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• jpeg2000 : Calculate code-block coord in ff_jpeg2000_init_component()

  1er juillet 2013, par Michael Niedermayer

  jpeg2000 : Calculate code-block coord in ff_jpeg2000_init_component()
  Signed-off-by : Luca Barbato <lu_zero@gentoo.org>
  
  Signed-off-by : Nicolas Bertrand <nicoinattendu@gmail.com>
  
  Signed-off-by : Luca Barbato <lu_zero@gentoo.org>
  

  • [DBH] libavcodec/jpeg2000.c
  • [DBH] libavcodec/jpeg2000dec.c

• ffmpeg : Infinite amount of filters/crossfading dynamic playlist

  30 juillet 2019, par MaPePeR

  I want to use ffmpeg to play a dynamic playlist infinitely. The idea is, that an external command/script is executed to request the path to the next file (using the predicted start-time of the file as an argument) and continue playing files infinitely.

  From the answer to "Using FFMPEG to stream continuously videos files to a RTMP server" i learned, that i need to write a custom demuxer, that is similar to the concat demuxer. The problem arises from the fact, that i want to crossfade between the audio files and from my understanding of the demuxer i would have to implement that functionality into the demuxer itself to be able to do it, because a demuxer can only produce one (or a finite number) audio output stream and you need two to use the acrossfade-filter.

  So i would have to set up the filter graph like this :

  file1 --------------------------------*-->| cross | ---->more filters ---> Output
  
  file2 -----------------*-->| cross |----->| fade  |
  
  file3 --*-->| cross |----->| fade  |
  
        ... ->| fade  |

  Using an infinite number of crossfade-filters.

  Also i would really like to pre-filter(*, e.g. silenceremove) the audio files before cross-fading, which makes it even more complicated and the "implement everything in the demuxer"-approach even worse.

  My current solution would be to implement a custom demuxer that alternates between two output streams and does the prefiltering internally as well as an input-alternating crossfade filter like this :

  files -> | alternating |----->| alternating | ----> more filters--->
  
           |   demuxer*  |----->|  crossfade  |

  The problem i see with this approach is that i would need to send multiple EOF-terminated files from the demuxer to the crossfade-filter and i don’t know if that is even possible/allowed when using the standard ffmpeg functions like ff_request_frame.

  Can you tell me if this approach is feasible or do you have a better solution to this problem or any idea that would make this easier ?

• ffmpeg to calculate audio/visual difference between compressed and non-compressed video

  14 juin 2019, par Asymetr

  I’m trying to calculate the audio + visual difference between a harshly compressed video file and one that hasn’t been.
  I’m using pipes because ultimately I wish this to take src from a camera stream.

  I’ve managed to get the video results that I’m looking for, but I’m struggling with the audio.
  I’ve added a line to invert the phase of the compressed audio, so that when they add up in the blend they should almost cancel each other out, but that doesn’t happen.

  ffmpeg -i input.avi -f avi -c:v libxvid -qscale:v 30 -c:a wmav1 - | \
  
  ffmpeg -i - -f avi -af "aeval='-val(0)':c=same" - | \
  
  ffmpeg -i input.avi -i - -filter_complex "blend=all_mode=difference" -c:v libx264 -crf 18 -f avi - | \
  
  ffplay -

  I can still hear all the audio, when what I should be hearing are solely compression artifacts. thx