[Ccrtp-devel] adapative jitter buffer example

[David Sugar]

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This is a section of code I developed over the last two weekends while
rewriting the Bayonne SIP driver code and working on the Troll server.
It essentially attempts to implement an adaptive jitter buffer in the
run method of a Symmetric RTP stack.  Basically, it waits for some
"initial" packet(s) to arrive, absorbs them, and then backs off to an
additional packet timing frame, before processing further input, one
frame at a time, all the while maintaining a wall clock for streaming of
outgoing data.  If there are dropped (or silence suppressed) inbound
packets, and the input queue hence becomes empty again, it simply
resynchronizes to the next arriving packet(s) all over again.

Federico thinks it could be adapted to be more flexible in the way it
handles jitter by offering a settable jitter timing window larger than
one packet frame, or perhaps even to further modify it's behavior based
on rtcp jitter reports.  I may look at that.  Having an example of a
reference implementation for Jitter handling in ccrtp, at least in in
the documentation, if not in an actual example app, I think also would
be very useful.
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void RTPStream::run(void)
{
        size_t r, n;
        size_t size = info.framesize;
        unsigned char buf[size];
        timeout_t timer;
        bool first = true;
        bool jitter;

        setTimer(0);

        for(;;)
        {
                incTimer(info.framing);
                setCancel(cancelDeferred);
                enter();
                if(source)
                {
                        source->getBuffer(buf, size);
                        putBuffer(buf, size);
                        r = dispatchDataPacket();
                }
                leave();
                setCancel(cancelImmediate);

                if(first)
                {
                        while(isPendingData(0))
                        {
                                setCancel(cancelDeferred);
                                r = takeInDataPacket();
                                if(r < 0)
                                        break;

                                jitter = false;
                                first = false;

                                enter();
                                n = getBuffer(buf, r);
                                if(sink)
                                        sink->putBuffer(buf, n);
                                leave();
                                setCancel(cancelImmediate);
                        }
                }
                else if(jitter)
                {
                        if(isPendingData(0))
                        {
                                setCancel(cancelDeferred);
                                r = takeInDataPacket();
                                if(r < 0)
                                        break;

                                enter();
                                n = getBuffer(buf, r);
                                if(sink)
                                        sink->putBuffer(buf, n);
                                leave();
                                setCancel(cancelImmediate);
                        }
                        else
                                first = true;
                }
                else
                        jitter = true;

                timer = getTimer();

                if(timer)
                        Thread::sleep(timer);
        }
}

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