[mythtv-users] Occasional missed recordings

Håkon Alstadheim hakon at alstadheim.priv.no
Fri Dec 12 08:33:29 UTC 2008

Michael T. Dean wrote:
> On 12/11/2008 10:15 PM, Tom Dexter wrote:
>> On Thu, Dec 11, 2008 at 9:47 PM, Tom Dexter wrote:
>>> I know that in the past there have been several here including me that
>>> have discussed occasionally missing recordings...where the backend
>>> logs look as though everything's fine but the file simply isn't there,
>>> and the watch recordings screen shows it as 0 GB.
>>> I have this once in a great while but tonight it happened on both The
>>> Office and 30 Rock on NBC (OTA DTV).  In both cases the log looked
>>> like this:
>>> 2008-12-11 21:00:02.982 Started recording: The Office "Moroccan
>>> Christmas": channel 1041 on cardid 2, sourceid 1
>>> 2008-12-11 21:00:03.544 TVRec(1): Changing from None to RecordingOnly
>>> 2008-12-11 21:00:03.552 TVRec(1): HW Tuner: 1->1
>> Wow...the same thing happened on ER at 10PM.
>> 5 minutes into it there was still no file.  Again, after deleting the
>> (non-exiting) recording I was able to record it fine by going into
>> LiveTV, tuning it in, and hitting record.  Actually all three of these
>> were on card 2 of my three HD-5500s.  After these shows record I'll
>> make sure that cards actually working ok, though I think it is.
> I've seen this happen where the problem was the broadcast stream.  I got 
> an episode of Terminator: TSCC, but Prison Break (which airs right after 
> T:TSCC on Fox) didn't record and gave a 0-byte file.  When I watched 
> T:TSCC, the station was flipping between their digital feed and their 
> analog feed, the captions were completely broken (in both the digital 
> and the analog-converted-to-digital-and-upscaled portions), and at 
> several places, the video completely disappeared (though audio remained).
> I would have first suspected my setup except for the issues in the 
> stream and the fact that a friend who also records OTA saw the exact 
> same thing happen.
> Watch the portions you did record and see if their garbage.  If so, 
> garbage in = garbage results.
> (No, I'm not saying that if someone properly fixes Myth to identify that 
> there has been an issue with starting the recording/receiving data that 
> I would be against it, but just trying to give a possible reason for the 
> failure.  And, since properly fixing Myth to identify... is a /lot/ of 
> work, I don't expect anything is going to happen to change it in the 
> near future.)
I've seen various things related to "bad reception" making an entire 
recording useless. I'm not capable of implementing such a check (yet), 
but if anyone reading this feels up to the task, here are some 
suggestions for checks that might be good (say after 30 and 60 seconds):

 - 0 length recording
- recording without sound
- recording without image

The checks would have to be implemented in different ways for analog and 
digital. Enabling the checks might mean we would need to be able to mark 
channels as "audio only" or "video only".

If the cause of problems is weak reception, the course of action for 
analog channels (at least on my setup) is making sure the box is lightly 
loaded before retuning. For digital the course of action is also 
stopping and re-starting the recording. 0 length recordings might also 
be caused  by things like a disk suddenly going missing, so this is not 
quite as simple as it seems, even without factoring in the complexity of 
the existing source-code.

There is also the case of analog stereo, which on my setup is REALLY 
annoying if the signal is weak. I had to make a script to enter som 
options to modprobe, stop myth, unload/reload the driver modules, and 
restart myth. Having myth detect that condition would probably be a bit 
too hackish though :-)
s p a m t r a p : finnesikke at alstadheim.priv.no

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