[mythtv-users] Playback problem -- random short pauses

[Lee McLaren]

Thanks for your work Ken.

Watching my system when it pauses, it seems disk related. The HDD light
comes on hard and stays that way for 5sec and then starts to blink off a few
times and then unpauses.

If you patch fixes the problem, the interesting thing to find out would be
how did it get broken.

best of luck

Lee



On Fri, May 6, 2011 at 11:46 PM, Kenneth Emerson
<kenneth.emerson at gmail.com>wrote:

>
>
> On Tue, May 3, 2011 at 12:46 PM, Kenneth Emerson <
> kenneth.emerson at gmail.com> wrote:
>
>>
>>
>> On Tue, May 3, 2011 at 6:28 AM, Steve Curtis <scurtis at fixation.net>wrote:
>>
> On 24 March 2011 15:03, Kenneth Emerson <kenneth.emerson at gmail.com> wrote:
>>>
>>  I have been following several of the threads on this list (and the
>>>> commit list) that have talked about "stuttering" during playback.
>>>
>>>
>>> I get this too.  I notice that it will always stutter in between
>>> programmes such as when the news is about to start - almost without fail.
>>>  This leads me to think that it must be recording related as one programme
>>> ends and new one starts.
>>>
>>
>>>
>> IIRC, there have been numerous complaints about pauses/stuttering while
>> watching recordings when other recordings started/stopped.  This is really
>> starting to look like disk contention where the recording being watched is
>> not buffering enough to get through the (perfect storm?) disruption.  I
>> haven't studied the code that much, but I believe this is what is called the
>> "Ring Buffer"?  I have seen several commits regarding the size of it, and I
>> was asked (by Taylor Ralph) to apply a patch that affected how the size was
>> determined.
>>
>
>> Maybe one of the devs can point me to a place where I can try making this
>> larger or at least putting some debug in to see if this is the problem.
>>
>
>> -- Ken E.
>>
>
> Last night I modified the routine RingBuffer.cpp
> (method: RingBuffer::CalcReadAheadThresh) to always choose the largest read
> block size.  Whether this was a proper change or not it did seem to
> eliminate the pauses I had been seeing.  I watched approximately four hours
> of recordings without any pausing of the video or audio.  I will leave this
> change in for a week to see if it has really solved the symptoms (if not the
> problem). At that point I might open a ticket with the patch.
>
> Here is the diff for anyone else brave enough to give it a try:
>
> diff --git a/mythtv/libs/libmythtv/RingBuffer.cpp
> b/mythtv/libs/libmythtv/RingBu
> index 8b59616..d4613d6 100644
> --- a/mythtv/libs/libmythtv/RingBuffer.cpp
> +++ b/mythtv/libs/libmythtv/RingBuffer.cpp
> @@ -816,7 +816,10 @@ void RingBuffer::CalcReadAheadThresh(void)
>      rbs            = (estbitrate > 5000)  ? KB128 : rbs;
>      rbs            = (estbitrate > 9000)  ? KB256 : rbs;
>      rbs            = (estbitrate > 18000) ? KB512 : rbs;
> -    readblocksize  = max(rbs,readblocksize);
> +    // readblocksize  = max(rbs,readblocksize); Ticket #8706:
> 8706_debug.diff
> +    //  Try to maximize readahead buffer. By KRE 05/04/2011
> +    rbs = KB512;
> +    readblocksize  = rbs;
>
>      // minumum seconds of buffering before allowing read
>      float secs_min = 0.25;
>
> Regards,
>
> Ken E.
>
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