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• Can't get the right formula to set frame pts for a stream using libav

  4 avril 2022, par user1365836

  I'm trying to save a stream of frames as mp4.
Source framerate is not fixed and it stay in the range [15,30]

  


  Encoder params :

  


  ...
eCodec.time_base = AVRational(1,3000);
eCodec.framerate = AVRational(30, 1);
...


  


  Stream params :

  


  eStream = avformat_new_stream(eFormat, null);                
eStream.codecpar = codecParams;
eStream.time_base = eCodec.time_base;


  


  Decoder time_base is 0/1 and it marks each frame with a pts like :

  


  480000
528000
576000
...


  


  PTS(f) is always == PTS(f-1)+48000

  


  Encoding (dFrame is the received frame, micro the elapsed time in microseconds) :

  


  av_frame_copy(eFrame, dFrame);
eFrame.pts = micro*3/1000;


  


  This make the video playing too fast.
I can't understand why, but changing micro*3/1000 to micro*3*4/1000 make the video play at the correct speed (checked against a clock after many minutes of varying fps)

  


  What am I missing ?

  


• ffmpeg : add option -isync

  13 juin 2022, par Gyan Doshi

  ffmpeg : add option -isync
  This is a per-file input option that adjusts an input's timestamps
  
  with reference to another input, so that emitted packet timestamps
  
  account for the difference between the start times of the two inputs.
  Typical use case is to sync two or more live inputs such as from capture
  
  devices. Both the target and reference input source timestamps should be
  
  based on the same clock source.
  If either input lacks starting timestamps, then no sync adjustment is made.
  

  • [DH] doc/ffmpeg.texi
  • [DH] fftools/ffmpeg.h
  • [DH] fftools/ffmpeg_opt.c

• Prevent ffmpeg from collapsing multivalue metadata when converting formats

  30 août 2022, par brjaga

  When using ffmpeg to convert FLAC files to Opus, I'm finding that multivalue metadata fields are getting collapsed into single values.

  


  Here's the command I used :

  


  ffmpeg -i steely_dan-fm.flac steely_dan-fm.opus


  


  And here is one of the resulting tags when viewed with the mutagen library in Python :

  


  >>> flac_metadata['performer']
['Walter Becker (electric guitar, bass)', 'Jeff Porcaro (drums, percussion)', 'Donald Fagen (vocals, piano)', 'Victor Feldman (percussion)', 'Glenn Frey (backing vocals)', 'Don Henley (backing vocals)', 'Tim Schmit (backing vocals)']
>>> opus_metadata['performer']
['Walter Becker (electric guitar, bass);Jeff Porcaro (drums, percussion);Donald Fagen (piano);Victor Feldman (percussion);Donald Fagen (vocals);Glenn Frey (backing vocals);Don Henley (backing vocals);Tim Schmit (backing vocals)']


  


  Note that the former is a list of 9 strings, whereas the latter is a list of only one string.

  


  Relevant section of the Vorbis Comment specification :

  


  


  Field names are not required to be unique (occur once) within a comment header. As an example, assume a track was recorded by three well know [sic] artists ; the following is permissible, and encouraged :

  


  


            ARTIST=Dizzy Gillespie 
          ARTIST=Sonny Rollins 
          ARTIST=Sonny Stitt