Corrupted mpeg-4 files when trying to put recording and pulling screenrecord videos in script - bash

Question

I want to write a script that initiates adb shell screenrecord in the background of my looping script. The looping script will be waiting at a menu waiting to read a 1 character user input.
When user presses any key, I want to automatically stop the screen-recording and pull the video file onto the user's computer.
On top of that, I will need to be able to place a countdown timer that will display on screen once the screenrecording commences, so they know how close to the 3min limit they are;
..using printf "\r%*s" ((0)) "$remainingTime" in a for loop for example.
This is the general idea of what I'm trying to do:
fileName="rec.$$.mp4"
record(){
adb shell screenrecord /sdcard/$fileName &
read -n 1 -s -r -p ''
#EOF represents where the screenrecord command expects the EOF signal
EOF
}
extract(){
adb pull sdcard/$fileName
}
record | wait && extract
exit
Using this method to interrupt the screenrecord (when replacing EOF with either return or kill "$childPID") may be the problem, but I cannot find anywhere how to accomplish the EOF interrupt to avoid corrupting the video file produced.
Right now, it does interrupt with EOF replaced, and it does also pull the file, but the pulled file is always corrupted.
Any ideas?
I tried adding wait 's and using various interrupt types to replace the EOF signal but to no avail.
This produces identical results; corrupted video file.
#!/bin/bash
set -x; clear
fileName="rec.$$.mp4"
record(){
adb shell screenrecord /sdcard/$fileName & childPID=$!
read -n 1 -s -r -p ''
kill "$childPID"
wait "$childPID"
}
extract(){
adb pull sdcard/$fileName
}
record | wait && extract; exit
Replacing the kill command with exit produces identical results as well.

Answer 1

After reading the character, kill the background process and wait for it to finish
fileName="rec.$$.mp4"
adb shell screenrecord /sdcard/"$fileName" &
childpid=$!
read -n 1 -s -r -p '' endRec
kill "$childpid"
wait "$childpid"
adb pull /sdcard/"$fileName"
Rather then using abd pull, just pipe the screenrecord to your file and save it on the fly.
fileName="rec.$$.mp4"
adb shell screenrecord - > "$fileName" &
childpid=$!
read -n 1 -s -r -p '' endRec
kill "$childpid"
wait "$childpid"
I have verified that manually entering the screenrecord command and using the EOF signal to interrupt the screenrecord command,
Create a fifo and send it.
tmpd=$(mktemp -d)
fifo="$tmpd/fifo"
mkfifo "$fifo"
adb shell screenrecord /sdcard/"$fileName" < "$fifo" &
childpid=$!
read -n 1 -s -r -p '' endRec
echo -e '\04' > "$fifo"
wait "$childpid"
rm -r "$tmpd" # cleanup
adb pull /sdcard/"$fileName"
Alternatively a bash coprocess could be good here.

Answer 2

Success! After much trial and error, I figured out a method to send eof to the screenrecord function running on the device's shell!
The solution was to trap traditional signals, and have the script send adb shell echo \04 whenever the exitScript function is called (note that is also the function that the most common signals will execute when caught).
#!/bin/bash
set -x; clear
fileName="rec.$$.mp4"
# make sure SIGINT always works even in presence of infinite loops
exitScript() {
trap - SIGINT SIGTERM SIGTERM SIGSTOP # clear the trap
adb shell echo \04; extract; exit
}; trap exitScript SIGINT SIGTERM SIGSTOP # set trap
record(){
adb shell screenrecord /sdcard/$fileName
}
extract(){
adb pull sdcard/$fileName
}
record && extract
exitScript
I also believe that not running screenrecord in a subshell might've helped to avoid corrupting the output file.
After making the screenrecord function loop until an interrupt occurs (then extracting in the background for continuous video sequences), and putting everything in a function to plug into my script, I think issue is fully resolved. Thanks for all your help!
#!/bin/bash
screenDVR(){
clear
read -r -p 'Enter the file path (or just drag the folder itself) of where you want to save the video sequences.. ' savePath
if [ ! "$savePath" = "" ]; then cd ~; cd "$savePath"; else printf "\nDefaulting to home directory\n"; cd ~; fi
# remove all files on device containing 'rec.'
adb -d shell rm -f *"/sdcard/rec."*
# make sure SIGINT always works even in presence of infinite loops
exitScript() {
trap - SIGINT SIGTERM SIGTERM # clear the trap
tput cnorm
adb -d shell echo \04; wait
extract
# remove all files on device containing 'rec.'
adb -d shell rm -f *"/sdcard/rec."*; wait
exit
}; trap exitScript SIGINT SIGTERM # set trap
extract(){
printf "\n%*s\n" $((0)) "Extracting.. $fileName .. to your computer!"
wait && adb pull sdcard/$fileName || return
}
record(){
printf "\n\n%*s\n\n" $((0)) "Use CTRL-C to stop the DVR.."
while true; do
tStamp="$(date +'%Hh%Mm%Ss')"
fileName="rec.$tStamp.$$.mp4"
printf "\n%*s\n\n" $((0)) "Starting new recording: $fileName"
adb -d shell screenrecord /sdcard/$fileName || adb shell echo \04
# running extract in a sub-process means the next video doesn't have any time-gap from the last
wait; extract & continue
done
}
record && wait && exitScript
}
(screenDVR) && printf "\ncontinue main loop\n"; exit