The problem isn't that control is not being returned to your script, it's that the output from the echo command isn't being captured and reported to you. It could be that Alfred is closing the transient Terminal.app window that it's using to run the script. To test that add a sleep 60m to the end of the script which should keep the window on the screen.

Or it could be that all stdout/stderr from the script is going to /dev/null or something similar. Make sure Alfred isn't throwing away the output. Based on our comment conversation it sounds like that's what Alfred does with std I/O.

Don't know any applications that do what you're after but here's a couple of alternative options for you. Second two won't pause the video but will give you instant capture.

1. Pause the video then capture at will? Sorry if that sounds too obvious! Guess that you might be viewing live footage so that might not work...
2. Shift+command+4 will give you a regional marquee grab (takes grab on mouse-up) saved to the desktop (or add the control key to add to the paste buffer).

3. Use Grab - its the OSX 10.6 native screen capture app under /applications/utilities. It has the option to grab the current window (or selected region or entire screen).

   1. Choose the option you want
   2. Make the screen ready (ie video playing)
   3. Choose it with a click You may be able to set this up as a keyboard shortcut under /system preferences/keyboard/keyboard shortcuts - I've not tried.

I hope that helps!