#!/bin/sh

# v4l-changechannel.sh <ch>

# Script to change channel on a v4l-capable tv-tuner.
# Use in mythtv-setup as external channel change command.
#
# It solves two problems I had with my saa7134-based
# Pinnacle PCTV Stereo (via both line-in and over PCI):
#
# - Tuner falling back to PAL-DK, even if once set
#   to PAL-BG. This would sometimes cause a very loud
#   static noise throughout the recording.
#   
# - When changing channel in MythTv or doing v4lctl
#   operations (like setting back PAL-BG), a loud
#   scratching noise would play for about a second.
#   Every recording I had would begin with a horrible
#   scratch before settling down to normal sound.
#
# Since even setting attribute 'mute' causes a really
# loud scratch, a different method is used to silence
# the tuner while changing channel. For that to work
# a file ~mythtv/.aumixrc must be present containing
# what you get by running aumix in interactive mode:
#
#   aumix -d /dev/mixer<tunermixer_no> -I
#
# and if you got working sound, then save the settings.
# My .aumixrc looks like this.
#
#   line1:100:100:P
#   line2:100:100:P
#   video:100:100:R     <--- this is where the sound is
#
# /LeL 2005

TVMIX="/dev/mixer1"
VIDEO="/dev/video0"
MUTED="3"             # seconds muted

# change to record sound from line1, but nothing's there -- i.e. mute
aumix -d $TVMIX -1 R
aumix -1 R

# now set whatever attributes we wish without crackling noises
v4lctl -c $VIDEO setchannel $1

v4lctl -c $VIDEO setattr 'mute' off
v4lctl -c $VIDEO setattr 'volume' 4
v4lctl -c $VIDEO setattr 'bright' 128
v4lctl -c $VIDEO setattr 'contrast' 68
v4lctl -c $VIDEO setattr 'color' 64

v4lctl -c $VIDEO setnorm PAL-BG

# change to record sound from video again -- i.e. unmute
# (do that by loading .aumixrc-settings with R on video)
sleep $MUTED && aumix -d $TVMIX -L && aumix -c R &