Re: [AVT] Syncronization of co-located clients?

[<skillzero at gmail.com>]

On 7/2/05, Greg Herlein <gherlein at herlein.com> wrote:
> I've got a scenario where I need to multicast RTP streams to
> multiple clients, and some of those may be within visual (and
> worse, audible) range of another client.
> 
> Is there a profile or other trick to help ensure syncronization
> *between* the clients?  In other words, ensure that the
> presentation of the material from one client is in sync with the
> others nearby?

I may be oversimplifying your problem, but have you looked into using
the NTP and RTP timestamp information in RTCP sender/receiver reports
to synchronize? These RTCP reports allow you to determine the relative
offset of each client to the reference clock of the sender. Using
this, each client can adjust its playout delay to play at an absolute
time that is the same as the other clients.

I'm certainly not an expert, but this is what I am doing to play an
RTP audio stream in sync to multiple clients within audible range of
each other. What I found helpful is the book "RTP: Audio and Video for
the Internet" by Colin Perkins (ISBN 0-672-32248-8). The chapter on
Lip Synchronization describes the process of syncing streams using
RTCP reports.

It would be great to hear about other techniques, experiences, and
reading material.

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