I have an AppleScript that uses ffmpeg to process some files. Each single file process takes a while to complete. During this time I often need to run other AppleScripts that use the shell and ffmpeg but these scripts hang, waiting for the other script to complete the shell command.
Is there a way to open a separate instance of the shell per AppleScript so one does not interfere with the other and can run simultaneously?
I think using the do script command of the Terminal application it can be done. But as a person who also often has to code films, I can say that this makes little sense. The encoding speed is simply divided by the number of processes. Better, close all unneeded applications and processes to increase the speed.
tell application "Terminal"
do script "ffmpeg ...." -- one instance
do script "ffmpeg ...." -- second instance
end tell
Thanks @KniazidisR for the tip! No ideal to my use case since I collect data back from the shell command, I would have to figure out that part now using the terminal application.
So there is no way of doing these without opening Terminal?
BTW I’m not talking about processing more than one file to save time. Is more like SCRIPT#1 is running for hours at a time (takes about 30 minutes per file) and then I need to do a quick run of a different SCRIPT#2 that normally takes less than 10 seconds per file but I can’t, it hangs waiting for SCRIPT#1 to finish with its current file.
Why so?
Create 2 scripts with one do shell script "ffmpeg …" in each, save them as 2 separate applications with unique names, and run them anytime, anywhere. Moreover, you will have complete control over them.
It is also possible (2 ways) to create instances of one single application located on the disk, but you will not have control over the instances (processes). So it won’t work for you.
So I created two very simple test script to try things out because I ended up waiting looong time to figure out the fix wasn’t working on my original scripts :lol: I hope I’m doing this test right, bear with me here:
S1:
set dResult to do shell script "sleep 5"
S2:
set dResult to do shell script "echo test"
display dialog "DONE!"
When I run (via AppleScript app) S1 and then S2 right after. S2 hangs for 5 seconds and then displays “DONE!” as expected (the issue in question)
However, if I save both S1 and S2 as independent apps, and run them from Finder, S1 then S2, the “DONE!” dialog is displayed immediately, before S1 finishes. So yeah @KniazidisR is absolutely right and this is an even better alternative to calling the terminal app. Thanks! 
However, I would really like to figure out a way of doing this from AppleScript since I rarely save my scripts as apps (I’m always tweaking the scripts, calling scripts within scripts, calling scripts from other apps like LaunchControl, etc. I would have to change my workflow a bit :))
@Fredrik71, I’m trying to understand your approach. I’m not an expert in bash scripting and using variables in it but I think I understand your code and don’t see how it can help the issue in question. I changed S1 to the following:
S1:
set dResult to do shell script "#!/bin/bash
sleep 5"
and still, S2 hangs for5 seconds.
Can you please advise?
Yes, I would like to get data back from the shell command but I’m trying to solve the multiple shell instances issue first since you already gave me two great options for getting data back via pbcopy and log, and I might not even have to use them if I get the main issue resolved.
As I explained before, by saving the scripts as individual APPs and running them from Finder, both apps get their separate shell instance, allowing for concurrent operations. However, running the same scripts simultaneously from AppleScript (from their separate AppleScript windows) will cause one to wait for the other. It is as though only one shell instance is assigned to AppleScript.
Is there a way to invoke a separate instance from within AppleScript without having to use the terminal app?
I don’t see a technical reason as to why this shouldn’t be possible.
Sorry if you find inconsistencies in my posts, English is not my first language 
You have to save at least 1st script (S1) as app to solve your issue inside single script. Because AppleScript runs instructions one by one. It can’t run multiple threads the same time other way than using ignoring application responses block:
for example:
ignoring application responses
tell application "Delay5secondsApp" to activate -- use here 1st ffmpeg as app
end ignoring
tell me to display dialog "DONE!" -- use here 2nd ffmpeg as script: do shell script "ffmpeg..."