Greg's MythTV for Underpowered CPUs Page

Getting Started

This is what I have for hardware. Yes, the machine is really that under powered!

• Case/System: HP Pavillion 4445
• CPU: Pentium Celeron, 367 MHz
• RAM: 128 MB total. 2x64MB PC66
• Hard Drive(s): hda = Seagate AT34233A 4.3 GB drive, hdc = Western Digital WD1200JB-00GVA0 120 GB. The first harddrive was the original drive for the machine. I used this drive exclusively until I knew this whole experiment was going to work out. There was no sense in buying a 120 GB drive for a failed science experiment.
• CD/DVD Player/Burner: hdd = Lite-On SOHW-1613S (a Wal-Mart "limited quantity" advertisement in early November 2004).
• Video Capture: Hauppauge PVR-350.

Getting Extra Memory

# /sbin/chkconfig --level 2345 cups off
# /sbin/chkconfig --level 2345 pcmcia off

/root/.xinitrc

twm &
sleep 4
cd /usr/share/mythtv
mythfrontend

/etc/rc.local

/sbin/modprobe ivtv
/sbin/modprobe ivtv-fb
/sbin/modprobe lirc_i2c
export HOME=/root
cd /usr/share/mythtv
mythbackend &
startx

/etc/ntp.conf

Headaches along the Way

• A soundcard that wouldn't initialize.
• An ethernet card that died. A new ethernet card that wasn't supported by 2.6. Finally, I settled on a card that worked and was supported.

Compiling MythTV

Building DVDs without Running Transcode

To use native transcoding on a low-end CPU means delays. The time it takes to transcode a half-hour episode of a TV into a SVCD is measured in days (not hours or minutes). Whatever you do, you don't want to reencode video on a low-end box. So, the next thing I wanted to do was to be able to burn things from .nuv files to something that is DVD-compatible (or at least mostly so). This took a couple nights to figure out. The basic approach is outlined in section 21.18 of Installing and using MythTV. There are, however, a couple glitches.

First, the current version of MythTV with published binaries is 0.16. On-screen editing with this version hangs the front end. So, I needed to recompile the version in CVS (this is oh so much fun on a Celeron 367 with 128 MB of RAM...). In addition to that, I wanted to be able to do this from a command line (ssh-ed into the box).

Once everything was set up, here's the process I use to make a DVD of one show/episode/movie from my MythTV box.

• Use on-screen editing within MythTV to make your cutpoints to edit your recording however you see fit. Three rules seem to apply:
  • Even if you don't want the first part of the recording, leave the first second in. For whatever reason, if the first part of the movie is clipped, dvdauthor will curse at you with a number of "WARN: Skipping sector, waiting for first VOBU..." It also seems to mess with mplex's ability to synchronize the final cut. The last thing you want is output that looks like a bad 70's kung-foo movie dubbed from English into English. The casual observer may not notice this, but it will drive you CRAZY.
  • After a lot of experimentation, I found that a +150 millisecond shift works best to get audio and video synchronized by mplex. This is different than the +66 millseconds reported by tcprobe from within mpeg2cut. Go figure.
• Log into the MythTV box and run nuvexport, select the object you want to recut.
• Author the object you want back into a DVD format using the script found in section 21.18 of the guide.
• Burn a DVD of the DVD files using steps 7, 8 and 9 found in section 21.19 of the guide.
• Enjoy.

There does seem to be some discussion elsewhere that 480x480 videos are not DVD standard compliant. While this may be true, of the three DVD players in the house, they all seem to take the input and run.

mux.sh

#!/bin/sh
#
# mux.sh
#
# Mux audio and video after nuvexport runs.
#
# See http://hawley.homeip.net/recycled-machine-mythtv.html#authoring
# for more explanation.
#
# (c) 2004 Greg Hawley
#
# This script is derived from the MythTV documents.
#
# See 21.18 of http://www.mythtv.org/docs/mythtv-HOWTO-21.html

# usage:  mux.sh mp2file m2vfile mpeg_file

START=`date`

# The 150 millisecond shift is specific to a PVR-350 running
# under MythTV.  Your mileage may vary tuning this constant is
# up to the user.
nice -n 19 mplex -O +150ms -f 8 -V -o $3 $1 $2

END=`date`

echo Started at $START.
echo Ended at   $END.

mux+create+burn.sh

#!/bin/sh
#
# Mux audio and video after nuvexport runs.  Then create and burn a DVD.
#
# See http://hawley.homeip.net/recycled-machine-mythtv.html#authoring
# for more explanation.
#
# (c) 2004 Greg Hawley
#
# This script is derived from the MythTV documents.
#
# See 21.18 of http://www.mythtv.org/docs/mythtv-HOWTO-21.html

# usage: mux+create+burn.sh  mp2file m2vfile DVDdir

START=`date`

mkfifo dvdmpg

# negative values shift video in front of audio
# positive values shift video behind audio
nice -n 19 mplex -O +150ms -f 8 -V -o dvdmpg $1 $2 &
nice -n 19 dvdauthor -o $3 -f dvdmpg
nice -n 19 dvdauthor -o $3 -T

rm dvdmpg

growisofs -Z /dev/cdrom -dvd-video $3

END=`date`

echo Started at $START.
echo Ended at   $END.

