Mailing List Archive: MythTV: Mythtvnz

Audio sync issued with DVBS, mythbunut 12.04 and mythtv 0.25

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steven at openmedia

Jun 17, 2012, 12:15 AM

Post #1 of 10 (936 views)
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Audio sync issued with DVBS, mythbunut 12.04 and mythtv 0.25

Hi Guys

Ran an upgrade over the weekend and I noticed that David had the same
issue over on the MythTV Users list.

Basically if I ffwd or jump within a DVB-S recording, in particular a TVNZ
stream, audio sync is lost unless I exit playback and re-open the file.

He's already raised a ticket for the issue
http://code.mythtv.org/trac/ticket/10797

Anyone else here seeing wit with DVB-S material

I'm currently running 2:0.25.0+fixes.20120614

Tried the usual obvious stuff. Any other ideas?

--------------------------------------------
Steven Ellis - Technical Director
OpenMedia Limited - The Home of myPVR
email - steven [at] openmedia
website - http://www.openmedia.co.nz

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steven at openmedia

Jun 18, 2012, 1:53 AM

Post #2 of 10 (873 views)
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Re: Audio sync issued with DVBS, mythbunut 12.04 and mythtv 0.25 [In reply to]

On Sun, June 17, 2012 7:15 pm, Steven Ellis wrote:
> Hi Guys
>
> Ran an upgrade over the weekend and I noticed that David had the same
> issue over on the MythTV Users list.
>
> Basically if I ffwd or jump within a DVB-S recording, in particular a TVNZ
> stream, audio sync is lost unless I exit playback and re-open the file.
>
> He's already raised a ticket for the issue
> http://code.mythtv.org/trac/ticket/10797
>
> Anyone else here seeing wit with DVB-S material
>
> I'm currently running 2:0.25.0+fixes.20120614
>
> Tried the usual obvious stuff. Any other ideas?

Looks like I've got a fix and updated the ticket with the details. Argh
Alsa buffers.

--------------------------------------------
Steven Ellis - Technical Director
OpenMedia Limited - The Home of myPVR
email - steven [at] openmedia
website - http://www.openmedia.co.nz

_______________________________________________
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stephen_agent at jsw

Jun 18, 2012, 2:53 AM

Post #3 of 10 (876 views)
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Re: Audio sync issued with DVBS, mythbunut 12.04 and mythtv 0.25 [In reply to]

On Mon, 18 Jun 2012 20:53:44 +1200 (NZST), you wrote:

>
>On Sun, June 17, 2012 7:15 pm, Steven Ellis wrote:
>> Hi Guys
>>
>> Ran an upgrade over the weekend and I noticed that David had the same
>> issue over on the MythTV Users list.
>>
>> Basically if I ffwd or jump within a DVB-S recording, in particular a TVNZ
>> stream, audio sync is lost unless I exit playback and re-open the file.
>>
>> He's already raised a ticket for the issue
>> http://code.mythtv.org/trac/ticket/10797
>>
>> Anyone else here seeing wit with DVB-S material
>>
>> I'm currently running 2:0.25.0+fixes.20120614
>>
>> Tried the usual obvious stuff. Any other ideas?
>
>Looks like I've got a fix and updated the ticket with the details. Argh
>Alsa buffers.

I thought I remembered something about ALSA buffer problems with 0.24.
A search of my /etc files turned up this in my rc.local:

# Fix for getting these errors in mythfrontend.log:
# ALSA, Error: Setting hardware audio buffer size to 6016
# ALSA, Error: Error opening /proc/asound/card0/pcm0p/sub0/prealloc:
Permission denied.
# ALSA, Error: Try to manually increase audio buffer with: echo 6016
| sudo tee /proc/asound/card0/pcm0p/sub0/prealloc
# ALSA, Error: Unable to sufficiently increase ALSA hardware buffer
size - underruns are likely
# ALSA, Error: WriteAudio: buffer underrun
chmod a+rwx /proc/asound/card0/pcm0p/sub0/prealloc
chgrp audio /proc/asound/card0/pcm0p/sub0/prealloc

With that fix in place, I did a

cat /proc/asound/card0/pcm0p/sub0/prealloc

and got a value of 4096.

