This is OK information somewhere. But the following code gives you saved Audio/Video/ScreenRecord Composition, ready to play as is too:
set thePackagePath to POSIX path of (path to desktop) & "SomeMedia.qtpxcomposition"
tell application "QuickTime Player"
activate
stop document 1 -- to stop capture
delay 2
set thePackageFile to (thePackagePath as POSIX file)
save document 1 in thePackageFile
quit
end tell
And, I believe, that is Apple approach too.