Can not add tmcd stream using libavcodec to replicate behavior of ffmpeg -timecode option

Question

I'm trying to replicate option of command line ffmpeg -timecode in my C/C++ code. For some reasons the tcmd stream is not written to the output file. However the av_dump_format shows it in run time

Here is my minimal test

#include <iostream>
extern "C" {
#include <libavcodec/avcodec.h>
#include <libavformat/avformat.h>
#include <libavutil/avutil.h>
#include <libswscale/swscale.h>
#include <libavutil/opt.h>
#include <libavutil/imgutils.h>
#include <libavutil/samplefmt.h>
}
bool checkProResAvailability() {
  const AVCodec* codec = avcodec_find_encoder_by_name("prores_ks");
  if (!codec) {
    std::cerr << "ProRes codec not available. Please install FFmpeg with ProRes support." << std::endl;
    return false;
  }
  return true;
}

int main(){
  av_log_set_level(AV_LOG_INFO);

  const char* outputFileName = "test_tmcd.mov";
  AVFormatContext* formatContext = nullptr;
  AVCodecContext* videoCodecContext = nullptr;

  if (!checkProResAvailability()) {
    return -1;
  }

  std::cout << "Creating test file with tmcd stream: " << outputFileName << std::endl;

  // Allocate the output format context
  if (avformat_alloc_output_context2(&formatContext, nullptr, "mov", outputFileName) < 0) {
    std::cerr << "Failed to allocate output context!" << std::endl;
    return -1;
  }

  if (avio_open(&formatContext->pb, outputFileName, AVIO_FLAG_WRITE) < 0) {
    std::cerr << "Failed to open output file!" << std::endl;
    avformat_free_context(formatContext);
    return -1;
  }

  // Find ProRes encoder
  const AVCodec* videoCodec = avcodec_find_encoder_by_name("prores_ks");
  if (!videoCodec) {
    std::cerr << "Failed to find the ProRes encoder!" << std::endl;
    avio_close(formatContext->pb);
    avformat_free_context(formatContext);
    return -1;
  }

  // Video stream setup
  AVStream* videoStream = avformat_new_stream(formatContext, nullptr);
  if (!videoStream) {
    std::cerr << "Failed to create video stream!" << std::endl;
    avio_close(formatContext->pb);
    avformat_free_context(formatContext);
    return -1;
  }

  videoCodecContext = avcodec_alloc_context3(videoCodec);
  if (!videoCodecContext) {
    std::cerr << "Failed to allocate video codec context!" << std::endl;
    avio_close(formatContext->pb);
    avformat_free_context(formatContext);
    return -1;
  }

  videoCodecContext->width = 1920;
  videoCodecContext->height = 1080;
  videoCodecContext->pix_fmt = AV_PIX_FMT_YUV422P10;
  videoCodecContext->time_base = (AVRational){1, 30}; // Set FPS: 30
  videoCodecContext->bit_rate = 2000000;

  if (avcodec_open2(videoCodecContext, videoCodec, nullptr) < 0) {
    std::cerr << "Failed to open ProRes codec!" << std::endl;
    avcodec_free_context(&videoCodecContext);
    avio_close(formatContext->pb);
    avformat_free_context(formatContext);
    return -1;
  }

  if (avcodec_parameters_from_context(videoStream->codecpar, videoCodecContext) < 0) {
    std::cerr << "Failed to copy codec parameters to video stream!" << std::endl;
    avcodec_free_context(&videoCodecContext);
    avio_close(formatContext->pb);
    avformat_free_context(formatContext);
    return -1;
  }

  videoStream->time_base = videoCodecContext->time_base;

  // Timecode stream setup
  AVStream* timecodeStream = avformat_new_stream(formatContext, nullptr);
  if (!timecodeStream) {
    std::cerr << "Failed to create timecode stream!" << std::endl;
    avcodec_free_context(&videoCodecContext);
    avio_close(formatContext->pb);
    avformat_free_context(formatContext);
    return -1;
  }

  timecodeStream->codecpar->codec_type = AVMEDIA_TYPE_DATA;
  timecodeStream->codecpar->codec_id = AV_CODEC_ID_TIMED_ID3;
  timecodeStream->codecpar->codec_tag = MKTAG('t', 'm', 'c', 'd'); // Timecode tag
  timecodeStream->time_base = (AVRational){1, 30}; // FPS: 30

  if (av_dict_set(&timecodeStream->metadata, "timecode", "00:00:30:00", 0) < 0) {
    std::cerr << "Failed to set timecode metadata!" << std::endl;
    avcodec_free_context(&videoCodecContext);
    avio_close(formatContext->pb);
    avformat_free_context(formatContext);
    return -1;
  }

