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• FFMPEG Seeking with concat demuxer causes video & audio to be out of sync

  20 février 2023, par Garuuk

  I have a very simple use case that's driving me bananas.

  


  My problem and question :

  


  I'm using ffmpeg version 5.1.2 on a MacOS and i'm using ffmpeg seeking and concat demuxer to cut many 1 minute videos into 15 seconds chopped up over 12 clips where every clip is just 2 seconds from the same video (kind of like a mini teasers for the video). I would really like to not have to re-encode to make the video processing as fast as possible.

  


  First, I take each 1 minute video and cut it up into 12 clips (I do all this programmatically in python fwiw)

  


  ffmpeg -ss 0 -i input.mp4 -t 2 -c copy -y cut_1.mp4
ffmpeg -ss 4 -i input.mp4 -t 2 -c copy -y cut_2.mp4
ffmpeg -ss 8 -i input.mp4 -t 2 -c copy -y cut_3.mp4
...
...


  


  I then write all the output file names to my concat_manifest.txt

  


  file cut_1.mp4
file cut_2.mp4
...
...


  


  Then I run my concat command :

  


  ffmpeg -f concat -i concat_manifest.txt -c copy -y concat_video.mp4


  


  This works really fast but the audio and video at the stitch point get out of sync and sometimes the video just chokes & lags. It's mostly not a smooth experience.

  


  What I have tried :

  


  

  1. using the concat protocol with intermediate profiles : ffmpeg.org/wiki/Concatenate#demuxer

  


  2. Putting the -ss when I seek after the -i. This makes everything worse

  


  3. Playing around with different -ss values. This has some noticeable affects but it's not obvious why yet.

  


  4. I've also read from the ffmpeg resource regarding seeking and copying :

  


  


  Which leads me to believe that maybe because ffmpeg is using timestamps instead of frames, seeking isn't accurate using -ss when using the concat demuxer

  


  Is there a way to get concat demuxer cutting and concatenating the video where the audio is somewhat in sync with the video ?

  


  Thanks

  


  EDIT : I found an answer and i'll be posting the solution in the coming few days.

  


• FFmpeg, how to skip late input ?

  14 novembre 2017, par user3343357

  I’m running ffmpeg to display incoming stream on a Decklink BlackMagic card with the following command line :

  ffmpeg -y -f ourFmt -probesize 32 -i - -f decklink -preset ultrafast 
  
     -pix_fmt uyvy422 -s 1920x1080 -r 30 -af volume=0.1 -max_delay 10000 
  
       DeckLink Mini Monitor

  Basically I get the video over the internet by UDP and stream it to ffmpeg stdin. Both audio and video streams have pts and dts and are fully in sync, if the connection is good there is no problems.

  However if there are issues with the connection i start getting errors, sometimes the video delay grows significantly, and audio stops working.
  The errors i get are :

  ffmpeg : [decklink @ 0x26cc600] There are not enough buffered video
  frames. Video may misbehave ! ffmpeg : [decklink @ 0x26cc600] There’s no
  buffered audio. Audio will misbehave ! ffmpeg : Last message
  repeated 4 times ffmpeg : [decklink @ 0x26cc600] There are not enough
  buffered video frames. Video may misbehave ! ffmpeg : [decklink @
  0x26cc600] There’s no buffered audio. Audio will misbehave ! ffmpeg :
  Last message repeated 3 times ffmpeg : frame= 5204 fps= 30 q=-0.0
  size=N/A time=00:02:53.76 bitrate=N/A dup=385 drop=5 speed=0.993x
  ffmpeg : [decklink @ 0x26cc600] There’s no buffered audio. Audio will
  misbehave ! ffmpeg : Last message repeated 18 times ffmpeg :
  [decklink @ 0x26cc600] There are not enough buffered video frames.
  Video may misbehave ! ffmpeg : [decklink @ 0x26cc600] There’s no
  buffered audio. Audio will misbehave !

  The problem is when the connection is back to normal, the video keeps misbehaving until I restart the stream. What I want to do is for FFmpeg to skip to the content of the last second and play synchronized video from there, drop all the late data in between, is it possible ?

• avutil/pixdesc : deprecate AV_PIX_FMT_FLAG_PSEUDOPAL

  29 mars 2018, par wm4

  avutil/pixdesc : deprecate AV_PIX_FMT_FLAG_PSEUDOPAL
  PSEUDOPAL pixel formats are not paletted, but carried a palette with the
  
  intention of allowing code to treat unpaletted formats as paletted. The
  
  palette simply mapped the byte values to the resulting RGB values,
  
  making it some sort of LUT for RGB conversion.
  It was used for 1 byte formats only : RGB4_BYTE, BGR4_BYTE, RGB8, BGR8,
  
  GRAY8. The first 4 are awfully obscure, used only by some ancient bitmap
  
  formats. The last one, GRAY8, is more common, but its treatment is
  
  grossly incorrect. It considers full range GRAY8 only, so GRAY8 coming
  
  from typical Y video planes was not mapped to the correct RGB values.
  
  This cannot be fixed, because AVFrame.color_range can be freely changed
  
  at runtime, and there is nothing to ensure the pseudo palette is
  
  updated.
  Also, nothing actually used the PSEUDOPAL palette data, except xwdenc
  
  (trivially changed in the previous commit). All other code had to treat
  
  it as a special case, just to ignore or to propagate palette data.
  In conclusion, this was just a very strange old mechnaism that has no
  
  real justification to exist anymore (although it may have been nice and
  
  useful in the past). Now it's an artifact that makes the API harder to
  
  use : API users who allocate their own pixel data have to be aware that
  
  they need to allocate the palette, or FFmpeg will crash on them in
  
  _some_ situations. On top of this, there was no API to allocate the
  
  pseuo palette outside of av_frame_get_buffer().
  This patch not only deprecates AV_PIX_FMT_FLAG_PSEUDOPAL, but also makes
  
  the pseudo palette optional. Nothing accesses it anymore, though if it's
  
  set, it's propagated. It's still allocated and initialized for
  
  compatibility with API users that rely on this feature. But new API
  
  users do not need to allocate it. This was an explicit goal of this
  
  patch.
  Most changes replace AV_PIX_FMT_FLAG_PSEUDOPAL with FF_PSEUDOPAL. I
  
  first tried #ifdefing all code, but it was a mess. The FF_PSEUDOPAL
  
  macro reduces the mess, and still allows defining FF_API_PSEUDOPAL to 0.
  Passes FATE with FF_API_PSEUDOPAL enabled and disabled. In addition,
  
  FATE passes with FF_API_PSEUDOPAL set to 1, but with allocation
  
  functions manually changed to not allocating a palette.
  

  • [DH] doc/APIchanges
  • [DH] fftools/ffprobe.c
  • [DH] libavcodec/decode.c
  • [DH] libavcodec/ffv1dec.c
  • [DH] libavcodec/rawdec.c
  • [DH] libavcodec/smvjpegdec.c
  • [DH] libavfilter/drawutils.c
  • [DH] libavfilter/framepool.c
  • [DH] libavfilter/vf_crop.c
  • [DH] libavfilter/vf_pixdesctest.c
  • [DH] libavfilter/vf_scale.c
  • [DH] libavfilter/vf_shuffleplanes.c
  • [DH] libavutil/frame.c
  • [DH] libavutil/imgutils.c
  • [DH] libavutil/internal.h
  • [DH] libavutil/pixdesc.c
  • [DH] libavutil/pixdesc.h
  • [DH] libavutil/version.h
  • [DH] libswscale/swscale_internal.h