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Problem playing last program before a channel stops broadcasting for the day (UK DVB-T)

 

 

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John.Veness.mythtv at pelago

Dec 12, 2010, 12:25 PM

Post #1 of 19 (2177 views)
Permalink
Problem playing last program before a channel stops broadcasting for the day (UK DVB-T)

Hi,

I have the following problem on a UK DVB-T (Freeview) setup, which
started when I upgraded to 0.24. I didn't have this problem in many
months of 0.22. I only ran 0.23 for a couple of days so don't know if it
occurred there.

A few channels on Freeview are not broadcast 24-hours. For example, Five
USA stops at 1am, and CBBC stops at 7pm. If I try to playback a
recording of the final program on a channel, i.e. one that ends at 1am
on Five USA or which ends at 7pm on CBBC, then the playback doesn't work.

Specifically, what I see is a blank (black) screen and no audio. I can
skip around the playback and press I and see an accurate progress bar,
but see/hear no content.

As far as I can tell, the programs are actually being recorded OK. I can
play back the raw files with mplayer, for example. And if I watch one of
the recordings while they are being recorded, they show fine. Something
seems to be happening that is causing Myth to not play back these
recordings when they are finished.

Most of the affected recordings have been made since 0.24, but I have
one recording that was made during the 0.22 days that is also exhibiting
this problem. This same recording played fine in 0.22, but no longer
plays in 0.24.

On affected recordings, the preview picture is also blank (although grey
rather than black). They also error if I try to do a lossless transcode
on them.

I record 3 minutes past the end of the scheduled time. I haven't yet
tried to see what would happen if I stop exactly when the channel ends.

Has anyone else seen this problem? Any suggestions for troubleshooting?
Shall I report this as a bug?

Cheers,

John

--
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J.Pilk at tesco

Dec 12, 2010, 1:27 PM

Post #2 of 19 (2128 views)
Permalink
Re: Problem playing last program before a channel stops broadcasting for the day (UK DVB-T) [In reply to]

On 12/12/10 20:25, John Veness wrote:
> Hi,
>
> I have the following problem on a UK DVB-T (Freeview) setup, which
> started when I upgraded to 0.24. I didn't have this problem in many
> months of 0.22. I only ran 0.23 for a couple of days so don't know if it
> occurred there.
>
> A few channels on Freeview are not broadcast 24-hours. For example, Five
> USA stops at 1am, and CBBC stops at 7pm. If I try to playback a
> recording of the final program on a channel, i.e. one that ends at 1am
> on Five USA or which ends at 7pm on CBBC, then the playback doesn't work.
>
> Specifically, what I see is a blank (black) screen and no audio. I can
> skip around the playback and press I and see an accurate progress bar,
> but see/hear no content.
>
> As far as I can tell, the programs are actually being recorded OK. I can
> play back the raw files with mplayer, for example. And if I watch one of
> the recordings while they are being recorded, they show fine. Something
> seems to be happening that is causing Myth to not play back these
> recordings when they are finished.
>
> Most of the affected recordings have been made since 0.24, but I have
> one recording that was made during the 0.22 days that is also exhibiting
> this problem. This same recording played fine in 0.22, but no longer
> plays in 0.24.
>
> On affected recordings, the preview picture is also blank (although grey
> rather than black). They also error if I try to do a lossless transcode
> on them.
>
> I record 3 minutes past the end of the scheduled time. I haven't yet
> tried to see what would happen if I stop exactly when the channel ends.
>
> Has anyone else seen this problem? Any suggestions for troubleshooting?
> Shall I report this as a bug?
>
> Cheers,
>
> John
>

I have seen the same thing; not recently, but that's probably because
nothing has been scheduled recently for end-of-service times. Since I
run virtually all my recordings through mythcutprojectx I just did that
- with no cutlist - and AFAIR they then played fine and could be edited
as normal. It's certainly inconvenient, and that workaround would
probably not improve the WAF: I'm not sure it's a bug.

