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• Using FFmpeg to detect alpha channel in PR4444 file [closed]

  8 décembre 2023, par Justin Myers

  I wanted to comment on a thread that already exists on this topic in general, but I just signed up to SO and have not earned my contribution credits yet ! If anyone has advice on how to better handle that in the future, I am all ears !!

  


  None-the-less, here is that thread :

  


  A good way to detect alpha channel in a video using ffmpeg/ffprobe

  


  I tried both the answers listed in that post to detect the presence of an alpha channel in a PR4444 video file.

  


  For Gyan's answer, I get the following pixel format from any PR4444 file (regardless if encoded with alpha or no alpha), when running part 1 :

  


  yuva444p12le

  


  As you will see in Gyan's notes, even if a FFprobe returns an "a" in the return string (for the call for pixel format), that does not equate to the presence of an alpha channel. Hence their note for the subsequent (part 2) call...

  


  I then plugged that into the part 2 of Gyan's answer, but that produced an empty from FFmpeg, and a message providing valid arguments to pair with grep. It seems as though -oP is not a valid arg for grep ? Because it wasn't listed in the returned list of options. This is the template I used (pulled verbatim from Gyan's posted solution) :

  


  ffprobe -v 0 -show_entries pixel_format=name:flags=alpha -of compact=p=0 | grep "$PIX_FMT|" | grep -oP "(?<=alpha=)\d"

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  Where $PIX_FMT is to be replaced with yuva444p121e (per Gyan's instructions).

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  I then tried Benji's solution for part 2, but that just returns the following :

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  pix_fmt=yuva444p12le

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  Of course, this isn't any more useful than part 1...

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  I suspect Gyan is on the right track as he mentions part 2 should produce a boolean result for the presence of an alpha channel. However, either I am misunderstanding the syntax of his template, or something has changed in FFprobe since. There is so limited information out there for this specific task. Hoping someone with more experience and knowledge can help shed some light for me ??

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• the ffmpeg python library doesn't work on heroku

  24 mars 2020, par Androeed Hack

  There is a python application (3.6.10) on Heroku. The app has functions for playing music in voice chat when using the FfmegAudio module. When calling the command, it returns an error :

  ...
  
  raise CommandInvokeError(exc) from discord.ext.commands.errors ... AttributeError 'NoneType' object has no attribute 'stop'

  My app has a buildpack package https://github.com/jonathanong/heroku-buildpack-ffmpeg-latest.git
  Localy everthing works.

• fluent-ffmpeg filePath to blob

  10 avril 2020, par J D

  The fluent ffmpeg library generates a screenshot of a given image/video, and returns a file path to that screenshot. I'm wondering if it is possible to get the blob/file object of that screenshot from the library directly ? Instead of having to reading it back in and converting to blob.

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