  // Write container header
  if (avformat_write_header(formatContext, nullptr) < 0) {
    std::cerr << "Failed to write file header!" << std::endl;
    avcodec_free_context(&videoCodecContext);
    avio_close(formatContext->pb);
    avformat_free_context(formatContext);
    return -1;
  }

  // Encode a dummy video frame
  AVFrame* frame = av_frame_alloc();
  if (!frame) {
    std::cerr << "Failed to allocate video frame!" << std::endl;
    avcodec_free_context(&videoCodecContext);
    avio_close(formatContext->pb);
    avformat_free_context(formatContext);
    return -1;
  }

  frame->format = videoCodecContext->pix_fmt;
  frame->width = videoCodecContext->width;
  frame->height = videoCodecContext->height;

  if (av_image_alloc(frame->data, frame->linesize, frame->width, frame->height, videoCodecContext->pix_fmt, 32) < 0) {
    std::cerr << "Failed to allocate frame buffer!" << std::endl;
    av_frame_free(&frame);
    avcodec_free_context(&videoCodecContext);
    avio_close(formatContext->pb);
    avformat_free_context(formatContext);
    return -1;
  }

  // Fill frame with black
  memset(frame->data[0], 0, frame->linesize[0] * frame->height); // Y plane
  memset(frame->data[1], 128, frame->linesize[1] * frame->height / 2); // U plane
  memset(frame->data[2], 128, frame->linesize[2] * frame->height / 2); // V plane

  // Encode the frame
  AVPacket packet;
  av_init_packet(&packet);
  packet.data = nullptr;
  packet.size = 0;

  if (avcodec_send_frame(videoCodecContext, frame) == 0) {
    if (avcodec_receive_packet(videoCodecContext, &packet) == 0) {
      packet.stream_index = videoStream->index;
      av_interleaved_write_frame(formatContext, &packet);
      av_packet_unref(&packet);
    }
  }

  av_frame_free(&frame);

  // Write a dummy packet for the timecode stream
  AVPacket tmcdPacket;
  av_init_packet(&tmcdPacket);
  tmcdPacket.stream_index = timecodeStream->index;
  tmcdPacket.flags |= AV_PKT_FLAG_KEY;
  tmcdPacket.data = nullptr; // Empty packet for timecode
  tmcdPacket.size = 0;
  tmcdPacket.pts = 0; // Set necessary PTS
  tmcdPacket.dts = 0;
  av_interleaved_write_frame(formatContext, &tmcdPacket);

  // Write trailer
  if (av_write_trailer(formatContext) < 0) {
    std::cerr << "Failed to write file trailer!" << std::endl;
  }

  av_dump_format(formatContext, 0, "test.mov", 1);

  // Cleanup
  avcodec_free_context(&videoCodecContext);
  avio_close(formatContext->pb);
  avformat_free_context(formatContext);

  std::cout << "Test file with timecode created successfully: " << outputFileName << std::endl;

  return 0;
}

The code output is:

Creating test file with tmcd stream: test_tmcd.mov
[prores_ks @ 0x11ce05790] Autoselected HQ profile to keep best quality. It can be overridden through -profile option.
[mov @ 0x11ce04f20] Timestamps are unset in a packet for stream 0. This is deprecated and will stop working in the future. Fix your code to set the timestamps properly
[mov @ 0x11ce04f20] Encoder did not produce proper pts, making some up.
Output #0, mov, to 'test.mov':
  Metadata:
    encoder         : Lavf61.7.100
  Stream #0:0: Video: prores (HQ) (apch / 0x68637061), yuv422p10le, 1920x1080, q=2-31, 2000 kb/s, 15360 tbn
  Stream #0:1: Data: timed_id3 (tmcd / 0x64636D74)
      Metadata:
        timecode        : 00:00:30:00
Test file with timecode created successfully: test_tmcd.mov

The ffprobe output is:

