[vlc-devel] live555 RTP receive processing bug? Unable to forget lost packet.

[Ross Finlayson]

> I'm using the live555 RTP plugin in VLC. I'm feeding an RTP stream to it (generated by an RTSP session) that is being carried via multiple CDMA data cards... each network path has unknown and changing delay characteristics... packets arrive out of order, and sometimes they are lost.
> 
> I instrumented the RTP code so that it tells me the history of the RTP sequence numbers at the receiver. 
> 
> It appears that whenever a packet is lost, the receive "hangs"... presumably because it's patiently waiting for an arrival that will never happen?

That is incorrect.  If the RTP sequence number indicates that an incoming RTP packet has been skipped, then the LIVE555 RTP reception code will, indeed, wait for the 'skipped' packet to arrive - but not indefinitely.  The length of time that it will wait is specified by the 'packet reordering threshold'.

By default, this threshold is 100 ms; however, VLC's LIVE555 interface code resets this to 200 ms.

Therefore, in VLC, if an incoming packet is lost, then the code will wait no more than 200 ms for it to arrive, before accepting the loss and continuing to handle the following packets.

Note, BTW, that questions about the LIVE555 code - independent of VLC - are best sent to the "live-devel at lists.live555.com" mailing list (see <http://lists.live555.com/mailman/listinfo/live-devel/> to subscribe), so that you don't bother the VLC developers.  Also, because you're using RTSP, I recommend that you use the "openRTSP" (see <http://www.live555.com/openRTSP/>) command-line tool to test your streams.


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

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