I also used to have difficulties when a recording started before
start-of-service - BBC THREE and BBC FOUR both starting at 7pm - but
recently that doesn't seem to have been a problem either.

John P

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John.Veness.mythtv at pelago

Dec 13, 2010, 1:49 AM

Post #3 of 19 (2110 views)
Permalink
Re: Problem playing last program before a channel stops broadcasting for the day (UK DVB-T) [In reply to]

On 12/12/10 20:25, John Veness wrote:
> I record 3 minutes past the end of the scheduled time. I haven't yet
> tried to see what would happen if I stop exactly when the channel ends.

Last night I set CSI:NY to stop recording on channel Five USA at exactly
1am (which is when the channel goes off air), but it still had the
problem of being seemingly blank when played back in Myth. I guess there
might be a few seconds difference between my HTPC clock and when the
channel actually closes, so next I'll try stopping it a minute before
closedown.

Other than John Pilkington, has anyone else seen this?

Can any other UK DVB-TV viewers try recording the last program on a
channel, e.g. Jinx on CBBC Channel at 6.35pm to 7pm, or Cinemania on
Five USA tonight at 12.35am to 1am, especially if you add a couple of
minutes extra to the end time, and let the list know if you can play it
back or not?

Cheers,

John

--
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J.Pilk at tesco

Dec 13, 2010, 2:34 AM

Post #4 of 19 (2116 views)
Permalink
Re: Problem playing last program before a channel stops broadcasting for the day (UK DVB-T) [In reply to]

On 13/12/10 09:49, John Veness wrote:
> On 12/12/10 20:25, John Veness wrote:
>> I record 3 minutes past the end of the scheduled time. I haven't yet
>> tried to see what would happen if I stop exactly when the channel ends.
>
> Last night I set CSI:NY to stop recording on channel Five USA at exactly
> 1am (which is when the channel goes off air), but it still had the
> problem of being seemingly blank when played back in Myth. I guess there
> might be a few seconds difference between my HTPC clock and when the
> channel actually closes, so next I'll try stopping it a minute before
> closedown.
>
> Other than John Pilkington, has anyone else seen this?
>
> Can any other UK DVB-TV viewers try recording the last program on a
> channel, e.g. Jinx on CBBC Channel at 6.35pm to 7pm, or Cinemania on
> Five USA tonight at 12.35am to 1am, especially if you add a couple of
> minutes extra to the end time, and let the list know if you can play it
> back or not?
>
> Cheers,
>
> John
>
"Here's one I made earlier:"

> http://www.gossamer-threads.com/lists/mythtv/users/435907#435907

and I don't have a recording that's affected just now, but it just might
be worth trying an appropriately modified version of:

mythtranscode --mpeg2 --buildindex --showprogress --chanid 1002
--starttime 20101212205600

John P
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mythtv at mikeholden

Dec 13, 2010, 3:04 AM

Post #5 of 19 (2109 views)
Permalink
Re: Problem playing last program before a channel stops broadcasting for the day (UK DVB-T) [In reply to]

> On 13/12/10 09:49, John Veness wrote:
> Other than John Pilkington, has anyone else seen this?
>
> Can any other UK DVB-TV viewers try recording the last program on
> a
> channel, e.g. Jinx on CBBC Channel at 6.35pm to 7pm, or Cinemania
> on
> Five USA tonight at 12.35am to 1am, especially if you add a couple
> of
> minutes extra to the end time, and let the list know if you can
> play it
> back or not?

Haven't seen it myself, and my other half would certainly have
mentioned it if she had seen it!

I've set up the following for tonight:
CBBC - Jinx
BBC4 - Art of Germany
Film4 - Mutual Appreciation

Each is the last program before close.

