[mythtv-users] Video is behind audio, dropping frames to catch up (VDPAU, HD content)

[Joseph Fry]

On Thu, Feb 28, 2013 at 12:15 PM, Karl Newman <newmank1 at asme.org> wrote:

> On Thu, Feb 28, 2013 at 8:05 AM, Paul Gardiner <lists at glidos.net> wrote:
>
>> On 28/02/2013 15:39, Mike Perkins wrote:
>>
>>> On 28/02/13 12:15, Paul Gardiner wrote:
>>>
>>>> On 28/02/2013 12:01, Mike Perkins wrote:
>>>>
>>>>> On 28/02/13 08:23, Paul Gardiner wrote:
>>>>>
>>>>>> On 27/02/2013 22:04, Thomas Börkel wrote:
>>>>>>
>>>>>>> HI!
>>>>>>>
>>>>>>> I have now tried many things, but I am running out of ideas.
>>>>>>>
>>>>>>> * it happens usually every 2-10 minutes
>>>>>>> * it happens for HD h264 and SD MPEG2, just for HD a little more
>>>>>>> often
>>>>>>> * it happens with and without VDPAU
>>>>>>> * it happened on old and upgraded hardware (only sound card
>>>>>>> identical)
>>>>>>> * it happens on 0.26 and earlier versions
>>>>>>> * I have tried all VDPAU profiles
>>>>>>> * I have disabled logging over NFS (> /dev/null)
>>>>>>> * I have enabled realtime prio (but it is not mentioned in the log)
>>>>>>> * I have reniced mythfrontend to -2 and X to -12
>>>>>>> * I have set the GPU to max. frequency all the time, so no switching
>>>>>>> * I have disabled the often crashing mythlcdserver
>>>>>>> * I have tried different kernel and NVidia driver versions
>>>>>>>
>>>>>>> What else can I try? What more info should I provide?
>>>>>>>
>>>>>>> Probably, something needs a little CPU time every now and then and
>>>>>>> this
>>>>>>> probably causes that little "jump" in playback and the log entry from
>>>>>>> the subject, but I don't know what it is and why MythTV is so
>>>>>>> sensitive
>>>>>>> on such hardware specs (Core i3, 3.1 GHz)?
>>>>>>>
>>>>>>> Or does it probably have something to do with the fact that this is a
>>>>>>> diskless PXE frontend?
>>>>>>>
>>>>>>> Any hints would be greatly appreciated.
>>>>>>>
>>>>>>
>>>>>> None of the myth systems I've built have ever synchronized AV
>>>>>> correctly.
>>>>>> I've always had to pause and unpause every now and then to regain sync
>>>>>> and even then it's to get it to a consitentish 100ms which I then
>>>>>> correct within my AV receiver. It's odd, because every other player
>>>>>> I've
>>>>>> tried with my recordings or downloads show them correctly in sync.
>>>>>>
>>>>>>  My diskless PXE frontend has never had problems with AV sync. I use
>>>>> NFS
>>>>> to mount the root but not for media directories. On the other hand, my
>>>>> sound comes out the TV. Perhaps it is the "AV receiver" which is the
>>>>> common variable?
>>>>>
>>>>
>>>> I have wondered that. I will test, although several of the myth systems
>>>> I was referring to were connected direct to speakers, and the sync was
>>>> always variable and depended on the last user command. I think my
>>>> current frontend may be pretty much ok when I'm not using different
>>>> screen modes for different video resolutions, but I'm not sure of that.
>>>> Need to do more testing.
>>>>
>>>> What CPU are you running?
>>>>
>>>>  My current front end is one of these:
>>>
>>> http://www.newegg.com/Product/**Product.aspx?Item=**N82E16813131663<http://www.newegg.com/Product/Product.aspx?Item=N82E16813131663>
>>>
>>> That outputs via HDMI. A previous incarnation had a C7 VIA chip which
>>> output using VGA and 3.5 mm stereo into the TV. No problems either way.
>>>
>>
>> Nice. Will that do HQ scaling and Advanced 2x deinterlacing? Maybe I
>> should upgrade. In any case, you are using an Atom too, so the A/V
>> sync problem isn't down to processing power.
>>
>> Just realised that with my current set up, it will be difficult to
>> remove the AV receiver: it's my only AMP, and the TV has no speakers.
>> I can try moving to HDMI audio from spdif again, but last time I
>> tried that it made sync worse. I never have sync problems with
>> my blu-ray player, so I sort of doubt it is caused by the amp,
>> but I'd like to rule it out. I guess I just need to borrow a little
>> mobile speaker from someone.
>>
>> BTW, do you know what the "playback details" display measures A/V
>> sync in?
>>
>> P.
>>
>
> Some TVs can do video processing which can induce delay. Usually there's a
> setting or a mode which disables this (something like Game Mode should do
> it). This may not be the cause of your problem, but it might be worth
> looking into.


Indeed, if  you split your audio and video signal to different devices, you
are subject to any processing delays imposed by those devices.  I have seen
TV's that introduce well over 100ms of lag (a few whole frames of video)
with some settings.  The ability to adjust the sync is one feature I like
about mythtv that I believe is completely overlooked by most folks.  Even
with a high end BlueRay player feeding a top of the line TV and Audio
setup, you can end up with noticeably out of sync audio.
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