[Live-devel] Playback Speed

[PROMONET Michel]

            Hi Ross,

I am afraid that the computation is a bit more complex in the ISO (see http://www.staroceans.org.s3-website-us-east-1.amazonaws.com/e-book/ISO-14496-10.pdf)
Divisor is not always 2, it could be 1, 2, 3,4 or 6.
For instance, when divisor is 1 live555MediaServer playback a recorded stream twice slower.

Just to give a quick answer about VLC, the last time I tried, it still use an default framerate of 25fps and this could be override using -h264-fps argument.

Regards,

            Michel.

[@@ THALES GROUP INTERNAL @@]

De : live-devel [mailto:live-devel-bounces at ns.live555.com] De la part de Ross Finlayson
Envoyé : vendredi 5 décembre 2014 00:33
À : LIVE555 Streaming Media - development & use
Objet : Re: [Live-devel] Playback Speed

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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