[mythtv] Help diagnosing HD channel recording problem

Bob Rakosky brakosky at gmail.com
Sat Nov 25 20:41:06 UTC 2006


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
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