[mythtv-users] Playback causes recording stream corruption

[Ben Rigby]

On 3/30/06, Tony Lill <ajlill at ajlc.waterloo.on.ca> wrote:
> It could be that your backend just can't keep up with the video
> stream. I get the following messages a lot more since going to 0.19:
>
> Mar 29 05:01:16 freevo kernel: ivtv0: All encoder MPEG stream buffers are full. Dropping data.
> Mar 29 05:01:16 freevo kernel: ivtv0: Cause: the application is not reading fast enough.
>
> The real cause seems to be that while recording, the same thread
> that's reading from the device is also inserting rows in the
> recoredemarkup table. Lately, after a lot of monkeying to make other
> things not run during recording, I've found that I get these errors
> whenever a recording starts. Coincidently, for the first 30 seconds of
> a recording, the inserts are done every 5 seconds and after, every 30.
>

Hi Tony,

I haven't seen either of those messages on my system. And my problems
are consistent across the length of a recording, I haven't noticed
them as more prevalent during the first 30 seconds. But please send
you patch my way, I'll have a look at anything.

It does appear that the backend doesn't seem able to keep up with the
recording, but I'm at a loss as to why. Even recording and playing
back at once I only get to about 20% CPU usage. The hard drive is a
fairly new drive, and whilst I'm not sure how to check, I'd be
suprised if it couldn't keep up with one recording stream being
written, and one playback stream being read. This is digital SDTV on a
fairly powerful system, it shouldn't be pushing any of the boundaries
of performance. Are there buffers involved in writing recordings to
disk and reading for playback? Can I increase them?

As I haven't seen anyone else report this problem, and there must be
heaps of people recording digital SD streams so the problem must be to
do with my hardware or configuration. I'm hoping one of the more
knowledgable myth users might be able to point me in the right
direction with some further troubleshooting, or some possible cures.