Saturday, 21 July 2007

Recording TV programs

With my new nVidia card installed I can now actually watch the videos I record. Capturing DVB-T streams is as easy as reading from /dev/dvb/adapter0/dvr0, at least with my CX23880 DVB card (cx88_dvb kernel module).

My next obstacle was finding a good scheduler. I tried DVR (Ubuntu's Feisty binary core dumps every time) and MythTV (can't get it to scan channels). Out of frustration I wrote an ugly hack to schedule and record some programs. I call it ("tive" is a pun on Tivo, but only works in Portuguese):

function usage() {
echo Missing parameters.
echo Usage:
echo $0 '"starting date/time" "seconds to record" "channel name"'

TZAP='tzap -r'

if [ -z "$WHEN" ]; then

at $WHEN >> __EOP__
# Sometimes /dev/dvb/adapter0/dvr0 "locks-up". Uncommenting the lines
# below will force the driver to be reloaded, thus ensuring that the
# device can be read.
#sudo /sbin/rmmod cx88-dvb cx8802 cx88xx cx88_vp3054_i2c
#sudo /sbin/modprobe cx88-dvb

$TZAP "$CHAN" > /dev/null 2>&1 &

echo tzap running under pid $PIDTZAP
cat $DVB > "$CHAN$WHEN.mpeg" &
echo Channel $CHAN being recorded under pid \$PIDCAT
echo Sleeping for $DURATION seconds
echo Stopping recording
kill \$PIDCAT
echo Stopping tzap
kill \$PIDTZAP
echo Finished

Say I want to record The Simpsons. I run

$ ./ "18:00 30.07.07" 2000 "TEN Digital"
warning: commands will be executed using /bin/sh
job 26 at Mon Jul 30 18:00:00 2007

The first parameter, "18:00 30.07.07", will be passed to at directly. The second, 2000, is how long to record for, around 33 minutes (probably not enough for TEN's crappy time-keeping). Finally, "TEN Digital" is the name of the channel, as expected by tzap and listed in ~/.tzap/channels.conf.

Some programs, The Simpsons included, are on 3:4 format, however the DVB-T stream is on 16:9 format (I don't know if this is always true). This causes the video to be captured with a pair of black bars on its side, which is annoying because it wastes space on your screen and hard-disk. One solution is to use mencoder to crop the video; I've put the (long) command in

if [ -z "$1" ]; then
echo Usage
echo $0 INPUT_FILE
echo File Cropped-INPUT_FILE will be created in the same path.

# Uncomment to preview cropped video
#mplayer -vf rectangle=530:576:95:0 "$1"

mencoder -msglevel all=4 -of mpeg -mpegopts format=dvd \
-srate 48000 -ofps 25 -ovc lavc -oac lavc -lavcopts \
keyint=15 -vf crop=530:576:95:0 "$1" -o Cropped-"$1"

Only one task remains: ad removal. I was hoping to use MythTV's commercials remover but at this point I was already quite frustrated with it so I went around looking for a video editing tool. And boy, did I try a lot of them - Lives seemed to be able to do what I wanted but it was unbearably slow for the big (~2-3Gb) mpeg files.

It took me a lot of time to finally find GOPDIT which, by the way, has Ubuntu binaries, works fine and fast. It is a bit hard to reach the right cut position because the scroller skips too much and the "go back frame" button stops working after a few clicks. However, given this was the only app I could find that did what I wanted, I was more than happy to donate some money to the author.

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