[mythtvnz] Pixelation/Corrupt recordings

[Stephen Worthington]

On Tue, 15 Jul 2014 14:17:42 +1200, you wrote:

>On 07/07/14 22:20, Stephen Worthington wrote:
>> It is always worth trying a cold boot if you suspect firmware
>> problems.  Shut down the PC, turn the power supply off, turn off all
>> peripherals, and wait for at least a minute for all the capacitors to
>> decay.  Turn the power supply on, and wait for 15 seconds or so for
>> the standby power to stabilise.  Turn on peripherals.  Then start the
>> PC.  That should ensure that absolutely all hardware is completely
>> reset and all firmware is reloaded.
>I'm not so sure now. I seem to have the latest firmware; the firmware I 
>manually extracted from the latest drivers matched anyway.
>
>> To help diagnose this, you might like to add the "-v record" option to
>> the end of your mythbackend command line (in
>> /etc/init/mythtv-backend.conf in Mythbuntu).  Then you will get extra
>> debug output logged about the recording process.
>Yes. I see errors now. Thanks for the tip. Here's a sample that seems to 
>transition from good to bad. Problems start around 7am
>
>$head -8000 mythbackend.log.1 | tail -2000 | pastebinit
>http://paste.ubuntu.com/7796380/
>
>
>> The "TVRec[20]" (and any other place where there is a number in [])
>> indicates the multirec tuner number that was used.  To find which
>> physical tuner that was, you can look it up in the database with some
>> SQL:
>>
>> select cardinputid,cardid,sourceid,inputname,displayname,(select
>> videodevice from capturecard where cardid=ci.cardid) as videodevice
>> from cardinput ci order by cardinputid;
>>
>> In the resulting table, the number in [] is the cardinputid value, and
>> the matching videodevice value is the physical tuner device used.
>This is a useful query. Thanks again for taking the time to give me such 
>a detailed response.
>
>I have more information now. None of it seems to help though:
>
>When watching live tv on the backend Myth cunningly shows signal 
>strength and s/n. Strength was alarmingly low. I happened to have an old 
>signal amplifier lying around from previous experimenting. Sadly it 
>doesn't pass anything into the GHz range, so no satelite. It did 
>significantly raise the signal level and, when I've checked, s/n is 
>around 90%.
>
>Most recordings are fine now. Sometimes they are totally unwatchable 
>though. And sometimes Myth fails to create any output.

It is possible to get too strong a signal and that causes problems
too.  But I would expect the card to be saying 100% signal level if
that was happening.

I do not at all understand there being no log output sometimes about a
problem.  There should be something, even if it is far back in history
where a tuner disappeared and Myth decided it could no longer even try
using it.  When you get a problem like that, it would be a good idea
to look at the ls -al /dev/dvb output to see if any tuners are
missing, and also to try other software to see if they can use the
tuners.  VLC or mplayer come to mind, and there are others.

>I live in an apartment with one coax connection. Everything outside is 
>beyond my control. However, the other couple of hundred people in the 
>building are presumably doing OK.

Is there someone else you can ask to see if they have problems too?
Preferably an apartment on the same floor as you so they are likely to
be sharing the same bit of cable that goes to your apartment.  Cable
problems in apartment blocks do happen - so maybe you need to talk to
whoever you are renting it from or to the body corporate to see if
there are any other people with problems.

>I've spent a bloody long time dicking around with this, but I'm a geek; 
>I will persist. I feel I'm running out of ideas though.
>
>In reading about signal amplifiers I encountered filters to remove LTE 
>signals. 2degrees has just launched 4g in Auckland. It seems unlikely 
>telcos would be allowed to cause out of band interference.
>
>I also encountered a long standing obscure cx88 i2c driver bug. I have 
>not tried the workaround on the master backend because it seemed to work 
>in the past. Maybe I'll give that a go too.

I am wondering if you need to get in some professional help.  A good
aerial company will have proper test meters and be able to install an
amplifier that should work properly if necessary, including the
satellite signals.  That would likely be cheaper than buying your own
aerial test meter as they seem to start at $700 or so for the cheapest
I have seen recently.

Or you might like to try buying a cheap (< $30) USB DVB-T or DVB-T2
tuner to see if it has the same problems or not.  That should resolve
whether it is the tuner card.  However, finding one with Linux support
is not always easy - the ones I used to recommend seem to have
disappeared from the market.  TradeMe usually has a good selection of
what is currently available, but the sellers often do no post enough
information to be able to look them up to see about Linux support.