[mythtv-users] unencrypted QAM scanner and dynamic channel insertion

[Andrew Kuan]

On 5/25/06, Andrew Kuan <askuan at gmail.com> wrote:
>
> I hacked together a script that scans my cable feed for unencrypted QAM
> channels and then does the following:
>
>    1. Creates a channels.conf file and plops it into the .mplayer
>    config directory
>       - 0:565778200:QAM_256:161:164:10
>       - 1:619780900:QAM_256:113:116:7
>       - 2:625781200:QAM_256:0:0:7
>       2. Grabs a single frame as a jpeg and copies it to a folder on
>    my web page for browsing
>    3. Inserts new channel and dtv_multiplex records:
>       - insert into dtv_multiplex
>       (mplexid,sourceid,frequency,modulation,symbolrate,polarity,sistandard)
>       values (91,5,619780900,'qam_256',0,'v','atsc')
>       - insert into channel
>       (chanid,channum,freqid,sourceid,callsign,name,mplexid,serviceid,atscsrcid)
>       values (5901,901,901,5,'TMPCHANO1','TMPCHANO1',91,7,0)
>
> I'm running into a few strange problems though.
>
> First off, the records I insert can't quite be tuned by MythTV for some
> reason. The OSD will say "LAm Partial Lock" when I tune to one of these
> channels and I get nothing. I can't seem to find any documentation on how to
> interpret what that means. Can someone point me to where some doco for the
> DVB OSD resides or explain what I'm doing wrong on those inserts?
>
> Second off, because of the above problem, I use mplayer as a backup. I can
> fire up one of these channels like this: "mplayer dvb://1" and sometimes it
> works just fine. But for some shows mplayer has a terrible time dealing with
> the channel's sound/A52 encoding and dies every few minutes. I'm certain
> this isn't a CPU issue but rather a sound decoder problem since it only ever
> uses 5% CPU while it's displaying one of these shows and mplayer never barfs
> when I use the "-nosound" setting.
>
> I'd welcome any suggestions on how to fix either problem -- including
> using some software other than MythTV or mplayer to view these channels. I'm
> also happy to describe and share the script (the hack that it is) if
> anyone's interested.
>
> Thanks!
>
> Andy
>

I tried playing with the MySQL channel and dtv_multiplex table entries for
these "extra" channels. For instance, after doing a scan one time, channel
and dtv_multiplex entries were inserted. When I tried to tune to the new
channel, I ended up with the OSD showing "LAm Partial Lock". So, just for
grins, I looked at the serviceid for the new channel and found a working HD
channel that had the same serviceid. I then looked up this working channel's
associated mplexid and copied the frequency from the working channel's
dtv_multiplex entry to the new channel's dtv_multiplex entry.

This time, I tuned to the new channel and I got a sign -- the wrong one, of
course -- but a lock nonetheless. This all leads me to believe that Myth
must have some issue with these random unencrypted QAM channels that I'm
pulling off my cable feed.

Which, as before, leads me back to the same question: is there a media
player with a working and robust AC3/A52 decoder out there? I'm trying out
vlc, but it's really a much more involved tool than I want.
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