[mythtvnz] DVB-T recording artefacts after upgrade to Mythbuntu 11.10 with HVR2200

[David Shepherd]

> On Mon, 28 Nov 2011 14:42:49 +1300, you wrote:
>
>>> Hi,
>>>
>>> I use a DVB-T Hauppauge HVR-2200 to record FreeviewHD and play back
>>> with
>>> VDPAU. All was working fine with Mythbuntu 11.04 and then I upgraded to
>>> 11.10. (My first attempt was updating through Update Manager and that
>>> resulted in my system not booting any more, probably to do with some
>>> LightDM setting, but I ended up reinstalling from scratch.)
>>>
>>> Since we upgraded, we are getting intermittent strange visual artefacts
>>> in the recordings, where blockiness gets worse until it is bad enough
>>> that minutes of a program will be completely unwatchable and sound is
>>> distorted to the point that we can't understand it.
>>>
>>> The new features aren't that compelling, so if nobody has any ideas
>>> I'll
>>> just roll it back to the old Clonezilla image of 11.04 (I learnt that
>>> trick a while ago!!!)
>>>
>>> Thanks in advance,
>>>
>>> Aaron
>>>
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>>
>>Hmmm, this is interesting.  I'm getting exactly the same behaviour with
>> my
>>HVR-2200.  I'm in Auckland and have line of sight to SkyTower and
>>Waiatarua. I get the same symptoms on all 3 HD channels with my aerial
>>pointing to either transmitter.  Reception through my TV is perfect and
>>signal/quality are both 8+/10.  So I'm thinking it's HVR-2200 driver or
>>firmware or graphics related.
>>
>>The symptoms I see are exactly as you describe.  2-3 mins of
>> progressively
>>degrading video then audio.  Then it snaps back to perfect picture and
>>audio.  This pattern reoccurs at random intervals of 20-60 mins.
>>
>>If you flick back to your Clonezilla image of 11.04 and the problem goes
>>away, I'd be very interested in knowing which combination of HVR-2200
>>driver/firmware and graphics card your running.
>>
>>I'm running 0.24.1+fixes from the Debian Multimedia Stable repository on
>>top of Debian Squeeze with a stock 2.6.32 kernel.  VDPAU via a GT210 (bit
>>underpowered I know)
>>
>>Anyone else seeing same behaviour?
>>
>>Dave
>
> Those symptoms are of temporary bad reception causing a damaged
> recording.  I had that for a while until I installed an aerial
> amplifier.  If it is a damaged recording, then playing the damaged
> spot again will cause exactly the same symptoms.  If the problem is in
> the graphics drivers, I would expect that recordings made before the
> upgrade would suffer from the same problems as new recordings.  I have
> not had any problems playing files that were recorded on my main Myth
> box (11.04) on my laptop (11.10), so I expect that the graphics
> drivers are not the problem.  I do not use my laptop to record, so I
> do not know if I have any problems with recording on 11.10.
>
> One thing to try with a damaged file - when you have played past the
> damaged point in the file a bit, try skipping backwards a little bit.
> I have found that this can clear up the video and audio problems, as
> long as the place you go back to is after the damage has ended.  It
> looks as though Mythfrontend does not handle damage particularly well
> and can let it cause more visible and audible problems well past the
> actual damage, but going backwards causes it to recalculate things and
> get it right.
>
> It is likely that the point everything comes right again after damage
> is the point that there is a key frame in the file.  Key frames
> contain all the data needed to display a frame.  Non-key frames have
> to use the data from the previous frame(s) plus the current frame data
> to display a frame, so they can be contaminated by bad data from
> previous frames.  I am not sure how often key frames occur in TV H.264
> files, but it is fairly typical in generating compressed video files
> to force a key frame every one to ten seconds.  But I have seen them
> as much as one minute apart.
>
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>

Thanks for that info.  I'm pretty sure that I get the same behaviour at
the same point on multiple playbacks indicating a damaged file.  I do a
few tests tonight.  I'll also try the skip-back test you suggest.  Can you
give some make/model details on the aerial amplifer you installed?

Thanks
Dave