Recherche avancée

Sur d’autres sites (9022)

• avcodec/pngenc : write cLLi and mDVc chunks

  4 février 2024, par Leo Izen

  avcodec/pngenc : write cLLi and mDVc chunks
  These chunks contain the Content Light Level Information and the
  
  Mastering Display Color Volume information that FFmpeg already supports
  
  as AVFrameSideData. This patch adds support for the png encoder to save
  
  this metadata as the corresponding chunks in the PNG stream.
  Signed-off-by : Leo Izen <leo.izen@gmail.com>
  

  • [DH] libavcodec/pngenc.c

• 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"

  &#xA;

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

  &#xA;

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

  &#xA;

  pix_fmt=yuva444p12le

  &#xA;

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

  &#xA;

  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 ??

  &#xA;

• Send info from ffmpeg to text file & then parsing into a new file

  26 octobre 2023, par Preston

  I am trying to scan a directory of .mkv files and output the volume information to out.txt and then parse out.txt for volume_max and send it to log.txt using

  &#xA;

  for %i in (*.mkv) do ffmpeg -i "%i" -af "volumedetect" -vn -sn -dn -f 1>> out.txt 2>&1 | findstr max_volume out.txt > log.txt


  &#xA;

  but I keep getting the error(s) :

  &#xA;

  Missing argument for option 'f'.
Error splitting the argument list: Invalid argument


  &#xA;

  when it runs the ffmpeg command.

  &#xA;

  I do get the out.txt file but it's not complete information for each file that's processed. Also, the log.txt file is always 0 bytes, I assume because out.txt doesn't get to the point of generating the max_volume information for each file before erroring.

  &#xA;

  I know it's got to be something simple but I can't see it. Can anyone shed a bit of light on what I might be doing wrong here ? Thanks !

  &#xA;