Heredoc commands for find . -exec sh {} + - loops

Question

I'm trying to convert a hierarcy of TIFF image files into JPG, and out of boredom, I want to do find and ffmpeg in a single file.
So I set find to invoke sh with the -s flag, like thins:
#!/bin/sh
export IFS=""
find "$#" -iname 'PROC????.tif' -exec sh -s {} + << \EOF
for t ; do
ffmpeg -y -v quiet -i $t -c:v mjpeg ${t%.*}.jpg
rm $t
done
EOF
However, there's just too many files in the directory hierarchy, and find chopped filename array into several small pieces, and sh -s was only succesfully invoked for the first argument chunk.
The question being: how could one feed such in-body command to every sh invocation in the find command?
Update
The tag "heredoc" on the question is intended for receiving answers that do not rely on external file or self-referencing through $0. It is also intended that no filename would go through string-array processing such as padding with NUL-terminator or newline, and can be directly passed as arguments.

Answer 1

The heredoc is being used as the input to find. I think your best bet is to not use a heredoc at all, but just use a string:
#!/bin/sh
find "$#" -iname 'PROC????.tif' -exec sh -c '
for t ; do
ffmpeg -y -v quiet -i "$t" -c:v mjpeg "${t%.*}.jpg" &&
rm "$t"
done
' sh {} +

Answer 2

I am re-writing your code below:-
#!/bin/bash
find "$1" -name "PROC????.tif" > /tmp/imagefile_list.txt
while read filepath
do
path=${filepath%/*}
imgfile=${filepath##*/}
jpgFile=${imgfile%.*}.jpg
cd "$path"
ffmpeg -y -v quiet -i "$imgfile" -c:v mjpeg "$jpgFile"
rm -rf $imgfile
done < /tmp/imagefile_list.txt
IF you don't want to change the current directory you can do it like below:-
#!/bin/bash
find "$1" -name "PROC????.tif" > /tmp/imagefile_list.txt
# If you list down all the .tif file use below command
# find "$1" -name "*.tif" > /tmp/imagefile_list.txt
while read filepath
do
path=${filepath%/*}
imgfile=${filepath##*/}
jpgFile=$path${imgfile%.*}.jpg
ffmpeg -y -v quiet -i "$filepath" -c:v mjpeg "$jpgFile"
rm -rf $imgfile
done < /tmp/imagefile_list.txt
rm -rf /tmp/imagefile_list.txt