[vlc-devel] RTSP client 'trick play' support. When will it ever work??

Ross Finlayson finlayson at live555.com
Thu Jul 9 07:14:33 CEST 2009

>  It is simple:
>  in VLC we enable trickplay support for rtsp (pause/seek/fast 
>if and only if the play time is known, that is if p_sys->ms->playEndTime()
>returns a non zero values. It's the only pseudo reliable way to detect VOD
>that I know of).
>  Unfortunatly, using live555MediaServer and the live555 library (even
>with the ts index), it is not the case. It is non zero at first (I think
>after the initial setup), but is reset to zero latter.

Ahh...  Here's what's actually happening (with VLC 1.0.0 and the 
"LIVE555 Media Server") in this case:

1/ The RTSP server returns a SDP description (in response to VLC's 
RTSP "DESCRIBE" command), which contains a "a=range:" attribute 
*with* an end time - e.g.

o=- 1247115776948082 1 IN IP4
s=MPEG Transport Stream, streamed by the LIVE555 Media Server
t=0 0
a=tool:LIVE555 Streaming Media v2009.06.02
a=x-qt-text-nam:MPEG Transport Stream, streamed by the LIVE555 Media Server
m=video 0 RTP/AVP 33
c=IN IP4

2/ VLC, in response, is sending a "PLAY" command *without* an end time:

PLAY rtsp:// RTSP/1.0
CSeq: 12
Session: 1
Range: npt=0.000-
User-Agent: VLC media player (LIVE555 Streaming Media v2009.06.02)

3/ The RTSP server then sends back a "PLAY" response without an end time:

RTSP/1.0 200 OK
CSeq: 12
Date: Thu, Jul 09 2009 05:02:56 GMT
Range: npt=0.000-
Session: 1

So, the real problem is that VLC - in step 2 - is sending a "PLAY" 
command without an end time, despite the fact that the SDP 
description (returned in response to "DESCRIBE") had a range end 
time.  "ms->playEndTime()" *should* be non-zero (because "*ms" was 
created using the SDP description).  Could you please check this??

(BTW, I believe that the server's action in step 3 is correct, 
because it's just mirroring what the client asked.  In any case, 
that's not the problem - the problem is the lack of a range end time 
in the client's "PLAY" request.)

Ross Finlayson
Live Networks, Inc.

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