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

[Stephen Worthington]

On Mon, 28 Nov 2011 17:01:26 +1300, you wrote:

>> 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

I am using a Kingray SA164F splitter amplifier.  I got mine from Dick
Smith, but they do not seem to stock them any more.  The F versions
have F-connectors, which I prefer for my cables, but there are non-F
versions if you prefer Belling-Lee cables.  The F versions come with a
set of F to Belling-Lee converters if you have mixed cables.  There
are two and four way versions (SA162/SA162F or SA164/SA164F).