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• avconv audio and video out of sync

  28 juillet 2015, par bram_aerts

  I have a problem synchronizing audio and video using avconv.
  My goal is to process the video stream with opencv and later put the original audio back on the soundless video.
  The processed video stream will be at the same period of time as the original video, but will have a starting offset of a few minutes.

  I tried to simplify the problem with the following code :

  filename="inputvideo.mp4"
  
  avconv -i $filename -an -ss 30 test.mp4
  
  avconv -i test.mp4 -vn -ss 30 -i $filename -async 1 testmerged.mp4

  The second line removing the audio of the original video and shifting it 30 seconds (emulating what the opencv-code will do).
  The last line putting the video and original audio (shifted 30 seconds) back together.

  I assumed if I’d both shift them the same amount of seconds, they would be neatly synchronized, but curiously the video and audio in the resulting movie are out of sync. It is a static delay of about about 3 seconds (audio is behind).
  The same problem appears when making an interim mp3 file and using this as audio track for the resulting movie.

  When searching for a solution I found none that resolve this.
  I tried to overcome this issue by using the -vsync/-async options. But since there is no timestamp information in the video this doesn’t solve the problem.
  Even with the latest static build of ffmpeg the audio and video are still out of sync.

  Is there anything I overlooked or is it just impossible to sync audio and video in ffmpeg ?
  And if so, What would be a decent and simple replacement for the funcionality I’m looking for ?

• FFMPEG udp input stream and input stream play local file

  15 décembre 2017, par liewjls

  Hoping someone can guide me to the right place. I have a application is being the "middle man" receiving a video stream from a source via UDP and passing this video stream to a ffmpeg instance on a server and record a certain period of the video (without audio), on a certain occasion it will need to play the video from recorded video instead of passing the live video stream to the ffmepg instance on the server.

  /ffmpeg -an -f mpegts -i udp://@:7100/?fifo_size=2000&overrun_nonfatal=1 -analyzeduration 150 -f rawvideo -map 0:0 -vcodec rawvideo -pix_fmt bgra - -af volumedetect -vn -sn -dn -map 0:1 -f mpegts -y -flush_packets 0 udp://127.0.0.1:7208?pkt_size=1316

  I managed to record the video without audio frm Extracting the h264 part of a video file (demuxing)

  The difference is i save the recorded file as "mpegts"

  avformat_alloc_output_context2(&ofmt_ctx_a, NULL,  "mpegts", out_filename_a);

  As soon i need to play from this recorded file, i read every 1316 packets from this file and pass it to the ffmpeg via the localhost port.

  The problem is the ffmpeg seems doesn’t like my recorded file and i noticed it has error msg "DTS 18635855 < 24133055 out of order"

  How do i resolve this issue ?

  Thanks.

• lavc : Use av_gettime_relative

  6 mai 2014, par Olivier Langlois

  lavc : Use av_gettime_relative
  Whenever av_gettime() is used to measure relative period of time,
  
  av_gettime_relative() is prefered as it guarantee monotonic time
  
  on supported platforms.
  Signed-off-by : Martin Storsjö <martin@martin.st>
  

  • [DBH] libavcodec/dct-test.c
  • [DBH] libavcodec/fft-test.c