[mythtv] Help diagnosing HD channel recording problem

Bob Rakosky brakosky at gmail.com
Tue Nov 28 17:15:07 UTC 2006


On 11/28/06, Mark Paulus <mark.paulus at verizonbusiness.com> wrote:
>
>
>
> Bob Rakosky wrote:
> > I've been trying to diagnose a problem that I've (always) been
> > experiencing with one of the high-def QAM channels I'm getting from my
> > cable provider.  I'm not convinced that the problem isn't with the
> > CableCo feed, but I'm starting to suspect that there is something in
> > Myth's recording logic that isn't quite right.
> >
> > First, some basic info.  I'm using a HDHomeRun tuner connected to the
> > cable system.  Running SVN version 11820 (current as of this AM).  My
> > cable feed has one channel (the local CBS digital channel) that is the
> > only channel on one of the QAM transports, which is the one that is
> > causing me problems.  The following lines show the channel info for this
> > transport, using hdhomerun_config (aliased as the "hr" command below):
> >
> > bobr at morris:~/tmp$ hr get /tuner0/status
> > ch=qam256:699000000 ss=87 snq=90 seq=100 bps=38809216 pps=0
> > bobr at morris:~/tmp$ hr streaminfo 0
> > program 13: 0.0  filter="0x0000 0x0030 0x0800 0x0801"
> >
> > This looks good, so far.  If I tune to this channel and set the filters,
> > fire up VLC and set the hdhomerun target for the tuner to the VLC's
> > network port, I get the video feed correctly.  Doing the same thing, but
> > using netcat and saving the stream to a file, the file will play back
> > correctly using Myth's internal player routines (via MythVideo).
> >
> > However, setting up a recording for this channel in Myth, I get an MPEG
> > file that Myth won't play.  Neither will VLC (nor various other MPEG
> > players) that I've tried on both Linux and Windows boxes).  However (and
> > this is a little weird), I can load the same MPEG file into avidemux,
> > set avidemux to save an MPEG TS file, and save the video (without doing
> > anything else), and I get a resulting MPEG file that will play fine in
> > both VLC and MythVideo.
> >
> > Attached is a snippet from my myth backend log with -v record,channel
> > for a 1-minute manual recording, as well as the output I got when I ran
> > the command "vlc -v 2 4080_20061125131500.mpg >vlcout1.txt 2>&1".
> >
> > Note that the other high-def channels that I can get from the cable feed
> > work fine.  However, those channels are packaged differently in that
> > they are multiplexed on a couple of other QAM channels, as evidenced by
> > the following commands/output:
> >
> > bobr at morris:~/tmp$ hr get /tuner1/status
> > ch=qam256:729000000 ss=98 snq=70 seq=100 bps=38807712 pps=0
> > bobr at morris:~/tmp$ hr streaminfo 1
> > program 4: 25.2 WEEK-SD filter="0x0000 0x0032 0x0880 0x0881"
> > program 3: 19.1 WHOI-DT filter="0x0000 0x0030 0x0800 0x0801"
> > program 1: 25.1 WEEK-HD filter="0x0000 0x0031 0x0840 0x0841"
> >
> > The CBS channel is the only "singleton" channel that I get.
> >
> > I'm kind of at a loss as to how to further debug this problem (and not
> > particularly familiar with the MPEG data structures or spec).
> >
> > Suggestions (or other assistance) would be nice.  If you want, I
> > will/can move this to the -Users list, but felt that it was more
> > appropriate for the -dev list.
> >
> >  -- Bob
> >
>
> I don't know if I can help, but perhaps you could try a couple of
> additional diagnostics that might help:
> What does tcprobe show about the saved file?
> what does TSReaderLite (http://www.coolstf.com/tsreader/) show about the
> saved file?
>
> Perhaps some more info about your captured file would be helpful.
>
> --
> Mark Paulus
> 2424 Garden of the Gods Rd  | Phone:  v622-5578 / 719-535-5578
> 0419/117 - LEC Access ; D5-1010   | FAX:    719-535-1665
> Colo Springs, CO  80919    | 1800PageMCI / 1406052
> AIM : mgpaulus1    /  sametime : mark.paulus
>
>
>
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>
>
>
> Thanks for the response.  The "quick" result is that tcprobe doesn't
really show anything -- I get the following:

 bobr at morris:~/tmp$ tcprobe -i 4080_20061125131500.mpg -H 120 -d 255
 [tcprobe] MPEG transport stream (TS)
 (ts_reader.c) Pids: 0x801 0x800 0x30 0x0
 [tcprobe] summary for 4080_20061125131500.mpg, (*) = not default, 0 = not
detected
    no audio track: use "null" import module for audio

which is exactly what I get (with different PIDs)  with a "known" good HD
file recorded by Myth.

It looks like the TSReader program might yield better info, but it will take
me a while to absorb it (like I said, I'm not at all familiar with the MPEG
specs, so I have a bit of a learning curve to tackle).


 -- Bob
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