What sort of default value does Mythbuntu 12.04 have for this? Would
the same fix help?

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dmoo1790 at ihug

Jun 18, 2012, 3:01 AM

Post #4 of 10 (879 views)
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Re: Audio sync issued with DVBS, mythbunut 12.04 and mythtv 0.25 [In reply to]

On 18/06/12 21:53, Stephen Worthington wrote:
> On Mon, 18 Jun 2012 20:53:44 +1200 (NZST), you wrote:
>
>>
>> On Sun, June 17, 2012 7:15 pm, Steven Ellis wrote:
>>> Hi Guys
>>>
>>> Ran an upgrade over the weekend and I noticed that David had the same
>>> issue over on the MythTV Users list.
>>>
>>> Basically if I ffwd or jump within a DVB-S recording, in particular a TVNZ
>>> stream, audio sync is lost unless I exit playback and re-open the file.
>>>
>>> He's already raised a ticket for the issue
>>> http://code.mythtv.org/trac/ticket/10797
>>>
>>> Anyone else here seeing wit with DVB-S material
>>>
>>> I'm currently running 2:0.25.0+fixes.20120614
>>>
>>> Tried the usual obvious stuff. Any other ideas?
>>
>> Looks like I've got a fix and updated the ticket with the details. Argh
>> Alsa buffers.
>
> I thought I remembered something about ALSA buffer problems with 0.24.
> A search of my /etc files turned up this in my rc.local:
>
> # Fix for getting these errors in mythfrontend.log:
> # ALSA, Error: Setting hardware audio buffer size to 6016
> # ALSA, Error: Error opening /proc/asound/card0/pcm0p/sub0/prealloc:
> Permission denied.
> # ALSA, Error: Try to manually increase audio buffer with: echo 6016
> | sudo tee /proc/asound/card0/pcm0p/sub0/prealloc
> # ALSA, Error: Unable to sufficiently increase ALSA hardware buffer
> size - underruns are likely
> # ALSA, Error: WriteAudio: buffer underrun
> chmod a+rwx /proc/asound/card0/pcm0p/sub0/prealloc
> chgrp audio /proc/asound/card0/pcm0p/sub0/prealloc
>
> With that fix in place, I did a
>
> cat /proc/asound/card0/pcm0p/sub0/prealloc
>
> and got a value of 4096.
>
> What sort of default value does Mythbuntu 12.04 have for this? Would
> the same fix help?
>

Tried that even though I wasn't getting buffer underruns. Still major
unsync when seeking back to recording start and minor unsync when
seeking forward.

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jyavenard at gmail

Jun 18, 2012, 7:01 AM

Post #5 of 10 (877 views)
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Re: Audio sync issued with DVBS, mythbunut 12.04 and mythtv 0.25 [In reply to]

On Monday, 18 June 2012, Stephen Worthington wrote:

>
>
> cat /proc/asound/card0/pcm0p/sub0/prealloc
>
> and got a value of 4096.
>
> What sort of default value does Mythbuntu 12.04 have for this? Would
> the same fix help?
>
>
4096 is the default set by Ubuntu for HDA cards.
It's more than enough...

stephen_agent at jsw

Jun 18, 2012, 8:19 AM

Post #6 of 10 (872 views)
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Re: Audio sync issued with DVBS, mythbunut 12.04 and mythtv 0.25 [In reply to]

On Mon, 18 Jun 2012 07:01:14 -0700, you wrote:

>On Monday, 18 June 2012, Stephen Worthington wrote:
>
>>
>>
>> cat /proc/asound/card0/pcm0p/sub0/prealloc
>>
>> and got a value of 4096.
>>
>> What sort of default value does Mythbuntu 12.04 have for this? Would
>> the same fix help?
>>
>>
>4096 is the default set by Ubuntu for HDA cards.
>It's more than enough...

