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• get UTC time of every video frame using ffmepg

  22 septembre 2015, par MathxH Chen

  I just read a RTSP stream from my IP Camera using FFMPEG. I need to display UTC time of every frame and video frame synchronously. The player GUI I created by Qt.

  At very first, I just use libVLC to implement my requirement. Then, I just found out that LibVLC cannot get UTC timestamp of every frame(https://forum.videolan.org/viewtopic.php?f=4&t=128403), So I was out to move from libvlc to ffmepg. I code a Demo read RTSP using ffmpeg library and print the presentation time of every frame . but I find the presentation time is relative , It start from zero up to end. How I can convert the time to UTC ? RTP Packet’s timestamp is relative, It only need RTCP sender report’s absolute timestamp to calculate the UTC. How can I get the UTC time of every frame using FFMPEG ??

  In FFPMEG every frame has own pts in struct AVFrame, the pts just copied from AVPacket, the struct AVStream has time_base this field, UTC time is equal to time_base*pts ?

  my code snippet as follows :

  //SDL End----------------------
  
  while(av_read_frame(pFormatCtx, packet)>=0){
  
  
  
  
  
      if(packet->stream_index==videoindex){
  
          ret = avcodec_decode_video2(pCodecCtx, pFrame, &got_picture, packet);
  
          if(ret < 0){
  
              printf("Decode Error.\n");
  
              return -1;
  
          }
  
  
  
          int64_t utc = packet->pts * av_q2d(pStream->time_base);
  
          printf("UTC is :%I64d\n", utc);

  What’s Wrong ?

• Time issues in ffmpeg script (MP4 to MP3 conversion)

  16 février 2018, par Alex

  I use the code below as script on my Debian PC to create MP3 files from MP4 video files for adding to podcast app on android phone.

  But each time I click pause/forward time position (not indication) is set up in random way after resuming. Please help improve the code below to solve this problem.

  for f in *.mp4; do
  
    ffmpeg -i "$f" -map 0:a -codec:a libmp3lame -b:a 96k "${f%.mp4}.mp3"
  
  done
  
  for f in *.mp3; do
  
    vbrfix -always -makevbr -lameinfo "$f" "${f%.mp3}.mp3"
  
    rm -rf vbrfix.log vbrfix.tmp
  
  done

• Why container and codec has different time base ?

  19 juillet 2019, par theateist

  I used ffmpeg to get video info. The output is

    Duration: 00:05:57.00, start: 0.000000, bitrate: 611 kb/s Stream #0:0(und): Video: h264 (High) (avc1 / 0x31637661), yuv420p, 808x610, 609 kb/s, 25 fps, 25 tbr, 12800 tbn, 50 tbc

  The time base is used to somehow(this is also my another question) calculate when to decode and show the frame, right ? So whose time base is used, container (12800) or codec (50) ?

  The another question is why tbn=12800 and not 90000 ?