Scripted fade in/out of audio

[dgmm]

All,

Are there any programs out there which can do fade in and out of audio during 
a copy or encode, under control of a shell script or similar?

I have a large number of short video clips which need to be re-encoded into 
one long stream with a one second fade-in at the start of each clip and a one 
second fade out at the end of each clip.

So far, I've got a script which separates audio and video and creates the 
fade-in/out for the video, re-encodes it and muxes the audio back in.
(I'm sure the script as is could be improved, advice welcome :-)

Would this be better on another list?  If so, which?

#! /bin/sh
# fader 0.1 - 29/01/07 - Dave Gallagher
#   Auto add 1sec fade-in/fade-out to avi clips
#  No error checking, files hard coded while testing
clip="/home3/billsvids/MaxQuality/CanadaEdits/101Greenland.avi"
pictype=png
frames=`tcprobe -i "${clip}" | grep V: | sed -e 's/\[avi.*es=//' -e 's/,.*//'`

vbitrate=`mplayer -identify -frames 0 "${clip}" |\
 grep ID_VIDEO_BITRATE |\
 sed -e 's/.*RATE=//'`

vbitrate=$(($vbitrate / 1000))
echo Frames="${frames}"
echo Video Bitrate="${vbitrate}kbps"

echo "------------------------------"
echo " Extracting audio"
echo "------------------------------"
mplayer -msglevel all=-1 -benchmark -vc null -vo null -dumpaudio \
 -dumpfile zaudio.mp3 "${clip}"

echo "---------------------------------------"
echo " extract frames"
echo "---------------------------------------"
if [ $pictype = jpg ] ; then
  echo Doing JPeG ; ptype="jpeg:quality=100"
else
  echo Doing PNG  ; ptype="png:z=0"
fi
mplayer -benchmark -nosound -vo "${ptype}" "${clip}"

#process frames to fade up from 0% brightness to normal
count=1
while [ $count -le 25 ] ; do
  sframe=`echo $count | awk '{printf("%8d",$0)}' | sed 's/ /0/g'`.${pictype}
  fadein=$(($count * 4))
#Might as well count backwards from the end too and fade out
  end=$(($frames - $count))
  eframe=`echo $end | awk '{printf("%8d",$0)}' | sed 's/ /0/g'`.${pictype}
  echo $sframe $eframe $fadein
  mogrify $sframe -modulate $fadein $sframe
  mogrify $eframe -modulate $fadein $eframe
  count=$(($count + 1))
done

# VERY HIGH QUALITY
video="-ovc lavc -lavcopts vcodec=mpeg4:mbd=2:mv0:\
trell:v4mv:cbp:last_pred=3:predia=2:dia=2:vmax_b_frames=2:\
vb_strategy=1:precmp=2:cmp=2:subcmp=2:preme=2:qns=2"
# VERY FAST
video="-ovc lavc -lavcopts vcodec=mpeg4:mbd=2"
bitrate="vbitrate=1200"

for j in "turbo:vpass=1 -nosound" "vpass=2 ${audio}" ; do
  mencoder -force-avi-aspect 4:3 -oac copy -audiofile zaudio.mp3 \
  -mf fps=25:type=$pictype "mf://*.$pictype" \
  ${video}:${bitrate}:${j} -ffourcc DX50 -o z1video.avi
done

if [ $pictype = jpg ] ; then
  rm *.jpg
else
  rm *.png
fi
rm zaudio.mp3
mplayer z1video.avi

-- 
Dave