Shell Programming and Scripting

Hi everyone, thanks in advance for your kind help!

Here is what i need to achieve (simplificated example of course):

1-i have a "300-hour-music.mp3" file in my server HD side
2-a page HTML/PHP gets user input : the length of the track he want to listen, let's say 2 hours
3-a BASH script take the "300-hour-music.mp3" file and make a custom "custom.mp3" 2h music file (the BASH script may require 2-10 minutes to run fully...)
4-a page HTML/PHP gets the result "custom.mp3" and send it through a WEB stream player plugin


i have the "300-hour-music.mp3", BASH script, few ideas for user input gathering


I'm a bit skilled in linux scripting, I'm 100% new to PHP coding, WEB interfacing, etc...


How do i get php code to make something like this happen on the server HD:

====================================================
DIR=/server-static-home/music/temp/$RANDOM/
mkdir $DIR
cd $DIR

execute "../../bin/BASH-script-PART1.sh 2h " & // in background
# the BASH-script-part1.sh is killed after 30s --> php.ini timeout and i cannot change it!
# BUT the script started the sub processes ./sox still running on the server, which is goood!!

#check processes completion & wait : can take up to 5-10min !!!
while ("ps -ef | grep sox | grep combine | grep -v grep" != "") do sleep 5s / refresh page ?;


# now file "$DIR/custom.mp3" should exist

execute plugin WEB-player $DIR/custom.mp3

====================================================

Q : should i build a self-refreshing page with PHP ? because if i loop sleep command for > 1min the browser thinks connection out!

Q : do i have it all wrong ? is PHP the correct WEB inferface for what i need to do ?
--> any suggestion like use html, perl, asp ?

launch command exec("script") // the browser will wait until script completion
launch("start-web-player file.mp3") // all done!! easy