MythTV Manual MySQL Queries -- Looking for Shows You Want to Record

I went off an figured out the MySQL query that MythWeb submits. As you'll see, it's a little ugly. From there, I created a little shell script that takes the results of the query and make a small web page. With that I created a crontab entry to automatically run the query daily building the web page I see. It's a bit of a hack, but it's also better than manually typing things into MythWeb.

First, below is the query. At the very end, you can see the stuff that really matters. Modify it as you see fit.

foo2.sql

SELECT program.chanid, program.starttime, program.title, program.subtitle
FROM program 
  LEFT JOIN programrating USING (chanid, starttime) 
  LEFT JOIN record ON  (
    (record.type = 5 AND program.title = record.title AND 
     record.chanid = program.chanid AND 
     record.starttime = SEC_TO_TIME(time_to_sec(program.starttime)) AND 
     DAYOFWEEK(record.enddate) = DAYOFWEEK(program.endtime))  
    OR (record.type = 4 AND program.title = record.title)  
    OR (record.type = 6 AND program.title = record.title)  
    OR (record.type = 3 AND program.title = record.title AND record.chanid = program.chanid) 
    OR (record.type IN (7, 8) AND program.title = record.title AND 
        record.chanid = program.chanid AND 
        record.starttime = SEC_TO_TIME(TIME_TO_SEC(program.starttime)) AND 
        record.startdate = FROM_DAYS(TO_DAYS(program.starttime)))  
    OR (record.type = 2 AND program.title = record.title AND 
        record.chanid = program.chanid AND 
        record.starttime = SEC_TO_TIME(TIME_TO_SEC(program.starttime)) AND 
        record.endtime = SEC_TO_TIME(TIME_TO_SEC(program.endtime)))  
    OR (record.type = 1 AND program.title = record.title AND 
        record.chanid = program.chanid AND 
        record.starttime = SEC_TO_TIME(TIME_TO_SEC(program.starttime)) AND 
        record.startdate = FROM_DAYS(TO_DAYS(program.starttime)))) 
  LEFT JOIN recordingprofiles ON record.profile=recordingprofiles.id  
WHERE 
(
  (program.title LIKE '%heavy%metal%' OR program.subtitle LIKE '%heavy%metal%')
  OR
  (program.title LIKE '%buckaroo%' OR program.subtitle LIKE '%buckaroo%')
  OR
  (program.title LIKE '%cool%hand%' OR program.subtitle LIKE '%cool%hand%')
  OR
  (program.title LIKE '%shawshank%' OR program.subtitle LIKE '%shawshank%')
  OR
  (program.title LIKE '%battlestar%' OR program.subtitle LIKE '%battlestar%')
  OR
  (program.title LIKE '%modern%marvels%' OR program.subtitle LIKE '%modern%marvels%')
  OR
  (program.title LIKE '%megastructures%' OR program.subtitle LIKE '%megastructures%')
  OR
  (program.title LIKE '%doctor%who%' OR program.subtitle LIKE '%doctor%who%')
  OR
  (program.title LIKE '%columbo%' OR program.subtitle LIKE '%columbo%')
  OR
  (program.title LIKE '%bicycle%racing%' OR program.subtitle LIKE '%bicycle%racing%')
  OR
  (program.title LIKE '%repo%man%' OR program.subtitle LIKE '%repo%man%')
)
GROUP BY program.title, program.starttime ORDER BY program.title, program.starttime;

run_query.sh

#!/bin/sh
#
# run_query.sh
#
# Run a manually generated mythtv query and generate a web page
# with the results.
#
# See http://hawley.homeip.net/recycled-machine-mythtv.html#trolling
# for more explanation.
#
# (c) 2005 Greg Hawley

FILE=/var/www/html/results.html
QUERY=/root/bin/foo2.sql
echo "<html>" > $FILE
echo "<head>" >> $FILE
echo "<title>Quick MythTV Query</title>" >> $FILE
echo "</head>" >> $FILE
echo "<body>" >> $FILE
echo "<h1>Quick MythTV Query</h1>" >> $FILE
echo "<h2>Query Runtime</h2>" >> $FILE
date >> $FILE
echo "<h2>Results</h2>" >> $FILE
echo "<pre>" >> $FILE
mysql -t -u mythtv -pmythtv mythconverg < $QUERY >> $FILE
echo "</pre>" >> $FILE
echo "<h2>Query Text</h2> >> $FILE
cat $QUERY >> $FILE
echo "</body>" >> $FILE
echo "</html>" >> $FILE

crontabfile

# add to cron with:
# crontab crontab
# check with:
# crontab -l crontab
12 07 * * * /root/bin/runquery.sh > /dev/null 2>&1

Querying for Actors, Directors, Writers, etc.

Things That Bug Me

• The bug in 0.16 that keeps editing from working (overcome).
• Fan noise.
• Quick extraction (without recoding) of MPEG files to remove commercials (overcome).
• Tuner frequency errors. I seem to get ghosting from other channels and noise from what may be tuner frequency inaccuracies. My PVR-350 has one of the newer LG tuners. This could be a driver error. I need to investigate.

Performance

MythDVD

• Compile mplayer with the ivtv patches that come with Chris Kennedy's ivtv releases.
• Use the following command to run the DVD:
  ivtvfbctl /dev/fb0 -alpha 0; mplayer -vo ivtv dvd://; ivtvfbctl /dev/fb0 -alpha 255

Contact

Copyright

Copyright (c) 2004-2005 Greg Hawley