Simultaneous synchonised launch

General Linux Question
1

OK - so with my IP security cameras, they kept getting out of sync when launched via MPV and RTSP stream…

I wanted a shell script or some solution to launch BOTH at the EXACT same time… I don’t think cron would good for that (for a start - I’ve NEVER tried launching a GUI application from cron)…

Went hunting for solutions - they looked way too complex for something that should be simple… Gave up :

───────┬───────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────
       │ File: /home/x/bin/twincam88.bash
───────┼───────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────
   1   │ #!/usr/bin/env bash
   2   │ # fire up MPV @ VGA on BOTH TP-Link webcams
   3   │ SCRIPT=~/bin/wholycows.bash
   4   │ loopy_cnt () {
   5   │ for CAM in "1 2"
   6   │ do
   7   │     $SCRIPT $CAM 2 > /dev/null 2>&1 & disown
   8   │ done
   9   │ }
  10   │ $SCRIPT 1 2 > /dev/null 2>&1 & disown
  11   │ $SCRIPT 2 2 > /dev/null 2>&1 & disown
───────┴───────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────

I don’t use that loop “loopy_cnt” - but I left it there in case I decide to try that method…
I just wish I could do BOTH those last two lines AT THE SAME TIME, instead of in that sequence, even if it less than 1 second delay…
But it kinda works…

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2

The only way to do that in a serial computer is to make them one process.
Multitasking is a sham, it makes it look like 2 things are happening at once, but it is really sharing time slices.

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3

@daniel.m.tripp Did you take a look at GNU Parallel?

GNU Parallel is a powerful tool that allows you to run commands in parallel, providing flexibility and control over the execution process.

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4

I’d read about this a few years ago - interestingly - it didn’t come up in any google searches (maybe I should start using duck duck go)… Just installed it…

Could be the answer…

5

Parallel is not quite simultaneous, but it may be close.

6

Very close, if each job is running in separate cores.

7

OK - tried parallel - doesn’t seem much different from running two commands in a bash script…

And it launches the MPV sessions on my main display - not the display I’m running that terminal session in. With my shell script, it fires up the MPV windows on the same screen as the terminal session…

So - I think I’ll just use my shell script… if the cameras get several seconds out of sync, I’ll just kill the feed and run my shell script again…

Now I just gotta read up on launch options (geometry) for MPV i.e. which screen, co-ordinates and dimensions of each MPV window…

–geometry=1280x720 works fine…

Now I need some logic to decide the X/Y position of each window, so that the first camera is at 0,0, and second camera is at 1281,0

So - result :

╭─x@titan ~/bin  ‹main*› 
╰─➤  bat twincam96.bash 
───────┬────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────
       │ File: twincam96.bash
───────┼────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────
   1   │ #!/usr/bin/env bash
   2   │ # fire up MPV @ VGA on BOTH TP-Link webcams
   3   │ UZER="REDACTED"
   4   │ PSWD="REDACTED"
   5   │ CAM1=REDACTED
   6   │ CAM2=REDACTED
   7   │ STREAM=stream2
   8   │ # SCRIPT=~/bin/wholycows.bash
   9   │ # /usr/bin/mpv --geometry=1280x720 rtsp://$UZER:$PSWD@$CAM:554/live/$STREAM &
  10   │ # $SCRIPT 1 2 > /dev/null 2>&1 & disown
  11   │ # $SCRIPT 2 2 > /dev/null 2>&1 & disown
  12   │ /usr/bin/mpv --screen=1 --geometry=1280x720+0+0 rtsp://$UZER:$PSWD@$CAM1:554/live/$STREAM > /dev/null 2>&1 & disown
  13   │ /usr/bin/mpv --screen=1 --geometry=1280x720+1281+0 rtsp://$UZER:$PSWD@$CAM2:554/live/$STREAM > /dev/null 2>&1 & disown
  14   │ # /usr/bin/mpv --screen=1 --geometry=1280x720+1+1 rtsp://$UZER:$PSWD@$CAM1:554/live/$STREAM &
  15   │ # /usr/bin/mpv --screen=1 --geometry=1280x720+1281+1 rtsp://$UZER:$PSWD@$CAM2:554/live/$STREAM & 
───────┴────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────

And no matter what screen the terminal is running on from which I run the shell script - they go to screen 1 (default/main is “0”)

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