[vlc-devel] Re: VLC RTSP client support for Transport Stream 'trick play' operations

Derk-Jan Hartman hartman at videolan.org
Tue Jan 16 15:45:36 CET 2007

On 12-jan-2007, at 21:14, Ross Finlayson wrote:
> FYI, the LIVE555 RTSP server implementation now supports trick play  
> operations (seeking, fast forward, reverse play) on MPEG Transport  
> Stream files.  Note, for example, our new 'media server'  
> application: http://www.live555.com/mediaServer/
> However, VLC - when playing these streams as a RTSP client -  
> currently does not perform these trick play operations correctly  
> from its GUI.  Note that the LIVE555 RTSP client library fully  
> supports trick play operations (note the optional "start", "end"  
> and "scale" parameters to "RTSPClient::playMediaSession()"); it's  
> just that VLC does not pass these parameters (in particular,  
> "scale") when calling the library.
> Could someone please take a look at this?  I suspect that a fix  
> will be quite straightforward, and will give VLC important new  
> functionality - basically, client support for VOD with trick play.
> It's important to note that - apart from the GUI, and the  
> parameters passed to "RTSPClient::playMediaSession()" in the  
> LIVE555 library - the fact that the server is performing a 'trick  
> play' operation is completely transparent to the VLC client.  I.e.,  
> VLC's rendering code will continue to see what it thinks is a  
> regular Transport Stream - with no discontinuity in PCR timestamps  
> - so you won't need to make any changes there.

can we please not use the term "trickplay" ?? it's too confusing,  
spans too many topics etc.
To decode: We need to support the optional paramaters start,end,scale  
of playMediaSession

start is only in use atm when you do seeking. (DEMUX_SET_POSITION)
Just so i can get a few things clear.

1: if i set start=0, and the sdp specifies a starttime, is this still  
automatically taken into account?
2: scale: this corresponds to normal FFW, RW functionality correct?  
not to faster/slower (this would be speed?)
3: is there a way to know wether or not Scale is a supported option  
by the server ?

VLC currently does FFW/RW by simply doing a seek. I need to put the  
scale func. as a preferred method over the current functionality in  
the core, which would be some simple additions. Glen Gray should  
already have some code to start this of as a matter of fact.


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