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• Python : Passing complex (ffmpeg) arguments to Popen

  25 juin 2016, par xaccrocheur

  This ffmpeg Popen invocation works :

  command = ['ffmpeg', '-y',
  
             '-i', filename,
  
             '-filter_complex', 'showwavespic',
  
             '-colorkey', 'red',
  
             '-frames:v', '1',
  
             '-s', '800:30',
  
             '-vsync', '2',
  
             '/tmp/waveform.png']
  
  process = sp.Popen( command, stdin=sp.PIPE, stderr=sp.PIPE)
  
  process.wait()

  But I need to use ’compand, showwavespic’ and this comma seems to be blocking the execution. I also need to pass all sorts of strange characters, like columns and, well, all that you can find in a CLI invocation.

  How can I pass complex arguments ?

• Transcode HLS Segments individually using FFMPEG

  27 mai 2013, par rayh

  I am recording a continuous, live stream to a high-bitrate HLS stream. I then want to asynchronously transcode this to different formats/bitrates. I have this working, mostly, except audio artefacts are appearing between each segment (gaps and pops).

  Here is an example ffmpeg command line :

  ffmpeg -threads 1 -nostdin -loglevel verbose \
  
     -nostdin -y -i input.ts -c:a libfdk_aac \
  
     -ac 2 -b:a 64k -y -metadata -vn output.ts

  Inspecting an example sound file shows that there is a gap at the end of the audio :

  

  And the start of the file looks suspiciously attenuated (although this may not be an issue) :

  

  My suspicion is that these artefacts are happening because transcoding are occurring without the context of the stream as a whole.

  Any ideas on how to convince FFMPEG to produce audio that will fit back into a HLS stream ?

  ** UPDATE 1 **

  Here are the start/end of the original segment. As you can see, the start still appears the same, but the end is cleanly ended at 30s. I expect some degree of padding with lossy encoding, but I there is some way that HLS manages to do gapless playback (is this related to iTunes method with custom metadata ?)

  
  

  ** UPDATED 2 **

  So, I converted both the original (128k aac in MPEG2 TS) and the transcoded (64k aac in aac/adts container) to WAV and put the two side-by-side. This is the result :

  
  

  I'm not sure if this is representative of how a client will play it back, but it seems a bit odd that decoding the transcoded one introduces a gap at the start and makes the segment longer. Given they are both lossy encoding, I would have expected padding to be equally present in both (if at all).

  ** UPDATE 3 **

  According to http://en.wikipedia.org/wiki/Gapless_playback - Only a handful of encoders support gapless - for MP3, I've switched to lame in ffmpeg, and the problem, so far, appears to have gone.

  For AAC (see http://en.wikipedia.org/wiki/FAAC), I have tried libfaac (as opposed to libfdk_aac) and it also seems to produce gapless audio. However, the quality of the latter isn't that great and I'd rather use libfdk_aac is possible.

• Evolution #3603 : Ergonomie des onglets de sélection des plugins

  24 novembre 2015, par RastaPopoulos ♥

  Je suis d’accord que dans de nombreux cas, au lieu d’avoir une interface pleines d’options à choisir / cocher / cumuler, il est plus lisible d’avoir 3 ou 4 cas d’utilisation réels dont on sait qu’ils sont utiles, et n’avoir que ça. Évidemment il faut bien réfléchir alors pour être sûr que ne vont pas apparaitre d’autres cas utiles, qui feraient augmenter le nombre d’onglets. Mais là on est dans une interface très précise, qui ne s’occupent que des plugins, c’est à priori pas un truc qui peut augmenter, où des fonctionnalités peuvent apparaitre ou être ajoutées.

  Et au passage, du coup, au niveau ergonomique, ce sont VRAIMENT sémantiquement des onglets (alors que des "filtres" affichés graphiquement sous forme d’onglets, ce n’était pas du tout pertinent au niveau ergo).