1371. #define FF_IDCT_IPP           13
    1372. #endif /* FF_API_UNUSED_MEMBERS */
    1373. #define FF_IDCT_XVID          14
    1374. #if FF_API_IDCT_XVIDMMX
    1375. #define FF_IDCT_XVIDMMX       14
    1376. #endif /* FF_API_IDCT_XVIDMMX */
    1377. #define FF_IDCT_SIMPLEARMV5TE 16
    1378. #define FF_IDCT_SIMPLEARMV6   17
    1379. #if FF_API_ARCH_SPARC
    1380. #define FF_IDCT_SIMPLEVIS     18
    1381. #endif
    1382. #define FF_IDCT_FAAN          20
    1383. #define FF_IDCT_SIMPLENEON    22
    1384. #if FF_API_ARCH_ALPHA
    1385. #define FF_IDCT_SIMPLEALPHA   23
    1386. #endif
    1387. #define FF_IDCT_SIMPLEAUTO    128
    1389.     /**
    1390.      * bits per sample/pixel from the demuxer (needed for huffyuv).
    1391.      * - encoding: Set by libavcodec.
    1392.      * - decoding: Set by user.
    1393.      */
    1394.      int bits_per_coded_sample;
    1396.     /**
    1397.      * Bits per sample/pixel of internal libavcodec pixel/sample format.
    1398.      * - encoding: set by user.
    1399.      * - decoding: set by libavcodec.
    1400.      */
    1401.     int bits_per_raw_sample;
    1403. #if FF_API_LOWRES
    1404.     /**
    1405.      * low resolution decoding, 1-> 1/2 size, 2->1/4 size
    1406.      * - encoding: unused
    1407.      * - decoding: Set by user.
    1408.      * Code outside libavcodec should access this field using:
    1409.      * av_codec_{get,set}_lowres(avctx)
    1410.      */
    1411.      int lowres;
    1412. #endif
    1414. #if FF_API_CODED_FRAME
    1415.     /**
    1416.      * the picture in the bitstream
    1417.      * - encoding: Set by libavcodec.
    1418.      * - decoding: unused
    1419.      *
    1420.      * @deprecated use the quality factor packet side data instead
    1421.      */
    1422.     attribute_deprecated AVFrame *coded_frame;
    1423. #endif
    1425.     /**
    1426.      * thread count
    1427.      * is used to decide how many independent tasks should be passed to execute()
    1428.      * - encoding: Set by user.
    1429.      * - decoding: Set by user.
    1430.      */
    1431.     int thread_count;
    1433.     /**
    1434.      * Which multithreading methods to use.
    1435.      * Use of FF_THREAD_FRAME will increase decoding delay by one frame per thread,
    1436.      * so clients which cannot provide future frames should not use it.
    1437.      *
    1438.      * - encoding: Set by user, otherwise the default is used.
    1439.      * - decoding: Set by user, otherwise the default is used.
    1440.      */
    1441.     int thread_type;
    1442. #define FF_THREAD_FRAME   1 ///< Decode more than one frame at once
    1443. #define FF_THREAD_SLICE   2 ///< Decode more than one part of a single frame at once
    1445.     /**
    1446.      * Which multithreading methods are in use by the codec.
    1447.      * - encoding: Set by libavcodec.
    1448.      * - decoding: Set by libavcodec.
    1449.      */
    1450.     int active_thread_type;
    1452.     /**
    1453.      * Set by the client if its custom get_buffer() callback can be called
    1454.      * synchronously from another thread, which allows faster multithreaded decoding.
    1455.      * draw_horiz_band() will be called from other threads regardless of this setting.
    1456.      * Ignored if the default get_buffer() is used.
    1457.      * - encoding: Set by user.
    1458.      * - decoding: Set by user.
    1459.      */
    1460.     int thread_safe_callbacks;
    1462.     /**
    1463.      * The codec may call this to execute several independent things.
    1464.      * It will return only after finishing all tasks.
    1465.      * The user may replace this with some multithreaded implementation,
    1466.      * the default implementation will execute the parts serially.
    1467.      * @param count the number of things to execute
    1468.      * - encoding: Set by libavcodec, user can override.
    1469.      * - decoding: Set by libavcodec, user can override.
