[Live-devel] presentationTime and B-Frames

[Ross Finlayson]

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>	micalg=sha1; boundary="------------ms050109060700050902090703"
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>Hi!
>
>I'm transcoding MPEG-2 (with B-Frames) into MPEG-4 (without 
>B-Frames, just I and P). Currently I'm just transcoding video, but 
>later the transcoded streams should by able to be synchronised with 
>the source's audio stream:
>
>
>     --------> Audio --------------------------------
>    |                                                |
>------------                                     ------
>|   Source   |                                   | Sink |
>------------                                     ------
>    |                             ------------       |
>     --------> Video ---------> | Transcoder | ------
>                                  ------------
>
>The problem is setting the timestamps correct. Right now I generate 
>them when a frame enters the encoder. But then I lose the 
>information of the incoming frame and won't be able to sync to audio 
>later on, right?
>
>When I just pass the times through by setting fPresentationTime = 
>presentationTime, the transcoded streams "flickers" as if the frames 
>are presented in the wrong order.
>
>Is there a possibility to set the presentation times in a way 
>without losing the ability to sync to the corresponding audio stream?

Note that In your original MPEG-2 stream, with B-frames, the frames 
will be in decoding order, which is different from the display order, 
and thus different from the order of frames in the resulting MPEG-4 
stream (because that doesn't have B frames).  In particular, the 
presentation times in the original MPEG-2 stream, with B-frames, will 
*not* be monotonically increasing.  You will need to reorder the 
presentation times accordingly when you convert the stream to MPEG-4 
(without B-frames).
-- 

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