[mythtv-users] Tips for fixing prebuffering pause and WriteAudio: buffer underrun

Sun Mar 27 23:45:19 UTC 2005

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 get
many  "prebuffering pause" messages, and an occasional "WriteAudio: buffer
underrun". The video stutters during the prebuffering messages.

I done some googling, and tried a few things, but have not been able to
get around this. I am looking for tips on how to find the source of the
problem.

I have tried vmstat on both the frontend and the backend, and don't see
anything that stands out. No swapping, plenty of memory, at least 20% idle
cpu on both ends.

I have the "Extra audio buffering" checked. I tried the "Aggresive
Soundcard Buffering", but it didn't help, so I turned it back off.

I am using ALSA on the frontend, and other than the stutters, it sounds
fine.

Myth 0.17
The backend is a 400MHz K6-3, 2.6.10 kernel, PVR-500MCE, ivtv 0.3.2p.
The frontend is an Epia M10K, 2.6.10 kernel, X.org 6.8.2 with XvMC enabled
(and appears to be working from the logs).

Output of frontend during live tv:
2005-03-27 17:17:34.691 Using protocol version 14
2005-03-27 17:17:37.867 Opening audio device 'default'.
Using XvMC version: 1.0
XvMC found and using VLD surface
2005-03-27 17:17:37.958 Using XV port 64
Fulfilled via DRI at 5898240
Fulfilled via DRI at 6428192
Fulfilled via DRI at 6958144
Fulfilled via DRI at 7488096
Fulfilled via DRI at 8018048
Fulfilled via DRI at 8548000
Fulfilled via DRI at 9077952
Fulfilled via DRI at 9607904
Fulfilled via DRI at 10137856
2005-03-27 17:17:38.629 Using realtime priority.
2005-03-27 17:17:38.647 Changing from None to WatchingLiveTV
2005-03-27 17:17:38.657 Video timing method: DRM
Freed 0 (pool 0)
Freed 10491168 (pool 2)
Fulfilled via DRI at 10491168
2005-03-27 17:17:47.315 prebuffering pause
2005-03-27 17:17:57.877 prebuffering pause
2005-03-27 17:17:58.256 prebuffering pause
2005-03-27 17:17:58.573 prebuffering pause
2005-03-27 17:17:58.889 prebuffering pause
2005-03-27 17:17:59.305 prebuffering pause
2005-03-27 17:17:59.622 prebuffering pause
2005-03-27 17:17:59.938 prebuffering pause
2005-03-27 17:18:00.255 prebuffering pause
2005-03-27 17:18:00.571 prebuffering pause
2005-03-27 17:18:00.887 prebuffering pause
2005-03-27 17:18:00.888 WriteAudio: buffer underrun

Nothing special in the backend log:

2005-03-27 17:17:33.213 adding: myth as a client (events: 0)
2005-03-27 17:17:33.221 adding: myth as a remote ringbuffer
2005-03-27 17:17:33.236 Changing from None to WatchingLiveTV
2005-03-27 17:21:48.355 Changing from WatchingLiveTV to None

vmstat on backend during live tv (ok, bo 0 may be odd, but I didn't see
that before):
procs -----------memory---------- ---swap-- -----io---- --system--
----cpu----
 r  b   swpd   free   buff  cache   si   so    bi    bo   in    cs us sy
id wa
 1  0      0 556680  15192 128336    0    0     0   604 4490  4210  4 38
58  0
 0  0      0 556104  15192 128860    0    0     0   544 4443  4541  5 33
62  0
 0  0      0 555528  15192 129480    0    0     0   640 4113  4917  3 28
69  0
 0  0      0 554952  15192 130052    0    0     0   620 4106  4838  3 28
69  0
 0  0      0 554312  15192 130700    0    0     0     0 4002  5313  2 26
72  0
 0  0      0 553608  15192 131460    0    0     0   668 3937  5112  2 26
72  0
 0  0      0 552840  15192 132188    0    0     0   828 4068  4532  4 34
62  0

And vmstat on frontend:
procs -----------memory---------- ---swap-- -----io---- --system--
----cpu----
 r  b   swpd   free   buff  cache   si   so    bi    bo   in    cs us sy
id wa
 1  0      0 164028      0 168144    0    0     0     0 1754  2035 23 21
56  0
 2  0      0 164028      0 168144    0    0     0     0 2406  2590 24 23
54  0
 0  0      0 163900      0 168144    0    0     0     0 2553  1628 40 49
11  0
 0  0      0 163900      0 168144    0    0     0     0 2342  1973 33 45
22  0
 1  0      0 163900      0 168144    0    0     0     0 3748  2761 39 46
14  0
 0  0      0 163900      0 168144    0    0     0     0 4291  3595 32 42
26  0

Any tips for further figuring this out? One thing I read was to turn off
XvMC, but will that work on an cle266 without the deinterlacing (Bob)?

Thanks,

-Michael

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