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• Re-streaming RTSP with higher FPS

  4 février 2021, par AndBondStyle

  I have RTSP stream with very low and non-constant FPS (varying between 0.2 ... 0.5). It is generated using -skip_frame flag to reduce network and CPU usage as much as possible :

  


  ffmpeg -skip_frame nointra -i  -vsync 2 -f rtsp 


  


  As a consequence, it takes a very long time (1 ... 3 minutes) to connect to that stream and see first meaningful image. I want this stream to work with generic players without any tweaks, so my decision was to re-stream it with higher FPS (10, to be exact) :

  


  ffmpeg -i  -vf "fps=fps=10,setpts=N/(10*TB)" -f rtsp 


  


  Not entirely sure how that command is working, but it somehow did the trick and reduced connection time to about 5 seconds. However, I suspect that it's outputting frames in bursts, which is not ideal. For example, if original low-fps stream contains 2 frames which are 3 seconds apart, my re-stream command (probably) does the following :

  


  

  • When the first input frame comes, output a bunch of frames as fast as possible

  


  • Don't output anything for an entire 3 seconds

  


  • When the second frame comes, output 3 * 10 = 30 frames as fast as possible

  


  • Sleep again until new input frame shows up...

  


  


  Is there a way to make my re-stream command output frames evenly (with a constant FPS) ? Or maybe there's another way to reduce RTSP connection (buffering ?) time ?

  


• avfilter/f_ebur128 : add all sample rates support

  4 mars 2021, par Paul B Mahol

  avfilter/f_ebur128 : add all sample rates support
  The magic constants come from the unofficial "ITU-R BS.1770-1 filter
  
  specifications"¹ by Raiden (libebur128) which relies on "Parameter
  
  Quantization in Direct-Form Recursive Audio Filters"² by Brian
  
  Neunaber.
  The constants seem to include a quantization bias, for example :
  
   Vb is supposed to be exactly √Vh in a high shelf filter
  
   the Pre-filter Gain should likely be 4dB
  
   Pre Q and RLB Q are respectively very close to √½ and ½
  Those are not adjusted to prevent the values from drifting away from
  
  the official specifications.
  An alternative to this approach would be to requantize on the fly as
  
  proposed by pbelkner³, where the 48kHz code path would use the exact
  
  specifications constants while derivating constants for other
  
  frequencies.
  [1] : https://www.scribd.com/document/49991813/ITU-R-BS-1770-1-filters
  
  [2] : https://www.scribd.com/document/6531763/Direct-Form-Filter-Parameter-Quantization
  
  [3] : https://hydrogenaud.io/index.php?topic=86116.msg740092#msg740092
  

  • [DH] libavfilter/f_ebur128.c

• avformat/mxf : set stream frame rates for ST 422 essence containers

  6 septembre 2022, par Pierre-Anthony Lemieux

  avformat/mxf : set stream frame rates for ST 422 essence containers
  The MXF demuxer does not currently set AVStream::avg_frame_rate and ::r_frame_rate
  
  when J2K essence is wrapped according to SMPTE ST 422.
  Reviewed-by : Tomas Härdin <tjoppen@acc.umu.se>
  
  Signed-off-by : Andreas Rheinhardt <andreas.rheinhardt@outlook.com>
  

  • [DH] libavformat/mxfdec.c