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• Matching loudness of commentary track with FFmpeg

  9 mai 2017, par Jon Sangster

  I am using FFmpeg to mix a MP3 file containing a commentary track into the soundtrack of multimedia file. So far I have had great success using FFmpeg’s sidechaincompress filter to auto-duck the soundtrack stream before mixing in the commentary. You can hear the commentary clearly, even when there’s loud music or explosions going on in the film.

  Awesome.

  However, the issue I have now is during the very quiet scenes. When the soundtrack is very quiet, the commentary seems far too loud. If I adjust the volume of the entire commentary track so that it sounds right during the quiet scenes, it’s too heard to hear during the loud scenes.

  My current idea is to somehow use the sidechaincompress filter to duck the commentary track as well, before finally mixing it into the soundtrack. The problem though is that sidechaincompress compresses the target’s volume when the source is loud, but I need the volume to be compressed when the source is quiet.

  I have to admit that I am a quiet the newbie in this domain, so I may coming at this entirely wrong. I’m happy for any advice you can provide !

• ffmpeg - invalid duration

  22 septembre 2016, par OmidAntiLong

  For a project I’m working on I have a small bash script that loops over an input csv file of timecodes, and uses ffmpeg to create screenshots of a given film at each timecode. The csv file is in the format hh:mm:ss,id - it looks like this (extract)

  00:00:08,1
  
  00:00:49,2
  
  00:01:30,3
  
  00:02:38,4
  
  00:03:46,5
  
  00:04:08,6
  
  00:04:26,7
  
  00:04:37,8
  
  00:04:49,9
  
  00:05:29,10
  
  00:05:52,11
  
  00:06:00,12
  
  00:06:44,13
  
  00:07:49,14
  
  00:08:32,15
  
  00:09:28,16
  
  00:10:17,17
  
  00:10:44,18
  
  00:11:48,19
  
  00:12:07,20

  I’ve used it without issue in the past, but today I’ve come to update some of the films and I’m getting a weird issue where ffmpeg is complaining that my input timecode is invalid, despite being in the right format.

  The new input csv files are the same format as the old ones, but it seems like every so often ffmpeg drops the hours from the hh:mm:ss timestamp. If I comment out the ffmpeg line, everything prints to the terminal as expected (but obviously I get no screenshots).

  This is my loop code :

  while read code a
  
  do
  
    echo $code
  
    f="$(printf "%03d" $i)"
  
  
  
    ffmpeg -loglevel error -y -ss $code -i $FILM -vframes 1 -q:v 2 $OUTPUT/$f.jpg
  
  
  
    ((i++))
  
  done < $INPUT

  I’ve tried all sorts, including padding the csv with extra 0s - which works until the hours tick over to 01.

  

  Does anyone have any ideas ? I’m scratching my head.

  Cheers

• Rescaling and slowing down a movie at the same time with ffmpeg

  21 décembre 2016, par ejl62

  I would like with ffmpeg to slow down a movie I am creating using the flag :

  -filter:v "setpts=2.0*PTS"

  However the height of my still images is not divisible by 2, so to avoid the error : height not divisible by 2 (1238x833), I am using the flag :

  -vf scale="trunc(iw/2)*2:trunc(ih/2)*2"

  (I also tried -vf scale=1238:-2).

  When I do this the film is generated but it isn’t slowed down, like if the -filter:v "setpts=2.0*PTS" wasn’t there.

  Is there something particular to do in order to have both option working at the same time ?

  Here is the complete command I am using :

  ffmpeg -an -i ./movie/cphmd1.%05d.ppm -vcodec libx264 -pix_fmt yuv420p -b:v 5000k -r 24 -crf 18 -filter:v "setpts=2.0*PTS" -vf scale="trunc(iw/2)*2:trunc(ih/2)*2" -preset slow -f mp4 cphmd1_slower.mp4

  Many thanks in advance !