[FFmpeg-devel] [PATCH] rtsp: Handling of dynamic rate aka Instant-On aka overbuffering

Michael Niedermayer michaelni
Sun Jan 2 19:19:09 CET 2011

On Sun, Jan 02, 2011 at 03:49:42PM +0200, Martin Storsj? wrote:
> Hi,
> DSS has the feature "dynamic rate" aka Instant-On aka overbuffering, for 
> feeding packets faster than realtime, for starting playback faster.
> This is enabled automatically without explicitly requesting, if using 
> something named "Reliable RTP", or if using TCP interleaving.
> The issue with it being enabled automatically is that it screws with 
> timestamps based on RTCP NTP (which is the only official way of syncing 
> streams afaik). When serving packets faster than realtime, DSS still sends 
> RTCP packets with the current realtime NTP timestamp, but with the current 
> RTP stream timestamp.
> In practice, this leads to emitted timestamps jumping backwards at each 
> RTCP packet. To test it, try this and watch the time counter:
> ffplay rtsp://albin.abo.fi:8554/sample_100kbit.mp4?tcp
> First the timestamps go from 0 to about 14, then jumps back to about 7. 
> This, since the second RTCP packet is sent 7 seconds in the stream, after 
> the server has sent about 14 seconds worth of RTP data.
> I'm not sure how to best fix the RTP timestamping code to cope with this - 
> I'm not sure how to use RTCP at all in this setup, and without RTCP, 
> there's no proper way of syncing the streams together.

how does the official code handle syncing with this?

> The attached patchset requests the server to disable it, since we're not 
> really ready to cope with it currently.

this isnt a very nice solution

Michael     GnuPG fingerprint: 9FF2128B147EF6730BADF133611EC787040B0FAB

I have never wished to cater to the crowd; for what I know they do not
approve, and what they approve I do not know. -- Epicurus
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