I've given them a -5, 0 and +5 end time offset, so we'll see
tomorrow what happens. Each one is set to start at the correct time.
--
Mike Holden

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John.Veness.mythtv at pelago

Dec 13, 2010, 5:48 AM

Post #6 of 19 (2102 views)
Permalink
Re: Problem playing last program before a channel stops broadcasting for the day (UK DVB-T) [In reply to]

On 13/12/10 11:04, Mike Holden wrote:
> Haven't seen it myself, and my other half would certainly have
> mentioned it if she had seen it!
>
> I've set up the following for tonight:
> CBBC - Jinx
> BBC4 - Art of Germany
> Film4 - Mutual Appreciation
>
> Each is the last program before close.
>
> I've given them a -5, 0 and +5 end time offset, so we'll see
> tomorrow what happens. Each one is set to start at the correct time.

Thanks. In my experiments, the problem definitely occurs with the last
program on CBBC Channel and CBeebies and Five USA, but doesn't occur
with the last program on BBC3 and BBC4, so you might not see the problem
with "Art of Germany" tonight.

My hunch is that the trigger for the problem is when a channel shares a
DVB-T "slot" (sorry, I'm not sure of the correct technical term) with
another channel and things switch from one to another. As I understand
it, when CBBC and CBeebies finish, BBC3 and BBC4 immediately start in
their place. However, when BBC3 and BBC4 finish, there are often a few
hours until CBBC and CBeebies start, so the final program on one of
those channels isn't always affected. I'm also not sure if Film4 shares
with another channel, and if it does, whether there's an immediate
changeover or a gap of some hours, so I'm not sure if that one will be
affected either.

So if you can manage it, could test candidates would be:

CBBC - Jinx
CBeebies - CBeebies Bedtime Story
Five USA - Cinemania

Many thanks in advance,

John

--
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mail01 at iarmst

Dec 13, 2010, 5:54 AM

Post #7 of 19 (2105 views)
Permalink
Re: Problem playing last program before a channel stops broadcasting for the day (UK DVB-T) [In reply to]

On Monday 13 December 2010, John Veness wrote:
> On 12/12/10 20:25, John Veness wrote:
> > I record 3 minutes past the end of the scheduled time. I haven't yet
> > tried to see what would happen if I stop exactly when the channel ends.
>
> Last night I set CSI:NY to stop recording on channel Five USA at exactly
> 1am (which is when the channel goes off air), but it still had the
> problem of being seemingly blank when played back in Myth. I guess there
> might be a few seconds difference between my HTPC clock and when the
> channel actually closes, so next I'll try stopping it a minute before
> closedown.
>
> Other than John Pilkington, has anyone else seen this?

Still running 0.23-fixes here, but I've seen this same problem on several
occasions. I remember once watching a recording that was still in progress,
but the next morning the same recording would only show a blank screen. I also
allow a 3 minute overrun by default, so mythtv can still be recording when a
station goes off-air. I simply use a small script that does a lossless
transcode using ffmpeg to 'fix' the recordings.

--
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John.Veness.mythtv at pelago

Dec 13, 2010, 7:46 AM

Post #8 of 19 (2100 views)
Permalink
Re: Problem playing last program before a channel stops broadcasting for the day (UK DVB-T) [In reply to]

On 13/12/10 10:34, John Pilkington wrote:
> "Here's one I made earlier:"
>
>> http://www.gossamer-threads.com/lists/mythtv/users/435907#435907
>
> and I don't have a recording that's affected just now, but it just might
> be worth trying an appropriately modified version of:
>
> mythtranscode --mpeg2 --buildindex --showprogress --chanid 1002
> --starttime 20101212205600
>
> John P

Thanks for the link, John. That certainly sounds like the same issue. I
guess something changed in the DVB code between 0.22 and 0.23, as I
never saw this problem in 0.22 or earlier versions.

Unfortunately mythtranscode didn't seem to fix my recordings. I tried
both with and without --allkeys (using
http://www.mythtv.org/wiki/Repairing_the_Seektable#Using_mythtranscode
as a reference). I used --infile rather than --chanid and --starttime
but I don't think that should have made a difference.

