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• 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

• 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)

  


• How to make multiple ffmpeg commands run in parallel [duplicate]

  9 février, par Kim Mỹ

  I'm using the following ffmpeg command to compress video :

  


  `nice -n 10 ${ffmpegPath} -i "${chunkPath}" -c:v libx264 -preset fast -crf 28 "${compressedPath}"`


  


  However, when I run two instances of ffmpeg of this command to achieve parallelism :

  


  Either in two child processes within a single Node.js application or in two separate Node.js applications running at the same time, it seems only one command is processed, and the other is skipped.

  


  I've noticed that 2 FFmpeg instances are loaded into RAM and both create a starting file for the final compressed video, they finish compression around the same time. However, the total processing time is effectively doubled compared to compressing a single video file alone, which only takes half the time.

  


  I also try to pass the -threads argument but it produces same result.