[mythtv-users] mplayer -dumpstream better than myth record

Ben bluey at iguanaworks.net
Fri Sep 14 03:44:44 UTC 2007

On Thu, 2007-09-13 at 20:42 -0500, Kevin Kuphal wrote:
> On 9/13/07, Ben <bluey at iguanaworks.net> wrote:
>         I have two channels that I can record perfectly with mplayer
>         but not
>         with mythtv. Using the command
>         mplayer dvb://CHANNEL -dumpstream
>         I can then play the file back with mplayer (or whatever) and
>         it is
>         great. If instead, I have mythtv record the program, then when
>         I play it
>         back it is missing a lot of frames and jumps around and
>         sometimes cuts
>         on entirely. This happens if I play it back in mythtv-frontend
>         or with
>         mplayer.
>         Since I'm doing the playback with the same program (mplayer)
>         clearly,
>         the dump of the tv signal is different when recorded from
>         mythtv than
>         mplayer. Why? And this is only true on some channels... for
>         example, FOX 
>         has this problem, but ABC and NBC do not. These are HDTV
>         signals over
>         the air.
>         I have an air2pc card with 2.6.22 kernel (debian sid) and
>         myth-0.20.2.
>         All the channels receive >80% signal using dtvsignal.  My
>         first thought 
>         was that mplayer was using a different frequency than mythtv
>         was for the
>         channels. Looking at the mysql database, I see under
>         mythconverg/dtv_multiplex/frequency that for the channel in
>         question I'm
>         using the frequency 503000000 and mplayer
>         (in .mplayer/channels.conf) is 
>         using 503028615. So I changed the line in the sql database and
>         restarted
>         mythtv, but that didn't make a difference. I undid that change
>         and added
>         28615 to the mythconverg/channels/finetune but that too had no
>         effect. 
>         I'm stumped as to why saving the stream is different. Any
>         ideas? Both
>         mplayer and myth are running as unprivileged users without
>         suid or
>         anything.
>         It goes without saying, but live TV of these channels with
>         mythtv also 
>         doesn't work well, but "mplayer dvb://CHANNEL" is fine. And
>         finally, is
>         there a way to have mythtv-backend use mplayer to save
>         recording and
>         just circumvent whatever problem this is?
> Do you commflag your recordings?  If so, there is basically double the
> disk I/O happening.  Also, there is more going on when myth is
> recording (DB writes, etc) which also increase the I/O over what
> mplayer is doing with dumpstream.  Does your database share the same
> disk as your recordings? 

Interesting idea about the IO. I doubt it though. Here's why: I am not
doing commflag on my records (or any other processing). NBC is fine at
broadcasts in 1920x1080i and ~100Mb/min. FOX, which gives me mild
problems, broadcasts 1280x720p and 110MB/min. The station that gives me
the most problems, is MNT, which broadcasts at 1920x1080i and ~95Mb/min.
So I'm not seeing a correlation with rmy ecording problems and how much
it saves to the disk. I temporarily moved the recordings directory to a
different hard drive from the database, but it made no difference. Any
more ideas?


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