After doing mythtranscode, I notice that if I try to play back the
recordings and press I, rather than having a timecode that looked pretty
much correct as I previously did (even though the screen was blank and
audio not present), it now seems to show a length of just one second, so
if anything, things seem to be a bit worse after trying that.

I also tried mythcommflag --file <filepath> --rebuild, by the way, but
that didn't help either.

nuvexport fails when trying to transcode the affected recordings to XviD
(other recordings are OK with nuvexport), and trying to run a lossless
transcode from the frontend also fails. Even if I could transcode, I
don't really want to, as I would lose the DVB-T subtitles (captions),
which I do use sometimes.

I've looked in active bugs in http://code.mythtv.org/trac/ but couldn't
see one that matched this, although I only looked at the summary line.
Does anyone know if there is a bug about this already? If not, I'll
raise one. Are there any mythtv devs reading this thread who might know
more about this?

Cheers,

John

--
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J.Pilk at tesco

Dec 13, 2010, 8:22 AM

Post #9 of 19 (2104 views)
Permalink
Re: Problem playing last program before a channel stops broadcasting for the day (UK DVB-T) [In reply to]

On 13/12/10 15:46, John Veness wrote:
> On 13/12/10 10:34, John Pilkington wrote:
>> "Here's one I made earlier:"
>>
>>> http://www.gossamer-threads.com/lists/mythtv/users/435907#435907
>>
>> and I don't have a recording that's affected just now, but it just might
>> be worth trying an appropriately modified version of:
>>
>> mythtranscode --mpeg2 --buildindex --showprogress --chanid 1002
>> --starttime 20101212205600
>>
>> John P
>
> Thanks for the link, John. That certainly sounds like the same issue. I
> guess something changed in the DVB code between 0.22 and 0.23, as I
> never saw this problem in 0.22 or earlier versions.
>
> Unfortunately mythtranscode didn't seem to fix my recordings. I tried
> both with and without --allkeys (using
> http://www.mythtv.org/wiki/Repairing_the_Seektable#Using_mythtranscode
> as a reference). I used --infile rather than --chanid and --starttime
> but I don't think that should have made a difference.
>
I just suggested that as a simple and probably harmless thing to try,
not through any real understanding of what might be happening; my script
has used it thousands of times. But ISTR there _is_ a difference between
the chanid, starttime call and the infile one. Maybe it's just the
paths they use. chanid starttime _does_ rebuild the seektable - at least
for recordings not suffering from some unknown problem!
1009_20101212215800.mpg translates to 1009 20101212215800 :-)

Cheers


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mythtv at mikeholden

Dec 14, 2010, 7:12 AM

Post #10 of 19 (2076 views)
Permalink
Re: Problem playing last program before a channel stops broadcasting for the day (UK DVB-T) [In reply to]

Mike Holden wrote:
>> On 13/12/10 09:49, John Veness wrote:
>> Other than John Pilkington, has anyone else seen this?
>>
>> Can any other UK DVB-TV viewers try recording the last program on
>> a
>> channel, e.g. Jinx on CBBC Channel at 6.35pm to 7pm, or Cinemania
>> on
>> Five USA tonight at 12.35am to 1am, especially if you add a couple
>> of
>> minutes extra to the end time, and let the list know if you can
>> play it
>> back or not?
>
> Haven't seen it myself, and my other half would certainly have
> mentioned it if she had seen it!
>
> I've set up the following for tonight:
> CBBC - Jinx
> BBC4 - Art of Germany
> Film4 - Mutual Appreciation
>
> Each is the last program before close.
>
> I've given them a -5, 0 and +5 end time offset, so we'll see
> tomorrow what happens. Each one is set to start at the correct time.

All 3 recorded correctly, and were playable this morning.