$ ffprobe  test_tmcd.mov
ffprobe version 7.1.1 Copyright (c) 2007-2025 the FFmpeg developers
  built with Apple clang version 16.0.0 (clang-1600.0.26.6)
  configuration: --prefix=/opt/homebrew/Cellar/ffmpeg/7.1.1_3 --enable-shared --enable-pthreads --enable-version3 --cc=clang --host-cflags= --host-ldflags='-Wl,-ld_classic' --enable-ffplay --enable-gnutls --enable-gpl --enable-libaom --enable-libaribb24 --enable-libbluray --enable-libdav1d --enable-libharfbuzz --enable-libjxl --enable-libmp3lame --enable-libopus --enable-librav1e --enable-librist --enable-librubberband --enable-libsnappy --enable-libsrt --enable-libssh --enable-libsvtav1 --enable-libtesseract --enable-libtheora --enable-libvidstab --enable-libvmaf --enable-libvorbis --enable-libvpx --enable-libwebp --enable-libx264 --enable-libx265 --enable-libxml2 --enable-libxvid --enable-lzma --enable-libfontconfig --enable-libfreetype --enable-frei0r --enable-libass --enable-libopencore-amrnb --enable-libopencore-amrwb --enable-libopenjpeg --enable-libspeex --enable-libsoxr --enable-libzmq --enable-libzimg --disable-libjack --disable-indev=jack --enable-videotoolbox --enable-audiotoolbox --enable-neon
  libavutil      59. 39.100 / 59. 39.100
  libavcodec     61. 19.101 / 61. 19.101
  libavformat    61.  7.100 / 61.  7.100
  libavdevice    61.  3.100 / 61.  3.100
  libavfilter    10.  4.100 / 10.  4.100
  libswscale      8.  3.100 /  8.  3.100
  libswresample   5.  3.100 /  5.  3.100
  libpostproc    58.  3.100 / 58.  3.100
Input #0, mov,mp4,m4a,3gp,3g2,mj2, from 'test_tmcd.mov':
  Metadata:
    major_brand     : qt  
    minor_version   : 512
    compatible_brands: qt  
    encoder         : Lavf61.7.100
  Duration: N/A, start: 0.000000, bitrate: N/A
  Stream #0:0[0x1]: Video: prores (HQ) (apch / 0x68637061), yuv422p10le, 1920x1080, 15360 tbn (default)
      Metadata:
        handler_name    : VideoHandler
        vendor_id       : FFMP
$

Spent hours with all AI models, no help. Appeal to the human intelligence now

I wouldn't call this code the C++ code. It's a just sequence of calling the C library APIs. The only C++ thing is "std::cout <<" which is absolutely irrelevant to the question being asked. — Sailor Jerry
– Sailor Jerry, Commented Aug 2 at 4:36
Be kind to read the C++ tag wiki: A question should be tagged with c++ only, if: The code is compiled with a C++ compiler. #include, extern "C", ::, nullptr, << make your code non C in many points. — 3CEZVQ
– 3CEZVQ, Commented Aug 2 at 4:46

Gyan · Accepted Answer · 2025-08-02 04:47:48Z

2

No need to create a separate track. Set "timecode" metadata on either the video AVstream or AVFormatContext. The muxer will create a timecode track.

answered Aug 2 at 4:47

Gyan

94.6k11 gold badges197 silver badges226 bronze badges

Sign up to request clarification or add additional context in comments.

7 Comments

Sailor Jerry Aug 2 at 4:58

Doesn't help. I added ``` av_dict_set(&videoStream->metadata, "timecode", "00:00:30:00", 0) ``` Again av_dump_format() shows it, but not the ffprobe

Gyan Aug 2 at 5:40

Check that video stream's avg_frame_rate is set to non-zero, and of course, you set the metadata before avformat_write_header.

Sailor Jerry Aug 2 at 15:13

Done that. Still the same. Here is the code: github.com/sergei/sailvue/blob/mt-render/ffmpeg/tmcd_test.cpp

Gyan Aug 3 at 4:03

There should be no timecode stream attached to the formatcontext.

Sailor Jerry Aug 3 at 15:37

I see. I removed the timestream completely. Still the same behavior, the av_dump_format() shows timecode in runtime, but ffprobe doesn't (I pushed new version of github.com/sergei/sailvue/blob/mt-render/ffmpeg/tmcd_test.cpp to github. Any suggestions on debugging steps?

Gyan Aug 3 at 16:48

I don't see avg_frame_rate being set for the video stream.

Sailor Jerry Aug 3 at 20:13

Indeed, I'm stupid. Now I added it and everything works just fine. Thanks a lot for your patience with me!

Collectives™ on Stack Overflow

Can not add tmcd stream using libavcodec to replicate behavior of ffmpeg -timecode option

1 Answer 1

7 Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

1 Answer 1

7 Comments

Your Answer

Sign up or log in

Post as a guest

Related