[Live-devel] Playback Speed

[Ross Finlayson]

> I suppose I could intercept the SPS headers and substitute my own, but looking in the spec, I see no field specifying fps.

The SPS (optionally) contains "time_scale" and "num_units_in_tick" fields, from which a frame rate can be inferred:
	frame_rate = time_scale/(2.0*num_units_in_tick)

FWIW, the LIVE555 code uses this information when it streams (i.e., transmits) H.264 video files.  It parses the SPS, trying to find these two fields (and thus the frame rate).  If these fields are not present, then our code assumes a frame rate of 25 fps.  (If you're interested, you can see this in "liveMedia/H264or5VideoStreamFramer.cpp".)

VLC presumably does something similar when it tries to play such a file (if it has filename suffix ".h264").  (But this is not a VLC mailing list, so questions about VLC belong elsewhere.)

Ross Finlayson
Live Networks, Inc.
http://www.live555.com/

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