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John.Veness.mythtv at pelago

Dec 14, 2010, 7:39 AM

Post #11 of 19 (2097 views)
Permalink
Re: Problem playing last program before a channel stops broadcasting for the day (UK DVB-T) [In reply to]

On 14/12/2010 15:12, Mike Holden wrote:
> Mike Holden wrote:
>>> On 13/12/10 09:49, John Veness wrote:
>>> Other than John Pilkington, has anyone else seen this?
>>>
>>> Can any other UK DVB-TV viewers try recording the last program on
>>> a
>>> channel, e.g. Jinx on CBBC Channel at 6.35pm to 7pm, or Cinemania
>>> on
>>> Five USA tonight at 12.35am to 1am, especially if you add a couple
>>> of
>>> minutes extra to the end time, and let the list know if you can
>>> play it
>>> back or not?
>>
>> Haven't seen it myself, and my other half would certainly have
>> mentioned it if she had seen it!
>>
>> I've set up the following for tonight:
>> CBBC - Jinx
>> BBC4 - Art of Germany
>> Film4 - Mutual Appreciation
>>
>> Each is the last program before close.
>>
>> I've given them a -5, 0 and +5 end time offset, so we'll see
>> tomorrow what happens. Each one is set to start at the correct time.
>
> All 3 recorded correctly, and were playable this morning.

Thanks Mike. I suspect Jinx worked because you stopped recording 5
minutes before the end. In my experience, stopping the recording early
is a successful workaround, although of course it's a pain to tweak
rules to do that, especially on programmes which are shown at different
times of the day during the week (e.g. CSI:NY, which sometimes ends at
1am on Five USA when the channel goes off-air).

For the other two shows, as I mentioned on
http://www.gossamer-threads.com/lists/mythtv/users/464686#464686, I
think the problem only occurs when a DVB-T slot gets immediately reused
for another channel, which I know happens when Five USA, CBBC and
CBeebies goes off-air, but may not happen on BBC4 and Film4, so it may
be that those two particular shows weren't good candidates to
demonstrate the problem.

If you, or any other UK DVB-T (Freeview) users, are willing to help test
this tonight, good candidate test programmes would be:

CBBC - Jinx 18.35
CBeebies - CBeebies Bedtime Stories 18.50
Five USA - Cops In Crisis 00.45

To experience the problem, you should record, say, five minutes after
the normal stop time. You should find that the recording is not playable.

Or if you have sufficient tuners, and if you can persuade Myth to do so
(e.g. by adding a manual recording schedule), you could try recording
the same program simultaneously twice, one stopping five minutes before
the normal stop time, and one stopping five minutes after the normal
stop time. You should find that the recording that stops early is
playable, and the one that stops late is not.

Many thanks in advance.

Cheers,

John

--
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mail01 at iarmst

Dec 14, 2010, 9:11 AM

Post #12 of 19 (2084 views)
Permalink
Re: Problem playing last program before a channel stops broadcasting for the day (UK DVB-T) [In reply to]

On Tuesday 14 December 2010, John Veness wrote:
> On 14/12/2010 15:12, Mike Holden wrote:
> > Mike Holden wrote:
> >>> On 13/12/10 09:49, John Veness wrote:
> >>> Other than John Pilkington, has anyone else seen this?
> >>>
> >>> Can any other UK DVB-TV viewers try recording the last program on
> >>> a channel, e.g. Jinx on CBBC Channel at 6.35pm to 7pm, or Cinemania
> >>> on Five USA tonight at 12.35am to 1am, especially if you add a couple
> >>> of minutes extra to the end time, and let the list know if you can
> >>> play it back or not?
> >>
> >> Haven't seen it myself, and my other half would certainly have
> >> mentioned it if she had seen it!
> >>
> >> I've set up the following for tonight:
> >> CBBC - Jinx
> >> BBC4 - Art of Germany
> >> Film4 - Mutual Appreciation
> >>
> >> Each is the last program before close.
> >>
> >> I've given them a -5, 0 and +5 end time offset, so we'll see
> >> tomorrow what happens. Each one is set to start at the correct time.
> >
> > All 3 recorded correctly, and were playable this morning.
>
> Thanks Mike. I suspect Jinx worked because you stopped recording 5
> minutes before the end. In my experience, stopping the recording early
> is a successful workaround, although of course it's a pain to tweak
> rules to do that, especially on programmes which are shown at different
> times of the day during the week (e.g. CSI:NY, which sometimes ends at
> 1am on Five USA when the channel goes off-air).
>
> For the other two shows, as I mentioned on
> http://www.gossamer-threads.com/lists/mythtv/users/464686#464686, I
> think the problem only occurs when a DVB-T slot gets immediately reused
> for another channel, which I know happens when Five USA, CBBC and
> CBeebies goes off-air, but may not happen on BBC4 and Film4, so it may
> be that those two particular shows weren't good candidates to
> demonstrate the problem.

