[LUAU] Re: Putting the UG back in LUG

[Eric Hattemer]

Matt Darnell wrote:
>> I just have to remember to play with the udev settings
>> after any major rpm upgrade.
>>     
> Not sure what that means....but I am sure some of the boys will!
>
>   
Oh, I should explain.  It's suggested that for simplicity sake, you
start by running mythbackend as root.  I did that for a while, then
decided it might be better/safer to run it as it's own unprivileged
user.  This meant that all of the devices the program needs need to be
accessible by the user that runs mythbackend.  By default, Fedora makes
the video capture cards only accessible by root, and the sound card
either by root, or the user logged into X11 on console.  I needed to
change that, so I played with their udev script, which sets the
permissions on a reboot.  Everytime I upgrade my rpms seriously, that
script gets overwritten.  I finally learned that I could make an addon
script with a higher number that wouldn't get overwritten, but I haven't
rebooted or upgraded since that.
> Wow that install guide is awesome!  The hardware guide is worth the price
> alone.
>
> Have you ever used the knoppix mythtv distro?  When you said FC4, I assume
> you built it from source.
>
>   
I haven't used the knopmyth, but I hear it almost surely works out of
the box with most hardware, quite well.  It might take some setup on
every reboot, but maybe you can store the settings on the hard drive.  I
don't know.
> I have an iMac for my machine at home...I wonder if you can stream to it.  I
> use 802.11g
>
>   
It probably won't be a big problem.  They worked out a mythfrontend for
OSX.  You can probably compile it with the Apple Developer Tools.  You
probably need to compile a whole bunch of libraries, install fink, or
hope they have a binary version.  I haven't looked at the Apple stuff,
though.  If you can find a mythtv/nuppelvideo decoder for your favorite
media player, then you don't need the mythfrontend to watch pre-recorded
stuff (you need a very special codec to watch live TV).  I believe the
standard codec pack for MPlayer comes with nuppelvideo.
> Thanks for the feedback!  Do you mind giving you hardware specs -
> motherboard part #, CPU, which bttv cap card.
>   
My old motherboard blew a set of capacitors.  I kept swearing that there
was a redhat kernel problem, because I'd get random panics once a week
or so.  I kept bugging Warren.  The redhat kernel specialist told me to
look at the motherboard.  Sure enough, there was brown goo oozing out of
most of my capacitors.

My new motherboard that I've had for a few months is the MSI K7N2GM-V.
The motherboard isn't really that important for this, unless you are
going for a shuttle setup.  A lot of people are using shuttles and via
processors for their mythtv machines because they are small and
passively cooled (quiet).  I don't care about either of those factors.

I'm using an Athlon XP.  I forget which PR number it is, but it's
1141MHz with 2252 bogomips.  I think it was an 1800+.  I put in 1GB of
RAM just for fun (I was ordering RAM for my Windows gaming machine, and
just wanted to grab some for the Linux machine too).

The TV card is an ATi TV Wonder PCI.  It was like $70 in the year 2000.
It has an onboard MPEG-1 encoder only (useless).  MPEG-1 takes up
massive amounts of space, so mythtv doesn't use MPEG1.  This means I
have to encode to some other video format, which uses the processor.  I
can get max quality mp3 with 640x480 180-quality RTJPEG using probably
around 60-70% CPU.  I only use DivX (MPEG4) anymore on low quality
stuff, and use 900kbit/sec rating.  I used to do mpeg4 encoding on the
fly on high quality stuff, but this ramped up the processor into the
danger zone.  If I run low on space, I can use the nice-19 transcoder
function to re-encode my rtjpeg stuff to divx over maybe the time it
would take for the show to run twice.  But I have a 250GB hard drive, so
that's not too much of a problem.  You should note, that you will want
outrageous amounts of disk space for your mythtv box.  I was thinking
about setting up a TB array.  But in the end, you start to realize that
the hard drive is just a buffer between the time you tape the show and
the time you watch it.  If your schedule is anywhat consistent, you will
need to eventually delete things without watching them if you tape too
much.  My divx 900kb/s shows are about 10MB/min (keep in mind the sound
gets added in).  The RTJPEG 480x320 at 160 stuff is about 40MB/min.  The
RTJPEG 640x480 at 180 stuff is just over 50MB/min.  That means an hour show
takes up about 3GB.  I could optimize these a bit, turn transcoding back
on, etc., but I haven't palyed with these in a while.  Since I got my
$3000 1080p TV (a week ago), I probably should ramp up all resolutions
to 640x480 (the max the card handles and the max SDTV comes in at).  The
divx 320x240 at 900kb/s looks pretty goofy when it's not on my 20"
monitor.  Maybe I'll up the res, but keep the bitrate the same.  Mostly
I just tape talk shows at this quality level, anyway.  It's just that at
the same bitrate, large frame sizes give good stills, and small frame
sizes give good motion.  If I did 640x480 at 900kb/s, I'd get insane
macroblocking.  But that's not relevant for talk shows.

With any of the cards with the MPEG2 encoders builtin, you can tape to
MPEG2 directly.  This uses negligible cpu (I think someone said about
4%).  Even at max quality, the shows don't take up an unreasonable
amount of space.  You can then run the transcoder in the background at
minimum priority (in mythtv, you setup a recording profile that
automatically transcodes certain shows you pick).  I think the Haupauge
150/250/350 cards are the most common ones with builtin MPEG2 encoders.
There are cards with 720p capabilities, but since I have SD cable, I've
never looked into that.

-Eric Hattemer