[vlc-devel] [RFC] VLC RTSP trickplay support

jean-paul.saman at planet.nl jean-paul.saman at planet.nl
Sat Feb 21 13:37:03 CET 2009

While working on RTSP Scale (aka trickplay) to improve the user interface behaviour together with j-b the following issue came up:

Currently the Qt4 interface shows a 'reverse' playback button when the demux supports the DEMUX_CAN_CONTROL_PACE feature. At the moment only our live555 demux module does use this. It basically means that the button is shown for every RTSP server even if it doesn't support 'Scale' functionality.

According to RFC 2326 the 'Scale' header is optional and thus potentially not supported by every RTSP server out there. The only way to determine if this feature is supported by the RTSP server is to send him a PLAY request with a Scale header present. If the RTSP server does not support this, then the response will not include the Scale header.

At the moment VLC has no clue if the RTSP server supports "Scale" or not. If it could then it would be possible to distinguish between RTSP servers that do and those that do not support 'Scale'.

I cooked up a patch for live555 to export a method (hasScale()) which tells if the RTSP server supports scale. The patch is to illustrate a possible approach. Maybe Ross can comment on this approach and share his thoughts on how to best handle this issue.


Jean-Paul Saman.
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