Film4 doesn't have a consistent finish time (does it actually go off-air?). I
just checked a recording from a few days ago & with the extra time added for
an overrun, it cut off during a series of interviews which were not listed in
the epg & running after the last scheduled show.

Haven't tried recently, but Quest always used to trigger this problem for me.

--
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John.Veness.mythtv at pelago

Dec 15, 2010, 8:26 AM

Post #13 of 19 (2054 views)
Permalink
Re: Problem playing last program before a channel stops broadcasting for the day (UK DVB-T) [In reply to]

On 14/12/2010 17:11, Ian Armstrong wrote:
> Film4 doesn't have a consistent finish time (does it actually go off-air?). I
> just checked a recording from a few days ago& with the extra time added for
> an overrun, it cut off during a series of interviews which were not listed in
> the epg& running after the last scheduled show.
>
> Haven't tried recently, but Quest always used to trigger this problem for me.

Looking at
http://en.wikipedia.org/wiki/List_of_digital_terrestrial_television_channels_%28UK%29,
Film4 actually broadcasts 24 hours, even if for some of those hours it
is a blank screen, so recording the "last" program on this channel
probably won't show the described problem.

The best candidate channels to try this on are the ones that that page
say "timeshares" with others, avoiding BBC Three and BBC Four as they
often have a gap after the final program finishes before they switch to
CBBC/CBeebies, e.g.:

- CBBC Channel
- CBeebies
- Dave
- Dave ja vu
- Fiver
- Five USA
- Quest

Can any UK DVB-T viewers successfully playback a recording of the final
program of the day on any of those channels, with a few minutes added to
the stop time? I cannot in 0.24, although I could in 0.22.

Sorry to bang on about this, but before I raise a bug I would like to
see a little more confirmation that it's not just me, or indeed, if
anyone *can* playback such a recording, then it would be interesting to
compare the differences between setups.

Cheers,

John

--
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mail01 at iarmst

Dec 15, 2010, 10:50 AM

Post #14 of 19 (2052 views)
Permalink
Re: Problem playing last program before a channel stops broadcasting for the day (UK DVB-T) [In reply to]

On Wednesday 15 December 2010, John Veness wrote:

> The best candidate channels to try this on are the ones that that page
> say "timeshares" with others, avoiding BBC Three and BBC Four as they
> often have a gap after the final program finishes before they switch to
> CBBC/CBeebies, e.g.:
>
> - CBBC Channel
> - CBeebies
> - Dave
> - Dave ja vu
> - Fiver
> - Five USA
> - Quest
>
> Can any UK DVB-T viewers successfully playback a recording of the final
> program of the day on any of those channels, with a few minutes added to
> the stop time? I cannot in 0.24, although I could in 0.22.
>
> Sorry to bang on about this, but before I raise a bug I would like to
> see a little more confirmation that it's not just me, or indeed, if
> anyone *can* playback such a recording, then it would be interesting to
> compare the differences between setups.

Still on 0.23-fixes here, but I did a test this morning with a short recording
from both Community & BBC3 (BBC3 ends @ 5.30am). Both fail to play within
mythtv, but can be played with both xine & mythtv.

I just did a test with CITV & the same happens. I was better prepared this
time, so some more information.

