[vlc-devel] Re: Trick mode support for MPEG2 TS

Måns Rullgård mru at inprovide.com
Fri Mar 3 21:19:13 CET 2006

Christophe Burgalat <c.burgalat at broadcastavenue.com> writes:

>> On Fri, 2006-03-03 at 02:00 -0800, yj wrote:
>> > Hi,
>> > I would like to know how to implement the Trick mode
>> > support for MPEG2 TS stream.
>> > Actually, I want to get a RTSP server with the above
>> > feature.
>> There have been patches submitted by glen at lincor.com to provide
>> trickplay support with vlc and Kasenna servers. Works well.
>> Kasenna's are not cheap though.

And there is no end to the pains they cause if you buy them.

> Yes but this patch only concerns VLC as a client, I'm right ?
> It seems to be possible to integrate this feature also in VLC as a RTSP 
> server.
> I began to try developping it (in fact, fast forward only) and even if it 
> sometimes work well, I'm not sure to do it the right way... I wonder how 
> Kasenna server implements this feature.

The Kasenna server creates special fast forward and rewind streams by
extracting I frames from the original file and fudging timestamps.
When a client requests a trick mode the server switches to the
corresponding place in the ff or rew stream.  The server also creates
indexes that let it quickly map between timestamp and file offset for
each of the streams.  At least this is all how it is supposed to work.
It is very easily confused, and can get the indexes offset by several
minutes.  And that's when it doesn't lock up in bizarre ways.

Måns Rullgård
mru at inprovide.com

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