That explains why I do not remember it being that big before. I have
changed to a new motherboard with HDA audio. IIRC, the old
motherboard was AC-97.

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steven at openmedia

Jun 19, 2012, 1:03 AM

Post #7 of 10 (868 views)
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Re: Audio sync issued with DVBS, mythbunut 12.04 and mythtv 0.25 [In reply to]

On Tue, June 19, 2012 2:01 am, Jean-Yves Avenard wrote:
> On Monday, 18 June 2012, Stephen Worthington wrote:
>
>>
>>
>> cat /proc/asound/card0/pcm0p/sub0/prealloc
>>
>> and got a value of 4096.
>>
>> What sort of default value does Mythbuntu 12.04 have for this? Would
>> the same fix help?
>>
>>
> 4096 is the default set by Ubuntu for HDA cards.
> It's more than enough...

Just upgraded to 12.04 and I'm getting a different value

cat /proc/asound/card0/pcm0p/sub0/prealloc
64

--------------------------------------------
Steven Ellis - Technical Director
OpenMedia Limited - The Home of myPVR
email - steven [at] openmedia
website - http://www.openmedia.co.nz

_______________________________________________
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jyavenard at gmail

Jun 20, 2012, 11:47 PM

Post #8 of 10 (850 views)
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Re: Audio sync issued with DVBS, mythbunut 12.04 and mythtv 0.25 [In reply to]

On 19 June 2012 18:03, Steven Ellis <steven [at] openmedia> wrote:
> Just upgraded to 12.04 and I'm getting a different value
>
> cat /proc/asound/card0/pcm0p/sub0/prealloc
> 64

But what's the max value ?
cat /proc/asound/card0/pcm0p/sub0/prealloc_max

I've you compiled ALSA yourself, the default will be 64.
If you're using stock ubuntu, it will be 4MB, unless the card doesnt'
support that value.

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steven at openmedia

Jun 22, 2012, 3:21 AM

Post #9 of 10 (833 views)
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Re: Audio sync issued with DVBS, mythbunut 12.04 and mythtv 0.25 [In reply to]

On Thu, June 21, 2012 6:47 pm, Jean-Yves Avenard wrote:
> On 19 June 2012 18:03, Steven Ellis <steven [at] openmedia> wrote:
>> Just upgraded to 12.04 and I'm getting a different value
>>
>> cat /proc/asound/card0/pcm0p/sub0/prealloc
>> 64
>
> But what's the max value ?
> cat /proc/asound/card0/pcm0p/sub0/prealloc_max
>
> I've you compiled ALSA yourself, the default will be 64.
> If you're using stock ubuntu, it will be 4MB, unless the card doesnt'
> support that value.

Stock Ubuntu 12.04 with their build of MythTV. The myPVR bits simple map
over the top and don't adjust the kernel etc.

cat /proc/asound/card0/*/sub0/prealloc_max
32768
32768
32768

--------------------------------------------
Steven Ellis - Technical Director
OpenMedia Limited - The Home of myPVR
email - steven [at] openmedia
website - http://www.openmedia.co.nz

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jyavenard at gmail

Jul 7, 2012, 2:32 AM

Post #10 of 10 (731 views)
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Re: Audio sync issued with DVBS, mythbunut 12.04 and mythtv 0.25 [In reply to]

On 22 June 2012 20:21, Steven Ellis <steven [at] openmedia> wrote:
>
> cat /proc/asound/card0/*/sub0/prealloc_max
> 32768
> 32768
> 32768

Those aren't the default.. But the maximum the hardware allow.
cat /proc/asound/card0/*/sub0/prealloc

will give you the current value it's set at

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