I started the recording 5 minutes before CITV went off air. 2 minutes later I
started playback on a frontend & paused it. I started playback on a second
frontend, but didn't pause it. Both of these ran without problems. However
when I attempted playback on a third frontend 1 minute after the station went
off-air, playback failed. The two frontends that were already playing were
fine & I could pause, unpause, and skip around the recording, but once I
exited playback I could no longer restart it, with mythtv just showing a blank
screen. As before, xine & mplayer can play the recording.

--
Ian
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mail01 at iarmst

Dec 16, 2010, 3:41 AM

Post #15 of 19 (2039 views)
Permalink
Re: Problem playing last program before a channel stops broadcasting for the day (UK DVB-T) [In reply to]

On Wednesday 15 December 2010, John Veness wrote:

> Sorry to bang on about this, but before I raise a bug I would like to
> see a little more confirmation that it's not just me, or indeed, if
> anyone *can* playback such a recording, then it would be interesting to
> compare the differences between setups.

I've done some more hunting & think I may have found something. When the
channel goes off-air the program map table changes. This is embedded in the
recording & mythtv seems to use this off-air table instead of the earlier on-
air one. As a result, although mythtv sees the video & audio streams that
we're interested in, it discards them in preference of whatever streams
remain. In my case it discards the MPEG2VIDEO, MP3 and DVB_SUBTITLE streams &
proceeds to playback the single DSMCC_B stream that replaces them.

--
Ian
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nospam312 at gmail

Dec 16, 2010, 3:56 AM

Post #16 of 19 (2040 views)
Permalink
Re: Problem playing last program before a channel stops broadcasting for the day (UK DVB-T) [In reply to]

> I've done some more hunting & think I may have found something. When the
> channel goes off-air the program map table changes. This is embedded in the
> recording & mythtv seems to use this off-air table instead of the earlier on-
> air one. As a result, although mythtv sees the video & audio streams that
> we're interested in, it discards them in preference of whatever streams
> remain. In my case it discards the MPEG2VIDEO, MP3 and DVB_SUBTITLE streams &
> proceeds to playback the single DSMCC_B stream that replaces them.

Unless things have been fixed you also get a similar problem if you
start recording a programme before the channel starts broadcasting.

e.g. if the recording rule starts a few minutes early (in case the
programme starts early) it will attempt to record but nothing is even
when the channel starts broadcasting.

I suspect if the program map table changes when the channel goes
off-air the program map table also changes when the channel starts to
broadcast.

This is a particular problem for UK Freeview as quite a few channels
are not on 24hours a day and if Myth schedules a recording and it
happens to be the first programme of the day on a channel it fails.

Apologies if this has been fixed in 0.24.
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John.Veness.mythtv at pelago

Dec 16, 2010, 2:06 PM

Post #17 of 19 (2029 views)
Permalink
Re: Problem playing last program before a channel stops broadcasting for the day (UK DVB-T) [In reply to]

On 16/12/10 11:41, Ian Armstrong wrote:
> I've done some more hunting& think I may have found something. When the
> channel goes off-air the program map table changes. This is embedded in the
> recording& mythtv seems to use this off-air table instead of the earlier on-
> air one. As a result, although mythtv sees the video& audio streams that
> we're interested in, it discards them in preference of whatever streams
> remain. In my case it discards the MPEG2VIDEO, MP3 and DVB_SUBTITLE streams&
> proceeds to playback the single DSMCC_B stream that replaces them.

