Problems recording from DVB channel that has just come online

[gEd]

BBC3 and BBC4 start tranmission at 19:00. If I schedule a recording on one of these channels that starts at 19:00, gbpvr :-

starts the recording
stops the recording
starts the recording and finishes at the correct time
recording file in 0 bytes.

attached log showing example (gaffes galore was the show)

I suspect that the problem relates to the fact that gbpvr starts the recording <pre-pad minutes> early and fails to lock onto the signal.

[bgowland]

I suspect that the problem relates to the fact that gbpvr starts the recording <pre-pad minutes> early and fails to lock onto the signal.

Ah yes. That's a nasty one.

It's not a lack of signal but similar. The AV streams aren't broadcast until something like 30-60 seconds before they go live (I can't remember exactly).

About a year ago there was something that I wanted to record at the start of either BBC3 or 4 (can't remember). I eventually got to the bottom of it after several failed recordings by monitoring with TS Reader.

I can't remember if I posted a general warning here (I meant to). I guessed there was nothing that sub could easily do about it so didn't persue it as a support issue. In the end it came down to me and my wife trying to remember to set 0 minutes pre-padding on any recording that was the 'first of the day'.

Cheers,
Brian

[gEd]

Thanks Brian

I'll test with 0 mins pre-paddding tomorrow to verify that this works ok but I still find it curious how gbpvr handled this situation.

After starting the recording, it then stops it (after several attempts)
2008-04-19 18:58:05.062 VERBOSE BDARecorder::StartRecording() finished
2008-04-19 18:58:30.109 VERBOSE BDARecorder::StopRecording()
2008-04-19 18:58:30.109 VERBOSE StopRecording()@1
2008-04-19 18:58:30.359 VERBOSE StopRecording()@2
2008-04-19 18:58:30.359 VERBOSE StopRecording()@3
2008-04-19 18:58:30.359 VERBOSE StopRecording()@4
2008-04-19 18:58:30.359 VERBOSE StopRecording()@5
2008-04-19 18:58:30.359 VERBOSE StopRecording()@6
2008-04-19 18:58:30.359 VERBOSE StopRecording()@7
2008-04-19 18:58:30.359 VERBOSE StopRecording()@8

it then restarts the recording, reporting that the signal is ok when the station is now active.

2008-04-19 18:58:35.359 VERBOSE BDARecorder::StartRecording() finished
2008-04-19 18:59:35.500 VERBOSE checking signal stats took total: 78ms (1,1,71,100).....(,0,0,0)
2008-04-19 19:00:35.640 VERBOSE checking signal stats took total: 78ms (1,1,71,100).....(,0,0,0)
2008-04-19 19:01:35.796 VERBOSE checking signal stats took total: 63ms (1,1,71,100).....(,0,0,0)

but file length remains 0 bytes.

I thought that gbpvr used to detected if the file was 0 bytes, report "Recording is unusually small" and restart the recordng. I am curious as to why it didn't do it in this instance.

cheers

[sub]

To be honest, I'm not really sure how it'd cope with this situation. We dont have any part-time channels here, so its not an easy scenario to test.

[bgowland]

To be honest, I'm not really sure how it'd cope with this situation.

Would the second attempt to start the recording have gone through the process of trying to map the AV ES PIDs on the demux?

[sub]

Yes, each attempted recording should try to map the PIDs.

[bgowland]

OK - looking at the second attempt in gEd's log though, I'm fairly sure the AV streams still won't have been present.

2008-04-19 18:58:35.359 VERBOSE BDARecorder::StartRecording() finished

When I was looking at this last year, I seem to remember it was no more than 1 minute before transmission time that they came online.

I'll try to remember to do a test tomorrow at switchover.

[pBS]

just yank the feed, and plug it back in to simulate a channel coming online....
[ant/cable whatever]
i know that doesn't simulate exact circumstances but it'd give idea how it acts if just a plain lack of signal followed by a good signal while trying to record...

[sub]

Actually, that is not the same scenario at all. My understanding is that signal will be present and locked all a long, but some of the channels contained that transport stream stop and a certain time of day, and others start. The signal and data is there all day long, but the channels contained in that data may vary depending on the time of day you check.

[bgowland]

Yep - BBC3 and BBC4 share the same AV ES PIDs as CBBC and CBeebies. The SIDs are different but obviously a PES PID has to be unique on a given TS. I'd guess somewhere in digital TV land, someone allocated a fixed list of PES PIDs to the broadcasters to stop them treading on each other's toes.

To save bandwidth and pack some more part time channels in, it's easiest to switch off the main payload (AV) whilst still broadcasting private data streams for that channel, then re-use the AV PIDs for another channel.

All the part time channels are there 24/7 they just swap their AV streams around.

Cheers,
Brian