• avformat_alloc_output_context2()/avformat_free_context() //输出上下文
  • avformat_new_stream()
  • avcodec_parameters_copy()
  • avformat_write_header() //生成多媒体文件头
  • av_write_frame()/av_interleaved_write_frame() //写数据，av_interleaved_write_frame用的多一些
  • av_write_trailer() //写文件尾，没有的话内部会执行空函数 ```cpp

    include

    include

    include

    include

    include

static void log_packet(const AVFormatContext fmt_ctx, const AVPacket pkt, const char tag) { AVRational time_base = &fmt_ctx->streams[pkt->stream_index]->time_base; printf(“%s: pts:%s pts_time:%s dts:%s dts_time:%s duration:%s duration_time:%s stream_index:%d\n”, tag, av_ts2str(pkt->pts), av_ts2timestr(pkt->pts, time_base), av_ts2str(pkt->dts), av_ts2timestr(pkt->dts, time_base), av_ts2str(pkt->duration), av_ts2timestr(pkt->duration, time_base), pkt->stream_index); }

int main(int argc, char argv[]) { AVOutputFormat ofmt = NULL; AVFormatContext ifmt_ctx = NULL, ofmt_ctx = NULL; AVPacket pkt;

  1. const char *in_filename, *out_filename;
  2. int ret, i;
  3. int stream_index = 0;
  4. int *stream_mapping = NULL;
  5. int stream_mapping_size = 0;
  7. if (argc < 3) {
  8.     printf("usage: %s input output \n"
  9.            "API example program to remux a media file with libavformat and libavcodec.\n"
  10.            "The output format is guessed according to the file extension.\n"
  11.            "\n", argv[0]);
  12.     return 1;
  13. }
  15. in_filename = argv[1];
  16. out_filename = argv[2];
  18. av_register_all();
  20. if ((ret = avformat_open_input(&ifmt_ctx, in_filename, 0, 0)) < 0) {
  21.     fprintf(stderr, "Could not open input file '%s'", in_filename);
  22.     goto end;
  23. }
  25. if ((ret = avformat_find_stream_info(ifmt_ctx, 0)) < 0) {
  26.     fprintf(stderr, "Failed to retrieve input stream information");
  27.     goto end;
  28. }
  30. av_dump_format(ifmt_ctx, 0, in_filename, 0);
  32. /*创建输出上下文*/
  33. avformat_alloc_output_context2(&ofmt_ctx, NULL, NULL, out_filename);
  34. if (!ofmt_ctx) {
  35.     fprintf(stderr, "Could not create output context\n");
  36.     ret = AVERROR_UNKNOWN;
  37.     goto end;
  38. }
  40. stream_mapping_size = ifmt_ctx->nb_streams;
  41. stream_mapping = av_mallocz_array(stream_mapping_size, sizeof(*stream_mapping));
  42. if (!stream_mapping) {
  43.     ret = AVERROR(ENOMEM);
  44.     goto end;
  45. }
  47. ofmt = ofmt_ctx->oformat;
  49. for (i=0; i<ifmt_ctx->nb_streams; i++) {
  50.     AVStream *out_stream;
  51.     AVStream *in_stream = ifmt_ctx->streams[i];
  52.     AVCodecParameters *in_codecpar = in_stream->codecpar;
  54.     if (in_codecpar->codec_type != AVMEDIA_TYPE_AUDIO &&
  55.        in_codecpar->codec_type != AVMEDIA_TYPE_VIDEO &&
  56.        in_codecpar->codec_type != AVMEDIA_TYPE_SUBTITLE) {
  57.         stream_mapping[i] = -1;
  58.         continue;
  59.     }
  61.     stream_mapping[i] = stream_index++;
  63.     out_stream = avformat_new_stream(ofmt_ctx, NULL);
  64.     if (!out_stream) {
  65.         fprintf(stderr, "Failed allocating output stream\n");
  66.         ret = AVERROR_UNKNOWN;
  67.         goto end;
  68.     }
  70.     ret = avcodec_parameters_copy(out_stream->codecpar, in_codecpar);
  71.     if (ret < 0) {
  72.         fprintf(stderr, "Failed to copy codec parameters\n");
  73.         goto end;
  74.     }
  75.     out_stream->codecpar->codec_tag = 0;
  76. }
  77. av_dump_format(ofmt_ctx, 0, out_filename, 1);
  79. if (!(ofmt->flags & AVFMT_NOFILE)) {
  80.     ret = avio_open(&ofmt_ctx->pb, out_filename, AVIO_FLAG_WRITE);
  81.     if (ret < 0) {
  82.         fprintf(stderr, "Could not open output file '%s'", out_filename);
  83.         goto end;
  84.     }
  85. }
  87. ret = avformat_write_header(ofmt_ctx, NULL);
  88. if (ret < 0) {
  89.     fprintf(stderr, "Error occurred when opening output file\n");
  90.     goto end;
  91. }
  93. while (1) {
  94.     AVStream *in_stream, *out_stream;
  96.     ret = av_read_frame(ifmt_ctx, &pkt);
  97.     if (ret < 0) {
  98.         break;
  99.     }
  101.     in_stream = ifmt_ctx->streams[pkt.stream_index];
  102.     if (pkt.stream_index >= stream_mapping_size || 
  103.        stream_mapping[pkt.stream_index] < 0) {
  104.         av_packet_unref(&pkt);
  105.         continue;
  106.     }
  108.     pkt.stream_index = stream_mapping[pkt.stream_index];
  109.     out_stream = ofmt_ctx->streams[pkt.stream_index];
  110.     log_packet(ifmt_ctx, &pkt, "in");
  112.     /*copy packet*/
  113.     pkt.pts = av_rescale_q_rnd(pkt.pts, in_stream->time_base, out_stream->time_base, AV_ROUND_NEAR_INF|AV_ROUND_PASS_MINMAX);
  114.     pkt.dts = av_rescale_q_rnd(pkt.dts, in_stream->time_base, out_stream->time_base, AV_ROUND_NEAR_INF|AV_ROUND_PASS_MINMAX);
  115.     pkt.duration = av_rescale_q(pkt.duration, in_stream->time_base, out_stream->time_base);
  117.     pkt.pos = -1;
  118.     log_packet(ofmt_ctx, &pkt, "out");
  120.     ret = av_interleaved_write_frame(ofmt_ctx, &pkt);
  121.     if (ret < 0) {
  122.         fprintf(stderr, "Error muxing packet\n");
  123.         break;
  124.     }
  125.     av_packet_unref(&pkt);
  126. }
  127. av_write_trailer(ofmt_ctx);

end:
avformat_close_input(&ifmt_ctx);

  1. if (ofmt_ctx && !(ofmt->flags & AVFMT_NOFILE))
  2.     avio_closep(&ofmt_ctx->pb);
  3. avformat_free_context(ofmt_ctx);
  5. av_freep(&stream_mapping);
  7. if (ret < 0 && ret != AVERROR_EOF) {
  8.     fprintf(stderr, "Error occurred:%s \n", av_err2str(ret));
  9.     return 1;
  10. }
  11. return 0;

}

编译： gcc mp4_flv.c -lavformat -lavutil -lavcodec -o mp4_flv ```