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

Ian Armstrong mail01 at iarmst.co.uk
Thu Dec 16 22:08:04 UTC 2010

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.


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