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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)

  


• 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.

  


• Still on Piwik 2 ? Update now to Piwik 3, the most efficient and secure Piwik version

  5 avril 2017, par Piwik Core Team — Community

  It has been almost four months since we released Piwik 3. The major new release came with a new UI, performance and security improvements. If you are still on Piwik 2, the security improvements alone should be worth updating your Piwik now to Piwik 3. We cannot recommend this enough.

  Since the Piwik 3.0 release we have released three new versions that fix over 250 issues including more performance and security issues. And new features : the Life Time Revenue, or the Cross Domain linking feature to track visitors across different domains accurately. Also, most plugins from the Piwik Marketplace are now compatible with Piwik 3 so there is no reason to wait anymore.

  The update to Piwik 3 should be smooth, but may take a while depending on the amount of data you have. If you have any problem with the update, feel free to get in touch with us. At Piwik and at InnoCraft, the company of the makers of Piwik, we have successfully updated many Piwik installations.

  

  Wondering what’s changed ?

  • Piwik 3.0.0 Changelog
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