[mythtv-users] 0.25 Major AV sync problems

[Steven Ellis]

On Mon, June 18, 2012 6:03 pm, Steven Ellis wrote:
>
> On Sat, June 9, 2012 12:25 am, Richard wrote:
>> On 08/06/12 01:11, David Moore wrote:
>>> Thanks for the confirmations that I'm not the only one seeing this
>>> problem. FYI I have created a ticket #10797.
>>
>> I've done a little bit more testing but I can't say that I've managed to
>> home in on anything in particular.
>>
>> I'm using an NVidia 8400GS card and sound output via the on-board Intel
>> chipset.
>>
>> If I use the 'VDPAU Normal' profile, I get the problem.  If I switch it
>> just 'Normal', everything seems to be ok (apart from not looking as
>> nice).
>>
>> With audio set to SPDIF, I get the problem.  If I change audio to
>> analogue, I don't.
>>
>> When I get the problem, the A/V sync value seems to stay pretty much
>> fixed (maybe a little bit of jitter in the hundredths range), changing
>> either the video or audio settings to stop the problem and it changes
>> almost constantly.
>>
>> This is on my main box in the living room, running a fresh install of
>> Mythbuntu 12.04.
>>
>> I cannot reproduce the problem on my desktop.  It doesn't matter whether
>> what video or audio settings I use, everything stays in sync (I've no
>> way of listening to digital audio on the desktop but the A/V sync value
>> looks ok).  Both machines have the same NVidia card in them (at least,
>> it's the same chipset), but the desktop machine does have slightly newer
>> NVidia drivers.
>>
>> Here are the main differences:
>>
>> Mythbox
>> -----------
>> NVidia 295.40
>> 82801JI (ICH10 Family) HD Audio Controller
>> MythTV Version : v0.25.1
>>
>> Desktop
>> -----------
>> NVidia 295.53
>> 6 Series/C200 Series Chipset Family High Definition Audio Controller
>> MythTV Version : v0.25.1-1-g016db04
>>
>>
>> Does this give anyone any ideas?
>>
>
>
> I've upgraded from MythTV 0.23 to 0.25 and I'm seeing the issue on
> existing as well as new DVB-S MPEG-2 recordings with MP2 audio.
>
> I'm running a GT220 card with an M2NPV-VM board and an Athlon X2 5050BE
> CPU.
>
> I noticed that my de-interlacers were disabled during the upgrade so I've
> turned Advanced 2x back on. Display is generally 1920x1080 50Hz unless I'm
> watching US content.
>
> All my audio is going out over SPDIF to my amp. I haven't setup audio over
> HDMI yet with the new upgrade.
>
> In order to get any reasonable sync I need to exit playback and re-enter
> the file. Otherwise its a real mess.

Ok I think I have a fix. Checking logs I saw the following alsa error

Jun 17 20:30:10 mythtv mythfrontend[20861]: E CoreContext
audio/audiooutputalsa.cpp:545 (OpenDevice) ALSA: Unable to sufficiently
increase ALSA hardware buffer size - underruns are likely

and recommendation

Jun 17 22:36:39 mythtv mythfrontend[26876]: E CoreContext
audio/audiooutputalsa.cpp:213 (SetPreallocBufferSize) ALSA: Try to
manually increase audio buffer with: echo 128 | sudo tee
/proc/asound/card0/pcm1p/sub0/prealloc

I've actually bumped the prealloc up a bit higher to be certain

 echo 256 > /proc/asound/card0/pcm1p/sub0/prealloc

Just tested some files and sync is close to perfect and I'm not seeing any
audio centric errors.

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