    1470.      */
    1471.     int (*execute)(struct AVCodecContext *c, int (*func)(struct AVCodecContext *c2, void *arg), void *arg2, int *ret, int count, int size);
    1473.     /**
    1474.      * The codec may call this to execute several independent things.
    1475.      * It will return only after finishing all tasks.
    1476.      * The user may replace this with some multithreaded implementation,
    1477.      * the default implementation will execute the parts serially.
    1478.      * Also see avcodec_thread_init and e.g. the --enable-pthread configure option.
    1479.      * @param c context passed also to func
    1480.      * @param count the number of things to execute
    1481.      * @param arg2 argument passed unchanged to func
    1482.      * @param ret return values of executed functions, must have space for "count" values. May be NULL.
    1483.      * @param func function that will be called count times, with jobnr from 0 to count-1.
    1484.      *             threadnr will be in the range 0 to c->thread_count-1 < MAX_THREADS and so that no
    1485.      *             two instances of func executing at the same time will have the same threadnr.
    1486.      * @return always 0 currently, but code should handle a future improvement where when any call to func
    1487.      *         returns < 0 no further calls to func may be done and < 0 is returned.
    1488.      * - encoding: Set by libavcodec, user can override.
    1489.      * - decoding: Set by libavcodec, user can override.
    1490.      */
    1491.     int (*execute2)(struct AVCodecContext *c, int (*func)(struct AVCodecContext *c2, void *arg, int jobnr, int threadnr), void *arg2, int *ret, int count);
    1493.     /**
    1494.      * noise vs. sse weight for the nsse comparison function
    1495.      * - encoding: Set by user.
    1496.      * - decoding: unused
    1497.      */
    1498.      int nsse_weight;
    1500.     /**
    1501.      * profile
    1502.      * - encoding: Set by user.
    1503.      * - decoding: Set by libavcodec.
    1504.      */
    1505.      int profile;
    1506. #define FF_PROFILE_UNKNOWN -99
    1507. #define FF_PROFILE_RESERVED -100
    1509. #define FF_PROFILE_AAC_MAIN 0
    1510. #define FF_PROFILE_AAC_LOW  1
    1511. #define FF_PROFILE_AAC_SSR  2
    1512. #define FF_PROFILE_AAC_LTP  3
    1513. #define FF_PROFILE_AAC_HE   4
    1514. #define FF_PROFILE_AAC_HE_V2 28
    1515. #define FF_PROFILE_AAC_LD   22
    1516. #define FF_PROFILE_AAC_ELD  38
    1517. #define FF_PROFILE_MPEG2_AAC_LOW 128
    1518. #define FF_PROFILE_MPEG2_AAC_HE  131
    1520. #define FF_PROFILE_DTS         20
    1521. #define FF_PROFILE_DTS_ES      30
    1522. #define FF_PROFILE_DTS_96_24   40
    1523. #define FF_PROFILE_DTS_HD_HRA  50
    1524. #define FF_PROFILE_DTS_HD_MA   60
    1525. #define FF_PROFILE_DTS_EXPRESS 70
    1527. #define FF_PROFILE_MPEG2_422    0
    1528. #define FF_PROFILE_MPEG2_HIGH   1
    1529. #define FF_PROFILE_MPEG2_SS     2
    1530. #define FF_PROFILE_MPEG2_SNR_SCALABLE  3
    1531. #define FF_PROFILE_MPEG2_MAIN   4
    1532. #define FF_PROFILE_MPEG2_SIMPLE 5
    1534. #define FF_PROFILE_H264_CONSTRAINED  (1<<9)  // 8+1; constraint_set1_flag
    1535. #define FF_PROFILE_H264_INTRA        (1<<11) // 8+3; constraint_set3_flag
    1537. #define FF_PROFILE_H264_BASELINE             66
    1538. #define FF_PROFILE_H264_CONSTRAINED_BASELINE (66|FF_PROFILE_H264_CONSTRAINED)
    1539. #define FF_PROFILE_H264_MAIN                 77
    1540. #define FF_PROFILE_H264_EXTENDED             88
