[FFmpeg-devel] How to specify VFR input with various codecs

Alexandre Ferrieux alexandre.ferrieux
Fri Jul 17 11:37:40 CEST 2009


(I first sent this to ffmpeg-user but got zero reaction.)

I'm live-transcoding input from cameras to MPEG2 TS. When the input 
frame rate can be controlled and fixed, it works like a charm. However, 
in some situations, like sender CPU overload, the effective frame rate 
is variable and falls well below the nominal rate, and the mismatch is 
observable in the viewed MPEG2 stream with periodic stalls. Analysis of 
the PCR says it is incrementing slower than real time, which is 
compatible with a discrepancy between incoming dts and actual 

Q: What is the recommended way of addressing this:

  (a) by using an input container with timestamps (like RTP), with a 
timestamp increment reflecting the slowing down of the emitter ?

  (b) by using a special flag meaning "take input dts from real time" ?

  (c) other ?



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