[pulseaudio-discuss] Underruns when changing sinks on a 'live stream'

[Arun Raghavan]

On Thu, 2011-06-02 at 17:02 -0500, Alejandro Gonzalez wrote:
> On Wed, 2011-06-01 at 12:18 -0500, Alejandro Gonzalez wrote:
> 
> > I'm using the Ubuntu Natty 0.9.22 version, (I mean the debianized
> > package). I found 2 patches from David Henningsson:
> > 
> > Fighting rewinds: Reduce calls to handle_seek 
> > Fighting rewinds: Seek and write data in the same message
> > 
> > I apply them but it doesn't seem to do any improvement, after a couple
> > of switches I start hearing glitches on the playback.
> > 
> > I guess the issue starts when the 'request to rewinds' and the
> > 'limitation' differs by two-digit magnitudes like in:
> > 
> > D: protocol-native.c: Requesting rewind due to rewrite.
> > D: alsa-sink.c: Requested to rewind 130944 bytes.
> > D: alsa-sink.c: Limited to 2336 bytes.
> > D: alsa-sink.c: before: 292
> > D: alsa-sink.c: after: 292
> > D: alsa-sink.c: Rewound 2336 bytes.
> > D: sink.c: Processing rewind...
> > D: sink-input.c: Have to rewind 2336 bytes on render memblockq.
> > D: sink-input.c: Have to rewind 2160 bytes on implementor.
> > 
> > This usually happens just when the new sink starts rendering, the rest
> > of the differences are just of a few bytes, usually < 50 bytes.
> > 
> > That's why I was asking if there is any parameter I can increase
> > (buffer-sizes/latencies) in order to lower this difference.
> 
> Arun, 
> 
> Answering your post on the other email thread:
> 
> "It would be helpful to see if this happens only on
> GStreamer based applications or all of them."
> 
> I'm seeing to different behaviors here:
> 
> 1) using only 'paplay my_file.wav': I couldn't see progressive
> audio-degradation or a progressive increase of Underruns, but after
> several profile switches I hit a state where the audio is only noise.
> Subsequent playbacks are all noisy. Only after setting a again a new
> profile audio was rendered properly, 
> 
> 2) using gstreamer: After 4-5 profile switching audio start to degrade
> with glitches and Underruns messages increase with each profile switch.
> But, if I let the playback finish and I start a new one, audio is fine
> again, without switching profiles again. 
> 
> So, if you can help me with a couple of functions names I can start
> adding some debug traces. I assume that when the stream is rerouted to a
> new sink, part of the old buffer has to be copied to the new sink
> buffer, right? Maybe there is a bug in this procedure, but I'm not sure
> where to start looking at. 

Nice, thanks for trying to pin this down. I'd suggest you start with
figuring out where the rewind is happening in
pulsecore/protocol-native.c (there are a bunch of callers to
handle_seek() which is what spits the message you see in debug logs).

Cheers,
Arun