    1541. #define FF_PROFILE_H264_HIGH                 100
    1542. #define FF_PROFILE_H264_HIGH_10              110
    1543. #define FF_PROFILE_H264_HIGH_10_INTRA        (110|FF_PROFILE_H264_INTRA)
    1544. #define FF_PROFILE_H264_HIGH_422             122
    1545. #define FF_PROFILE_H264_HIGH_422_INTRA       (122|FF_PROFILE_H264_INTRA)
    1546. #define FF_PROFILE_H264_HIGH_444             144
    1547. #define FF_PROFILE_H264_HIGH_444_PREDICTIVE  244
    1548. #define FF_PROFILE_H264_HIGH_444_INTRA       (244|FF_PROFILE_H264_INTRA)
    1549. #define FF_PROFILE_H264_CAVLC_444            44
    1551. #define FF_PROFILE_VC1_SIMPLE   0
    1552. #define FF_PROFILE_VC1_MAIN     1
    1553. #define FF_PROFILE_VC1_COMPLEX  2
    1554. #define FF_PROFILE_VC1_ADVANCED 3
    1556. #define FF_PROFILE_MPEG4_SIMPLE                     0
    1557. #define FF_PROFILE_MPEG4_SIMPLE_SCALABLE            1
    1558. #define FF_PROFILE_MPEG4_CORE                       2
    1559. #define FF_PROFILE_MPEG4_MAIN                       3
    1560. #define FF_PROFILE_MPEG4_N_BIT                      4
    1561. #define FF_PROFILE_MPEG4_SCALABLE_TEXTURE           5
    1562. #define FF_PROFILE_MPEG4_SIMPLE_FACE_ANIMATION      6
    1563. #define FF_PROFILE_MPEG4_BASIC_ANIMATED_TEXTURE     7
    1564. #define FF_PROFILE_MPEG4_HYBRID                     8
    1565. #define FF_PROFILE_MPEG4_ADVANCED_REAL_TIME         9
    1566. #define FF_PROFILE_MPEG4_CORE_SCALABLE             10
    1567. #define FF_PROFILE_MPEG4_ADVANCED_CODING           11
    1568. #define FF_PROFILE_MPEG4_ADVANCED_CORE             12
    1569. #define FF_PROFILE_MPEG4_ADVANCED_SCALABLE_TEXTURE 13
    1570. #define FF_PROFILE_MPEG4_SIMPLE_STUDIO             14
    1571. #define FF_PROFILE_MPEG4_ADVANCED_SIMPLE           15
    1573. #define FF_PROFILE_JPEG2000_CSTREAM_RESTRICTION_0   1
    1574. #define FF_PROFILE_JPEG2000_CSTREAM_RESTRICTION_1   2
    1575. #define FF_PROFILE_JPEG2000_CSTREAM_NO_RESTRICTION  32768
    1576. #define FF_PROFILE_JPEG2000_DCINEMA_2K              3
    1577. #define FF_PROFILE_JPEG2000_DCINEMA_4K              4
    1579. #define FF_PROFILE_VP9_0                            0
    1580. #define FF_PROFILE_VP9_1                            1
    1581. #define FF_PROFILE_VP9_2                            2
    1582. #define FF_PROFILE_VP9_3                            3
    1584. #define FF_PROFILE_HEVC_MAIN                        1
    1585. #define FF_PROFILE_HEVC_MAIN_10                     2
    1586. #define FF_PROFILE_HEVC_MAIN_STILL_PICTURE          3
    1587. #define FF_PROFILE_HEVC_REXT                        4
    1589.     /**
    1590.      * level
    1591.      * - encoding: Set by user.
    1592.      * - decoding: Set by libavcodec.
    1593.      */
    1594.      int level;
    1595. #define FF_LEVEL_UNKNOWN -99
    1597.     /**
    1598.      * Skip loop filtering for selected frames.
    1599.      * - encoding: unused
    1600.      * - decoding: Set by user.
    1601.      */
    1602.     enum AVDiscard skip_loop_filter;
    1604.     /**
    1605.      * Skip IDCT/dequantization for selected frames.
    1606.      * - encoding: unused
    1607.      * - decoding: Set by user.
    1608.      */
    1609.     enum AVDiscard skip_idct;
    1611.     /**
    1612.      * Skip decoding for selected frames.
    1613.      * - encoding: unused
    1614.      * - decoding: Set by user.
    1615.      */
    1616.     enum AVDiscard skip_frame;
    1618.     /**
    1619.      * Header containing style information for text subtitles.
