Vorbis dev - Sep 2002 - vorbis tool ogg123/oggenc running out of sync while streaming.

Or rather - the ogg123 seems to run faster than the oggenc.

Based on the vorbis toots 1.0_1,3

I've got (on freebsd) a small streaming server which essentially takes the
oss/vox audion input; uses the code from oggenc to make a stream and then
a bit of apache 2.0 to dole that stream out over TCP to various clients:

        setup oss /dev/dspW0.0 16 bit stereo 44k1.
        create ogg/vorbis header
        setup tcp
        while(1) {
                read oss from /dev/dsp.
                cut and paste code from oggenc
                        enced this with default settings
                if (accept) {
                        add client
                        do http GET/200 OK
                        send ogg/vorbis header
                }
                for each client {
                        if buffer empty
                                fill buffer with most recent frame.
                        if buffered
                                send as much buffered as we can
                        if error
                                drop client
                }
        }

One of the clients is a Sharp Zaurus running:

        http://ipaq.vmlinuz.org/ogg/

a native ogg123:

        ./ogg123 http://foo/oggie

The apache server streams reliable and steadily at a 4 - 256kbit rate -
and the TCP connection is clean and steady. And it certainly seems that
the machine is encoding at a steady pace and fast enough.

Now the problem I have is that regardless of how large I make the Zaurus
its input buffer; the decoder always seems to run a little fast - and will
generally deplete the input buffer after a minute or so. I.e. it nicely
buffers 200-300k; and the after a minute or so is down to 0 on the input
buffer - and will linger around that point.

Is there any way to prevent this ? Is it normal to expect some PID like
feedback loop to adjust the time/keep the buffer roughly ? Or are there
clever time stamps in the protocol to ensure this - and should I look for
a bug in ogg123 ?

Thanks ?

Dw

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On Sun, 2002-09-08 at 18:23, Dirk-Willem van Gulik
wrote:
> Now the problem I have is that regardless of how large I make the Zaurus
> its input buffer; the decoder always seems to run a little fast - and will
> generally deplete the input buffer after a minute or so. I.e. it nicely
> buffers 200-300k; and the after a minute or so is down to 0 on the input
> buffer - and will linger around that point.
> 
> Is there any way to prevent this ? Is it normal to expect some PID like
> feedback loop to adjust the time/keep the buffer roughly ? Or are there
> clever time stamps in the protocol to ensure this - and should I look for
> a bug in ogg123 ?
I'm not sure if I understand the problem.  As long as oggenc is encoding
at faster than realtime, then you shouldn't have any streaming issues. 
Since ogg123 is multithreaded, the player works like this (simplified):

[Input buffer] --> (Decoder thread) --> [Output buffer] --> (Playback
thread)-->[Audio device]

(Input buffer contains compressed Vorbis data, Output buffer contains
decoded PCM audio)

The decoder thread in this setup will run as fast as it can until one of
two conditions occurs:

1) The input buffer is empty
2) The output buffer is full

Then it will wait until the condition goes away.  #2 is the usual
blocking condition when playing from disk, and #1 is the usual condition
when streaming.

So having an empty input buffer is actually to be expected (unless you
have a really small output buffer).  Are you losing audio?  If not, I
wouldn't worry.


---
Stan Seibert

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