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• How can I find get the frame number from a gif file using ffmpeg's AVFormatContext struct ?

  17 décembre 2015, par user1400047

  I searched from all the subnode of AVFormatContext, buf just found the fps. no frame numbers or duration info at all. who can help me ?

• lavu/libm : add exp10 support

  22 décembre 2015, par Ganesh Ajjanagadde

  lavu/libm : add exp10 support
  exp10 is a function available in GNU libm. Looks like no other common
  
  libm has it. This adds support for it to FFmpeg.
  There are essentially 2 ways of handling the fallback :
  
  1. Using pow(10, x)
  
  2. Using exp2(M_LOG2_10 * x).
  First one represents a Pareto improvement, with no speed or accuracy
  
  regression anywhere, but speed improvement limited to GNU libm.
  Second one represents a slight accuracy loss (relative error 1e-13)
  
  for non GNU libm. Speedup of > 2x is obtained on non GNU libm platforms,
  
   30% on GNU libm. These are "average case numbers", another benefit is
  
  the lack of triggering of the well-known terrible worst case paths
  
  through pow.
  Based on reviews, second one chosen. Comment added accordingly.
  Reviewed-by : Hendrik Leppkes <h.leppkes@gmail.com>
  
  Reviewed-by : Michael Niedermayer <michael@niedermayer.cc>
  
  Reviewed-by : Ronald S. Bultje <rsbultje@gmail.com>
  
  Signed-off-by : Ganesh Ajjanagadde <gajjanagadde@gmail.com>
  

  • [DH] configure
  • [DH] libavutil/libm.h

• Server side video mixing

  16 mars 2014, par Nicolas Goy

  I have a serie of video files encoded in mpeg2 (I can change this encoding), and I have to produce a movie in flash flv (this is a requirement, I can't change that encoding).

  One destination movie is a compilation of different source video files.

  I have a playlist defining the destination movie. For example :

  Video file        Position        Offset       Length 
  
  little_gnomes     0               0            8.5
  
  fairies           5.23            0.12         12.234
  
  pixies            14              0            9.2

  Video file is the name of the file, position is when the file should be started (in the master timeline), offset is the offset within the video file, and length is the length of the video to play. The numbers are seconds (in double).

  This would result in something like that (final movie timeline) :

                 0--5.23|--8.5|--14|--17.464|--23.2|
  
  little_nomes   **************
  
  fairies               *********************
  
  pixies                           *****************

  Where video overlaps, the last video to be added override the last one, the audio should be mixed.

  The resulting video track would be :

                 0--5.23|--8.5|--14|--17.464|--23.2|
  
  little_nomes   *******
  
  fairies               ***********
  
  pixies                           *****************

  While the resulting audio would be :

                 0--5.23|--8.5|--14|--17.464|--23.2|
  
  little_nomes   11111112222222
  
  fairies               222222211112222222222
  
  pixies                           22222222221111111

  Where 1 or 2 is the number of mixed audio tracks.

  There can be a maximum of 3 audio tracks.

  I need to write a program which takes the playlist as input and produce the flv file. I'm open to any solution (must be free/open source).

  An existing tool that can do that would be the simplest, but I found none. As for making my own solution, I found only ffmpeg, I was able to do basic things with it, but the documentation is terribly lacking.

  It can be any language, it doesn't have to be super fast (if it takes 30 minutes to build a 1h movie it's fine).

  The solution will run on opensolaris based x64 servers. If I have to use linux, this would work too. But windows is out of the question.