    1620.      * For SUBTITLE_ASS subtitle type, it should contain the whole ASS
    1621.      * [Script Info] and [V4+ Styles] section, plus the [Events] line and
    1622.      * the Format line following. It shouldn't include any Dialogue line.
    1623.      * - encoding: Set/allocated/freed by user (before avcodec_open2())
    1624.      * - decoding: Set/allocated/freed by libavcodec (by avcodec_open2())
    1625.      */
    1626.     uint8_t *subtitle_header;
    1627.     int subtitle_header_size;
    1629. #if FF_API_ERROR_RATE
    1630.     /**
    1631.      * @deprecated use the 'error_rate' private AVOption of the mpegvideo
    1632.      * encoders
    1633.      */
    1634.     attribute_deprecated
    1635.     int error_rate;
    1636. #endif
    1638. #if FF_API_VBV_DELAY
    1639.     /**
    1640.      * VBV delay coded in the last frame (in periods of a 27 MHz clock).
    1641.      * Used for compliant TS muxing.
    1642.      * - encoding: Set by libavcodec.
    1643.      * - decoding: unused.
    1644.      * @deprecated this value is now exported as a part of
    1645.      * AV_PKT_DATA_CPB_PROPERTIES packet side data
    1646.      */
    1647.     attribute_deprecated
    1648.     uint64_t vbv_delay;
    1649. #endif
    1651. #if FF_API_SIDEDATA_ONLY_PKT
    1652.     /**
    1653.      * Encoding only and set by default. Allow encoders to output packets
    1654.      * that do not contain any encoded data, only side data.
    1655.      *
    1656.      * Some encoders need to output such packets, e.g. to update some stream
    1657.      * parameters at the end of encoding.
    1658.      *
    1659.      * @deprecated this field disables the default behaviour and
    1660.      *             it is kept only for compatibility.
    1661.      */
    1662.     attribute_deprecated
    1663.     int side_data_only_packets;
    1664. #endif
    1666.     /**
    1667.      * Audio only. The number of "priming" samples (padding) inserted by the
    1668.      * encoder at the beginning of the audio. I.e. this number of leading
    1669.      * decoded samples must be discarded by the caller to get the original audio
    1670.      * without leading padding.
    1671.      *
    1672.      * - decoding: unused
    1673.      * - encoding: Set by libavcodec. The timestamps on the output packets are
    1674.      *             adjusted by the encoder so that they always refer to the
    1675.      *             first sample of the data actually contained in the packet,
    1676.      *             including any added padding.  E.g. if the timebase is
    1677.      *             1/samplerate and the timestamp of the first input sample is
    1678.      *             0, the timestamp of the first output packet will be
    1679.      *             -initial_padding.
    1680.      */
    1681.     int initial_padding;
    1683.     /**
    1684.      * - decoding: For codecs that store a framerate value in the compressed
    1685.      *             bitstream, the decoder may export it here. { 0, 1} when
    1686.      *             unknown.
    1687.      * - encoding: May be used to signal the framerate of CFR content to an
    1688.      *             encoder.
    1689.      */
    1690.     AVRational framerate;
    1692.     /**
    1693.      * Nominal unaccelerated pixel format, see AV_PIX_FMT_xxx.
    1694.      * - encoding: unused.
    1695.      * - decoding: Set by libavcodec before calling get_format()
    1696.      */
    1697.     enum AVPixelFormat sw_pix_fmt;
    1699.     /**
    1700.      * Timebase in which pkt_dts/pts and AVPacket.dts/pts are.
    1701.      * Code outside libavcodec should access this field using:
    1702.      * av_codec_{get,set}_pkt_timebase(avctx)
    1703.      * - encoding unused.
    1704.      * - decoding set by user.
    1705.      */
    1706.     AVRational pkt_timebase;
    1708.     /**
    1709.      * AVCodecDescriptor
    1710.      * Code outside libavcodec should access this field using:
    1711.      * av_codec_{get,set}_codec_descriptor(avctx)
    1712.      * - encoding: unused.
    1713.      * - decoding: set by libavcodec.
    1714.      */
    1715.     const AVCodecDescriptor *codec_descriptor;
    1717. #if !FF_API_LOWRES
    1718.     /**
    1719.      * low resolution decoding, 1-> 1/2 size, 2->1/4 size
    1720.      * - encoding: unused
    1721.      * - decoding: Set by user.
