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• Revision 3331 : On ajoute un accès à la configuration dans les menus

  25 avril 2010, par kent1 — Log

  On ajoute un accès à la configuration dans les menus

• Why is the last frame not showing in an MP4 generated by libav ?

  31 octobre 2023, par Ben

  Note : I have a working example of the problem here.

  


  I'm using the libav/ffmpeg API to generate an MP4 with the h264 codec. In my specific situation I'm generating the files with a max number of 2 "B" frames. I'm able to generate an Mp4 with the right number of frames so that a single, lone "B" frame is the very last frame being written. When this happens, the encoder sets that frame's packet to be discarded (I've verified this with ffprobe). The net result is that some players (say, when dropping the MP4 into Edge or Chrome) will display only n-1 total frames (ignoring the discarded packet). Other players, such as VLC, will play the full n frames (not ignoring the discarded packet). So, the result is inconsistent.

  


  ffmpeg.exe itself doesn't appear to have this problem. Instead, it will set what would be the lone "B" frame to a "P" frame. This means the file will play the same regardless of what player is used.

  


  The problem is : I don't know how to mimic ffmpeg's behavior using the SDK so the last frame will play regardless of the player. As far as I can tell I'm closing out the file properly by flushing out the encoder buffers. I must be doing something wrong somewhere.

  


  I provided a link to the full source above, but at a high level I'm initializing the codec context and stream like this :

  


  newStream->codecpar->codec_id = AV_CODEC_ID_H264;
newStream->codecpar->codec_type = AVMEDIA_TYPE_VIDEO;
newStream->codecpar->width = Width;
newStream->codecpar->height = Height;
newStream->codecpar->format = AV_PIX_FMT_YUV420P;
newStream->time_base = { 1, 75 };
avcodec_parameters_to_context(codecContext, newStream->codecpar);


codecContext->time_base = { 1, 75 };
codecContext->gop_size = 30;


  


  I then sit in a loop and use OpenCV to generate frames (each frame has its frame number drawn on it) :

  


  auto matrix = cv::Mat(Height, Width, CV_8UC3, cv::Scalar(0, 0, 0));

std::stringstream ss;
ss << f; 

cv::putText(matrix, ss.str().c_str(), textOrg, fontFace, fontScale, cv::Scalar(255, 255, 255), thickness, 8);


  


  I then write out the frame like this (looping if more data is needed) :

  


  if ((ret = avcodec_send_frame(codecContext, frame)) == 0) {

   ret = avcodec_receive_packet(codecContext, &pkt); 

   if (ret == AVERROR(EAGAIN))
   {
       continue; 
   }
   else
   {
       av_interleaved_write_frame(pFormat, &pkt);
   }
   av_packet_unref(&pkt);
}


  


  And finally I flush out the file at the end like this :

  


  if ((ret = avcodec_send_frame(codecContext, NULL)) == 0)
{
  for (;;)
  {
     if ((ret = avcodec_receive_packet(codecContext, &pkt)) == AVERROR_EOF)
     {
       break;
     }
     else
     {
       ret = av_interleaved_write_frame(pFormat, &pkt);
       av_packet_unref(&pkt);
     }
  }

  av_write_trailer(pFormat);
  avio_close(pFormat->pb);
}


  


  Yet when I play in Chrome, the player ends on frame 6758,

  


  

  


  And in VLC, the player ends on frame 6759.

  


  

  


  What am I doing wrong ?

  


• FFMPEG generated h264/aac mp4 video first frame doesn't report a zero mediaTime using requestVideoFrameCallback html api [closed]

  12 mai 2023, par Daniel Robinson

  I have noticed that mp4 files generated using ffmpeg aren’t reporting a mediaTime of 0 via requestVideoFrameCallback for the first frame however files encoded as webm or via another encoder such as mainconcept its 0.

  


  You can see a demo of the issue here https://randomstuffdr.s3.eu-west-1.amazonaws.com/TEST-v3.HTML
As you increment the frames with video 1 you don’t see video progress until the third button press.

  


  With video 2-4, the mediaTime is 0 and a single press of the button increments the video by one frame.

  


  Browser : Chrome 113.0.5672.92 (Windows 10)

  


  FFMPEG Version : 6.0-essentials_build-www.gyan.dev or N-109421-g9adf02247c-20221216

  


  There was an interesting note on this page related to mediaTime implementation in chrome https://web.dev/requestvideoframecallback-rvfc/

  


  


  Of special interest in this list is mediaTime. In Chromium's
implementation, we use the audio clock as the time source that backs
video.currentTime, whereas the mediaTime is directly populated by the
presentationTimestamp of the frame. The mediaTime is what you should
use if you want to exactly identify frames in a reproducible way,
including to identify exactly which frames you missed.

  


  


  The led me to compare the PTS files of the video and audio stream between the ffmpeg and MC files using ffprobe however these are all zero for the first frames. The one interesting note, is that ffmpeg file seems to interleave video and audio packets in ffprobe while the mainconcept file has 8 video frames before audio, I have no idea if this is significant.

  


  What I would like to know is if there is any way I can make ffmpeg generate a file in a similar manner to mainconcept ? So far I have tried ; disabling b-frames, use baseline profile and avoid_negative_ts

  


  Video 1 – (Video : H264 /Audio : AAC / Wrapper : MP4 / Transcoder : FFMPEG)
.\ffmpeg.exe -i '720p50 Flash and Beep.mxf' -map 0:0 -map 0:1 -map_metadata -1 -c:v libx264 -crf 28 -b:v 118k -maxrate 118k -bufsize 236k -vf scale="480 :-1" -preset veryfast -c:a aac "..\low-res\720p50FlashandBeep_V_A.mp4"

  


  Video 2 – (Video : H264 /Audio : No Audio / Wrapper : MP4 / Transcoder : FFMPEG)
.\ffmpeg.exe -i '720p50 Flash and Beep.mxf' -map 0:0 -map 0:1 -map_metadata -1 -c:v libx264 -crf 28 -b:v 118k -maxrate 118k -bufsize 236k -vf scale="480 :-1" -preset veryfast -an "..\low-res\720p50FlashandBeep_V.mp4"

  


  Video 3 – (Video : vp8 /Audio : ogg / Wrapper : webm / Transcoder : FFMPEG)
.\ffmpeg.exe -i '720p50 Flash and Beep.mxf' -map 0:0 -map 0:1 -map_metadata -1 -c:v vp8 -crf 28 -b:v 118k -maxrate 118k -bufsize 236k -vf scale="480 :-1" -preset veryfast "..\low-res\720p50FlashandBeep_V_A.webm"

  


  Video 4 – (Video : H264 /Audio : AAC / Wrapper : MP4 / Transcoder : MainConcept)