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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 - Converting TS frame to PNG creating invalid images

  20 juillet 2015, par spelley

  I am attempting to snag a single frame from a TS live stream and generate a PNG image. The command I’ve been using is :

  ffmpeg -y -i "filenamehere" -f image2 -vframes 1 -s 250x250 ./snapshot-250x250.png

  When doing this on my local Windows machine using the FFMPEG executable, it generates the image as expected. When using Ubuntu, after doing an apt-get install ffmpeg and using the same command, I am generating grey squares with sporadic noise even while targeting the same file with the exact same command.

  Here is the (anonymized) output :

  [h264 @ 0xa256a0] no frame!
  
  [h264 @ 0xa256a0] non-existing SPS 0 referenced in buffering period
  
  [h264 @ 0xa256a0] non-existing PPS referenced
  
  [h264 @ 0xa256a0] non-existing SPS 0 referenced in buffering period
  
  [h264 @ 0xa256a0] non-existing PPS 0 referenced
  
  [h264 @ 0xa256a0] decode_slice_header error
  
  [h264 @ 0xa256a0] non-existing PPS 0 referenced
  
  [h264 @ 0xa256a0] decode_slice_header error
  
  [h264 @ 0xa256a0] non-existing PPS 0 referenced
  
  [h264 @ 0xa256a0] decode_slice_header error
  
  [h264 @ 0xa256a0] non-existing PPS 0 referenced
  
  [h264 @ 0xa256a0] decode_slice_header error
  
  [h264 @ 0xa256a0] no frame!
  
  [mpegts @ 0xa1d1e0] max_analyze_duration reached
  
  [NULL @ 0xa28080] start time is not set in estimate_timings_from_pts
  
  
  
  Seems stream 0 codec frame rate differs from container frame rate: 59.94 (60000/1001) -> 1000.00 (1000/1)
  
  Input #0, mpegts, from '<file here="here">':
  
    Duration: 00:00:09.07, start: 35968.174711, bitrate: 697 kb/s
  
    Program 1
  
      Stream #0.0[0x100]: Video: h264 (High), yuv420p, 1280x720 [PAR 1:1 DAR 16:9], 44.52 fps, 1k tbr, 90k tbn, 59.94 tbc
  
      Stream #0.1[0x101]: Audio: aac, 48000 Hz, stereo, s16, 96 kb/s
  
      Stream #0.2[0x102]: Data: [21][0][0][0] / 0x0015
  
  Incompatible pixel format 'yuv420p' for codec 'png', auto-selecting format 'rgb24'
  
  [buffer @ 0xa43480] w:1280 h:720 pixfmt:yuv420p
  
  [avsink @ 0xa28780] auto-inserting filter 'auto-inserted scaler 0' between the filter 'src' and the filter 'out'
  
  [scale @ 0xa26520] w:1280 h:720 fmt:yuv420p -> w:1280 h:720 fmt:rgb24 flags:0x4
  
  Output #0, image2, to './snapshot-250x250.png':
  
    Metadata:
  
      encoder         : Lavf53.21.1
  
      Stream #0.0: Video: png, rgb24, 1280x720 [PAR 1:1 DAR 16:9], q=2-31, 200 kb/s, 90k tbn, 1k tbc
  
  Stream mapping:
  
    Stream #0.0 -> #0.0
  
  Press ctrl-c to stop encoding
  
  frame=    1 fps=  0 q=0.0 Lsize=      -0kB time=0.01 bitrate= -17.6kbits/s dup=31 drop=0
  
  video:8kB audio:0kB global headers:0kB muxing overhead -100.261749%
  
  </file>

  The initial "no frame !" I believe is just it seeking to the first valid keyframe (And thus no cause for concern) however the only difference from my Windows output is the inclusion of this line :

  Incompatible pixel format 'yuv420p' for codec 'png', auto-selecting format 'rgb24'

  Windows has an encoder of Lavc56.46.100 instead of Lavf53.21.1 and the stream mapping line on Windows has more information :

  Stream #0:0 -> #0:0 **(h264 (native) -> png (native))**

  I’ve attempted to manually seek to frames, change the output format from PNG -> GIF, JPEG and just cant seem to find the issue which has no problems on my local Windows machine. Any advice on where to look would be greatly appreciated ! Below is an example of the garbled output.

  

• Skipping Sequential n Frames Every Selected Time or Frames with FFmpeg [closed]

  23 décembre 2020, par ihyyaA

  How can i stream video by skipping Specific number of Sequential frames or time every selected number of frames or time.
I searched a lot and could not find the code I was looking for.

  


  I tried codes like this :

  


  ffmpeg.exe -re -i "link.m3u8"-vf select="not(mod(n\, 200))" -acodec aac -c:v libx264 -preset veryfast -strict experimental -f flv "rtmp://.."


  


  But the output is one frame every specific frames or time, but i want selected number of Sequential frames every selected period of time or frames.

  


  I think this Question is not Duplicate

  


  Thanks.