    1722.      * Code outside libavcodec should access this field using:
    1723.      * av_codec_{get,set}_lowres(avctx)
    1724.      */
    1725.      int lowres;
    1726. #endif
    1728.     /**
    1729.      * Current statistics for PTS correction.
    1730.      * - decoding: maintained and used by libavcodec, not intended to be used by user apps
    1731.      * - encoding: unused
    1732.      */
    1733.     int64_t pts_correction_num_faulty_pts; /// Number of incorrect PTS values so far
    1734.     int64_t pts_correction_num_faulty_dts; /// Number of incorrect DTS values so far
    1735.     int64_t pts_correction_last_pts;       /// PTS of the last frame
    1736.     int64_t pts_correction_last_dts;       /// DTS of the last frame
    1738.     /**
    1739.      * Character encoding of the input subtitles file.
    1740.      * - decoding: set by user
    1741.      * - encoding: unused
    1742.      */
    1743.     char *sub_charenc;
    1745.     /**
    1746.      * Subtitles character encoding mode. Formats or codecs might be adjusting
    1747.      * this setting (if they are doing the conversion themselves for instance).
    1748.      * - decoding: set by libavcodec
    1749.      * - encoding: unused
    1750.      */
    1751.     int sub_charenc_mode;
    1752. #define FF_SUB_CHARENC_MODE_DO_NOTHING  -1  ///< do nothing (demuxer outputs a stream supposed to be already in UTF-8, or the codec is bitmap for instance)
    1753. #define FF_SUB_CHARENC_MODE_AUTOMATIC    0  ///< libavcodec will select the mode itself
    1754. #define FF_SUB_CHARENC_MODE_PRE_DECODER  1  ///< the AVPacket data needs to be recoded to UTF-8 before being fed to the decoder, requires iconv
    1756.     /**
    1757.      * Skip processing alpha if supported by codec.
    1758.      * Note that if the format uses pre-multiplied alpha (common with VP6,
    1759.      * and recommended due to better video quality/compression)
    1760.      * the image will look as if alpha-blended onto a black background.
    1761.      * However for formats that do not use pre-multiplied alpha
    1762.      * there might be serious artefacts (though e.g. libswscale currently
    1763.      * assumes pre-multiplied alpha anyway).
    1764.      * Code outside libavcodec should access this field using AVOptions
    1765.      *
    1766.      * - decoding: set by user
    1767.      * - encoding: unused
    1768.      */
    1769.     int skip_alpha;
    1771.     /**
    1772.      * Number of samples to skip after a discontinuity
    1773.      * - decoding: unused
    1774.      * - encoding: set by libavcodec
    1775.      */
    1776.     int seek_preroll;
    1778. #if !FF_API_DEBUG_MV
    1779.     /**
    1780.      * debug motion vectors
    1781.      * Code outside libavcodec should access this field using AVOptions
    1782.      * - encoding: Set by user.
    1783.      * - decoding: Set by user.
    1784.      */
    1785.     int debug_mv;
    1786. #define FF_DEBUG_VIS_MV_P_FOR  0x00000001 //visualize forward predicted MVs of P frames
    1787. #define FF_DEBUG_VIS_MV_B_FOR  0x00000002 //visualize forward predicted MVs of B frames
    1788. #define FF_DEBUG_VIS_MV_B_BACK 0x00000004 //visualize backward predicted MVs of B frames
    1789. #endif
    1791.     /**
    1792.      * custom intra quantization matrix
    1793.      * Code outside libavcodec should access this field using av_codec_g/set_chroma_intra_matrix()
    1794.      * - encoding: Set by user, can be NULL.
    1795.      * - decoding: unused.
    1796.      */
    1797.     uint16_t *chroma_intra_matrix;
    1799.     /**
    1800.      * dump format separator.
    1801.      * can be ", " or "\n      " or anything else
    1802.      * Code outside libavcodec should access this field using AVOptions
    1803.      * (NO direct access).
    1804.      * - encoding: Set by user.
    1805.      * - decoding: Set by user.
    1806.      */
    1807.     uint8_t *dump_separator;
    1809.     /**
    1810.      * ',' separated list of allowed decoders.
