Recording Video and Sound with Bttv

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# D. Recording Video and Sound with Bttv

In addition to the applications referenced in Section 5, recording can be managed from the command line. The issues discussed here with regard to sound capture deal only with the default kernel-2.6 and higher sound system: the Advanced Linux Sound Architecture.

The easy part is grabbing the video, for which we will use streamer, available with the Xawtv suite. Sound is another matter, however. You will need to access your mixer settings using amixer, the ALSA command-line mixer that should be available in the ALSA-tools package available from your Linux distributor. See man amixer to follow the command line options.

Your recording can be managed either using your primary soundcard if you have your Bt8x8 audio output connected to a mixer conduit that allows for capture (e.g. the 4-pin analog CDROM input slot), or the Bt8x8 card itself using the btaudio module. The following steps utilize the latter. First, identify the individual cards on your system (requires `/proc` filesystem):

       $ cat /proc/asound/pcm
       00-00: Intel ICH : NVidia CK8S : playback 1 : capture 1
       00-01: Intel ICH - MIC ADC : NVidia CK8S - MIC ADC : capture 1
       00-02: Intel ICH - IEC958 : NVidia CK8S - IEC958 : playback 1
       01-00: Bt87x Digital : Bt87x Digital : capture 1
       01-01: Bt87x Analog : Bt87x Analog : capture 1

The first column indicates the system numbering of your available sound devices, i.e., card 0 is the soundcard and card 01, or 1, is the Bt8x8.

Next, identify the mixer controls for the Bt8x8 card.

       $ amixer -c 1 controls
       numid=3,iface=MIXER,name='Capture Source'
       numid=2,iface=MIXER,name='Capture Boost'
       numid=1,iface=MIXER,name='Capture Volume'

Then identify the item settings of each:

       $ amixer -c 1 cget name='Capture Source'
       numid=3,iface=MIXER,name='Capture Source'
       ; type=ENUMERATED,access=rw---,values=1,items=3
       ; Item #0 'TV Tuner'
       ; Item #1 'FM'
       ; Item #2 'Mic/Line'
       : values=1

       $ amixer -c 1 cget name='Capture Boost'
       numid=2,iface=MIXER,name='Capture Boost'
       ; type=BOOLEAN,access=rw---,values=1
       values=on

       $ amixer -c 1 cget name='Capture Volume'
       numid=1,iface=MIXER,name='Capture Volume'
       ; type=INTEGER,access=rw---,values=1,min=0,max=15,step=0
       : values=0

Use cset for the capture source:

       $ amixer -c 1 cset name='Capture Source' 0

...and to set the volume:

       $ amixer -c 1 cset name="Capture Volume' 15

...and you should be ready.

Now try to record something:

       $ streamer -p 4 -t 1:00 -r 24 -q -o test.avi -j 90 -f mjpeg -F mono16

...and you should be recording a sound-enabled avi file. Press [Ctrl]-C to cancel early. Next step is to automate the recording for your very own home-brewed Tivo™!

I offer the following script as an example program for automating recording; you can copy and paste it into a file and make it executable (chmod u+x record-tv.sh).

| This script (and any recording from your Bttv device for that matter) generates extremely large files, on the order of several GB per hour, so be sure you have lots of free disk space available.

     #!/bin/bash
     # ================= record-tv.sh  ============================
     # = copyright 2003 by Greg Watson  gwatsonATlinuxlogin.com   =
     # = GPL2 License, minor modifications by Howard Shane        =
     # = hshaneATaustin.rr.com , under same license               =
     # = usage record-tv.sh prefix-filename record-time channel   =
     # = Example:  ./record-tv.sh enterprise 61:00 20             =
     # ============================================================
     # Version 0.9
     # Last Mod: Wed Feb 20 11:27 CST 2005

     # Output directory
     OUTPUT=$HOME/vcr
     # Streamer location
     STREAMER=/usr/bin/streamer
     # Alsa Mixer
     AMIXER=/usr/bin/amixer
     # v4lctl path
     V4LCTL=/usr/bin/v4lctl
     # Capture Volume to ensure sound is recorded (80%)
     CAPTURE_VOLUME=100

     # Tvtime settings file for color/brightness/contrast values
     TVTIME=$HOME/.tvtime/tvtime.xml

     # End of Config
     ###############

     # check if I'm running TV, if so just exit
     if [ `ps -C tvtime | grep -c tvtime` -gt 0 ]; then
             echo "TVtime is running, aborting recording."
             exit
     fi

     # If the filename prefix wasn't given, set it to 'recording'
     if [ -z $1 ]; then
             PREFIX="recording"
     else
             PREFIX=$1
     fi

     # if time is blank, record for 30 minutes
     if [ -z $2 ]; then
             TIME="30:00"
     else
             TIME=$2
     fi

     if [ ! -z $3 ]; then
             $V4LCTL setchannel $3
     fi

     # Check for vcr dir
     if [ ! -x $OUTPUT ]; then
             mkdir $OUTPUT
     fi

     DATE=`date +%m-%d-%Y-%H:%M`

     # Set the AC97 volume to 0 (so we don't hear the sounds)
     # Get mixer values first
     PLAY_VOL=`$AMIXER -c 0 cget name='Master Playback Volume' | grep : | sed 's/^.*=\([^,]*\).*$/\1/'`
     CAP_VOL=`$AMIXER -c 0 cget name='PCM Playback Volume' | grep : | sed 's/^.*=\([^,]*\).*$/\1/'`
     #
     $AMIXER -c 0 -q cset name='CD Playback Volume' 100
     $AMIXER -c 0 -q cset name='Capture Volume' 1

     # if tvtime.xml is set, then grab settings out of it
     if [ -f $TVTIME ]; then
             CONTRAST=`cat ${TVTIME} | grep DefaultContrast | sed 's/^.*value="\([^"]*\).*$/\1/'`
             BRIGHTNESS=`cat ${TVTIME} | grep DefaultBrightness | sed 's/^.*value="\([^"]*\).*$/\1/'`
             COLOR=`cat ${TVTIME} | grep DefaultColour | sed 's/^.*value="\([^"]*\).*$/\1/'`
             HUE=`cat ${TVTIME} | grep DefaultHue | sed 's/^.*value="\([^"]*\).*$/\1/'`

             $V4LCTL bright ${BRIGHTNESS}% color ${COLOR}% contrast ${CONTRAST}% hue ${HUE}%
     fi

     $STREAMER -p 4 -q -t ${TIME} -r 24 -q -o ${OUTPUT}/${PREFIX}-${DATE}-${TIME}.avi -j 90 -f mjpeg -F mono16

     # Sometimes streamer doesn't always re-mute audio, mute it again just to be sure
     $V4LCTL volume mute on

     # Restore volumes
     $AMIXER -q cset name='Master Playback Volume' $PLAY_VOL
     $AMIXER -q cset name='PCM Playback Volume' $CAP_VOL
     #
     # EOF

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