[mythtv-users]Tips for fixing prebuffering pause and WriteAudio:
mcarland at bitsgonewild.net
Fri Apr 1 01:26:26 UTC 2005
On Mar 31, 2005, at 8:04 AM, Tj NG wrote:
> >I seem to have all of my install mistakes corrected, except for one.
> >When I play recorded content all is well. But when I play live TV, I
> >many "*prebuffering* *pause*" messages, and an occasional
> "WriteAudio: buffer
> >underrun". The video stutters during the *prebuffering* messages.
> Did u compile with opengl-vsync on? Once that disabled, playback is
> fine on my machine...
Sadly, no. Always looking for the easy fix.
I turned on full logging on the backend and the frontend, but I'll need
to do some homework before I can total sense of it. It does look like
the audio buffer is constantly low, but until I look into what code is
writing what messages, I won't be able to decode what is happening.
Thinking about this, I came up with what would be a cool debugging
tool. It would be slick if there were dummy sources/sinks, that could
be plugged into myth, and could be used to stress test the various
parts of the system. So there would be a module that acted like a
frontend, and tried to stream data from the backend at a rate that was
stepped up until the backend couldn't keep up, and then printed
statistics. Or a simplified backend that was capable of sending a
simple stream (something like gears) at a high rate and logged stats
about the requests from the frontend.
Maybe this functionality exists, dunno. I do know if I was smarter, I
would write it. I don't know if my problem right now is a slow backend,
frontend, or network. I assume it is not the network, I'm using 100Mbps
with a switch, and I tried copying files over NFS from the backend to
the frontends /dev/null (frontend is diskless, nowhere else to write it
that wouldn't interfere with the network), and noted a fairly decent
Still on my list of things to try is use OSS instead of ALSA. Others
have suggested ALSA may be the culprit, and they may be right, but I
have a feeling it isn't. The problem is usually worse when entering
live tv mode, and then smooths out, and then occasionally appears now
and then. To me it seems like a borderline bandwidth issue somewhere. I
think I'll try bumping down my bitrate.
I did order parts from Monarch to build a new backend. I'm hoping to
use these parts to try and troubleshoot this. If they ever ship.
But thanks for the suggestion.
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