    1811.      * If NULL then all are allowed
    1812.      * - encoding: unused
    1813.      * - decoding: set by user through AVOPtions (NO direct access)
    1814.      */
    1815.     char *codec_whitelist;
    1817.     /*
    1818.      * Properties of the stream that gets decoded
    1819.      * To be accessed through av_codec_get_properties() (NO direct access)
    1820.      * - encoding: unused
    1821.      * - decoding: set by libavcodec
    1822.      */
    1823.     unsigned properties;
    1824. #define FF_CODEC_PROPERTY_LOSSLESS        0x00000001
    1825. #define FF_CODEC_PROPERTY_CLOSED_CAPTIONS 0x00000002
    1827.     /**
    1828.      * Additional data associated with the entire coded stream.
    1829.      *
    1830.      * - decoding: unused
    1831.      * - encoding: may be set by libavcodec after avcodec_open2().
    1832.      */
    1833.     AVPacketSideData *coded_side_data;
    1834.     int            nb_coded_side_data;
    1836.     /**
    1837.      * Encoding only.
    1838.      *
    1839.      * For hardware encoders configured to use a hwaccel pixel format, this
    1840.      * field should be set by the caller to a reference to the AVHWFramesContext
    1841.      * describing input frames. AVHWFramesContext.format must be equal to
    1842.      * AVCodecContext.pix_fmt.
    1843.      *
    1844.      * This field should be set before avcodec_open2() is called and is
    1845.      * afterwards owned and managed by libavcodec.
    1846.      */
    1847.     AVBufferRef *hw_frames_ctx;
    1849.     /**
    1850.      * Control the form of AVSubtitle.rects[N]->ass
    1851.      * - decoding: set by user
    1852.      * - encoding: unused
    1853.      */
    1854.     int sub_text_format;
    1855. #define FF_SUB_TEXT_FMT_ASS              0
    1856. #if FF_API_ASS_TIMING
    1857. #define FF_SUB_TEXT_FMT_ASS_WITH_TIMINGS 1
    1858. #endif
    1860. } AVCodecContext;
    • int width, height; 视频有关，画面宽高
    • int coded_width, coded_height; 码流宽高，不同于width/height，当解码出来帧在裁剪出来前输出时画面
    • int gop_size; (group of pictures) GOP画面组大小
    • int max_b_frames; B帧最大值
    • int has_b_frames; 解码器的帧重新排序缓冲区的大小，MPEG-2 1个IBP
    • int sample_rate; 音频采样率
    • int channels; 声道数目

    • enum AVSampleFormat sample_fmt; 音频采样格式，枚举类型

      1. enum AVSampleFormat {  
      2.   AV_SAMPLE_FMT_NONE = -1,  
      3.   AV_SAMPLE_FMT_U8,          ///< unsigned 8 bits  
      4.   AV_SAMPLE_FMT_S16,         ///< signed 16 bits  
      5.   AV_SAMPLE_FMT_S32,         ///< signed 32 bits  
      6.   AV_SAMPLE_FMT_FLT,         ///< float  
      7.   AV_SAMPLE_FMT_DBL,         ///< double  
      9.   AV_SAMPLE_FMT_U8P,         ///< unsigned 8 bits, planar  
      10.   AV_SAMPLE_FMT_S16P,        ///< signed 16 bits, planar  
      11.   AV_SAMPLE_FMT_S32P,        ///< signed 32 bits, planar  
      12.   AV_SAMPLE_FMT_FLTP,        ///< float, planar  
      13.   AV_SAMPLE_FMT_DBLP,        ///< double, planar  
      15.   AV_SAMPLE_FMT_NB           ///< Number of sample formats. DO NOT USE if linking dynamically  
      16. };

    • int frame_size; 一个音频帧里每个声道采样数目

    • int frame_number; 帧数目，解码时是解码器总解码的帧数目，编码时是编码过的帧数目
    • int (get_buffer2)(struct AVCodecContext s, AVFrame *frame, int flags);这个回调被调用，当从buffer中得到每帧的数据时，每个buffer必须使用AVBuffer API进行引用技数

    如下属性将被设置在callback回调之前

    • format
    • width, height(视频)
    • sample_rate, channel_layout, nb_samples(音频)

    如约智惠.png