Thanks for the discovery. For what it's worth, I have opened a new
ticket about this issue, http://code.mythtv.org/trac/ticket/9384

Cheers,

John

--
John Veness, MythTV user, UK, DVB-T
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mail01 at iarmst

Dec 16, 2010, 2:08 PM

Post #18 of 19 (2040 views)
Permalink
Re: Problem playing last program before a channel stops broadcasting for the day (UK DVB-T) [In reply to]

On Thursday 16 December 2010, nospam312 wrote:
> > I've done some more hunting & think I may have found something. When the
> > channel goes off-air the program map table changes. This is embedded in
> > the recording & mythtv seems to use this off-air table instead of the
> > earlier on- air one. As a result, although mythtv sees the video & audio
> > streams that we're interested in, it discards them in preference of
> > whatever streams remain. In my case it discards the MPEG2VIDEO, MP3 and
> > DVB_SUBTITLE streams & proceeds to playback the single DSMCC_B stream
> > that replaces them.
>
> Unless things have been fixed you also get a similar problem if you
> start recording a programme before the channel starts broadcasting.
>
> e.g. if the recording rule starts a few minutes early (in case the
> programme starts early) it will attempt to record but nothing is even
> when the channel starts broadcasting.

The only problem I've noticed with the first show, is that my one wireless
frontend tends to timeout when attempting to start playback. Other recordings
are fine.

> I suspect if the program map table changes when the channel goes
> off-air the program map table also changes when the channel starts to
> broadcast.

Yes, it does change.

> This is a particular problem for UK Freeview as quite a few channels
> are not on 24hours a day and if Myth schedules a recording and it
> happens to be the first programme of the day on a channel it fails.
>
> Apologies if this has been fixed in 0.24.

With 0.23-fixes, starting the frontend with the '-v libav,extra' option
reveals the necessary info. I imagine the 0.24 would be similar if someone
wishes to check.

Attempting to play a test recording, which crosses into the off-air time at
the end, shows the following (most output snipped to keep readable, just the
basic bits here):

mpegts_add_stream: stream #0, has id 0x26d and codec MPEG2VIDEO, ...
mpegts_add_stream: stream #1, has id 0x26e and codec MP3, ...
mpegts_add_stream: stream #2, has id 0x26f and codec MP3, ...
mpegts_add_stream: stream #3, has id 0x270 and codec DVB_SUBTITLE, ...

mpegts_remove_stream 0x270
mpegts_remove_stream 0x26f
mpegts_remove_stream 0x26e
mpegts_remove_stream 0x26d

mpegts_add_stream: stream #0, has id 0x272 and codec DSMCC_B, ...

Input #0, mpegts, from 'myth://192.168....
Duration: N/A, start: 46021.088289, bitrate: 15128 kb/s
Stream #0.0[0x272], 1/90000: Data: 0x0000

The video, audio & subtitle streams are added, but then removed. One data
stream is then added in their place, but being the only stream remaining
mythtv attempts to play it for entire duration of the recording instead of the
actual video & audio streams. The result is a blank screen with no audio.

--
Ian
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mythtv-list at dinkum

Dec 17, 2010, 12:13 AM

Post #19 of 19 (2008 views)
Permalink
Re: Problem playing last program before a channel stops broadcasting for the day (UK DVB-T) [In reply to]

On 16 Dec 2010, at 23:08, Ian Armstrong wrote:
>>
>> e.g. if the recording rule starts a few minutes early (in case the
>> programme starts early) it will attempt to record but nothing is even
>> when the channel starts broadcasting.
>
> The only problem I've noticed with the first show, is that my one wireless
> frontend tends to timeout when attempting to start playback. Other recordings
> are fine.

I've found that a too early recording (BBC3 etc.) will play ok with a few fwd skips (not ff) but the frame rate detection doesn't work correctly, I get a 50hz show played on a 60hz display. I guess the detection is done at the start of the file and for mheg only 60hz is as good a choice as 50hz, would be nice if the default frame rate was taken from the ntsc/pal selection in the database but I don't have a patch for that.

>
>> I suspect if the program map table changes when the channel goes
>> off-air the program map table also changes when the channel starts to
>> broadcast.
>
> Yes, it does change.

The sids are the same for video & audio across the shared channels so the mapping is the only thing that changes.

And not all freeview STBs get it right either, with some it's necessary to change channel and back for the video to appear, others if left on a shared channel after closedown will continue to show video and audio from the other shared channel with mheg graphics over the top.

Andre
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