if you have a linux I made this script (ToH2364.sh) which look for all avi file and convert only the ones using divx3 codecs (msmpeg4) it could help
./ToH264.sh RootPathOfTheSearch extensionToLookFor ExtentionOfTheEncodedFile CodecToCheck
example
./ToH264.sh /media/HDD/ avi mp4 msmpeg4
but only the directory is mandatory so it could simply be:
./ToH264.sh /media/HDD/
#!/bin/bash
# erease result file
echo "Result File" > ToH264.result
#Get the forlder to search
fld="$1"
#Get the extension to look for if it exist, else look for "avi"
if [[ $2=="" ]]
then exti="avi"
else exti=$2
fi
#Get the futur extension for if it exist, else set "mp4"
if [[ $3=="" ]]
then exto="mp4"
else exto=$3
fi
#Get the codec to look for if it exist, else look for "msmpeg4"
if [[ $4=="" ]]
then cdc='msmpeg4'
else cdc=$4
fi
# exe the search and save the result in TpH264.tmp
find $fld -name "*.$exti" > ToH264.tmp
#convert each result stored in the file ToH264.tmp if it use the specified codec and if the output file doesn't exist
while read line
do
if avprobe -show_streams "$line" | grep $cdc
then
echo "$line" >> ToH264.result
no | avconv -threads 8 -i "$line" -c:v libx264 -crf 20 -c:a copy "${line%.*}.$exto"
fi
done < ToH264.tmp