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• PyAV inconsistency when parsing packets from h264 frames

  3 avril 2022, par Shlomi Uziel

  When producing H.264 frames and decoding them using pyAV, packets are parsed from frames only when invoking the parse methods twice.

  


  Consider the following test H.264 input, created using :

  


  ffmpeg -f lavfi -i testsrc=duration=10:size=1280x720:rate=30 -f image2 -vcodec libx264 -bsf h264_mp4toannexb -force_key_frames source -x264-params keyint=1:scenecut=0 "frame-%4d.h264"

  


  Now, using pyAV to parse the first frame :

  


  import av
codec = av.CodecContext.create('h264', 'r')
with open('/path/to/frame-0001.h264', 'rb') as file_handler:
    chunk = file_handler.read()
    packets = codec.parse(chunk) # This line needs to be invoked twice to parse packets


  


  packets remain empty unless the last line is invoked again (packets = codec.parse(chunk))

  


  Also, for different real life examples I cannot characterize, it seems that decoding frames from packets also require several decode invocations :

  


  packet = packets[0]
frames = codec.decode(packet) # This line needs to be invoked 2-3 times to actually receive frames.


  


  Does anyone know anything about this incosistent behavior of pyAV ?

  


  (Using Python 3.8.12 on macOS Monterey 12.3.1, ffmpeg 4.4.1, pyAV 9.0.2)

  


• avplay : Handle pixel aspect ratio properly

  6 juillet 2014, par Martin Storsjö

  avplay : Handle pixel aspect ratio properly
  This was broken (left half-implemented) in 354468fc12.
  CC : libav-stable@libav.org
  
  Signed-off-by : Martin Storsjö <martin@martin.st>
  

  • [DH] avplay.c

• PowerShell script ffmpeg

  30 mars 2017, par Karma Elite

  Being the good Windows systems admin that I am, I’m finally getting around to learning PowerShell. With that being said, I have no idea what I’m doing (surprise, surprise).

  I thought that it would be a good learning experience for me to play around with PowerShell at home, far away from my production environment. Recently, I’ve begun using FFMPEG to convert all of my .mkv files to .mp4 so I could have better playback support to my PlayStation 3 via Plex, and thought that this would be a good learning experience.

  The command I’ve been running is as follows :

  ffmpeg -i OldVideoName.mkv -vcodec copy -acodec ac3 OldVideoName.mp4

  What I want is have a PowerShell script that will run once, scanning a folder and all sub-folders for .mkv files (Get-ChildItem ".*.mkv"), transcode them to .mp4 via the above command, and place them in the same location as the .mkv with the same naming scheme.

  Example of running the script with D :\Videos as the target directory :

  D :\Videos\home_dvr\movies\video1.mkv —> D :\Videos\home_dvr\video1.mp4
  D :\Videos\home_dvr\tv\video2.mkv —> D :\Videos\home_dvr\tv\video2.mp4

  As you can guess, I can’t figure it out for the life of me. Here’s the latest attempt before giving up.

      $oldvid = Get-ChildItem .\*.mkv -Recurse
  
      $newvid = $oldvid.Name.split(‘.’)[0]; ForEach-Object {
  
              .\ffmpeg.exe -i $oldvid -y -vcodec copy -acodec ac3 $newvid".mp4”
  
      }

  Any help would be appreciated !