[mythtv-users] Playback causes recording stream corruption

Brian Wood beww at beww.org
Thu Mar 30 00:57:12 UTC 2006

On Mar 29, 2006, at 5:28 PM, Ben Rigby wrote:

> 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.

Sorry to ask such an obvious question, but are you sure that DMA is  
enabled for your drive ???

If so, maybe try "hdparm -tT /dev/hd(n)" to make sure the transfer  
rate is what it should be.

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