Can’t record screen on Yosemite with quickTime Player

How about this: It's not exactly what you want, but achieves roughly the same thing.

I seem to remember pre-OS X you could activate an app and keep it from being frontmost, but that appears not to be possible these days (or I imagined it.)

to replaceFrontQTPlayerWithFile(aFile)

tell application "QuickTime Player"
    activate

    try
        set frontDoc to front document
        close front document
    on error err number errNum
        if errNum is -1719 then
            -- There is no open document
        else if errNum is -10000 then
            -- Front doc exists, but does not really...
        else
            log err
        end if
    end try

    open aFile
    play front document

    -- Hide QTP
    tell application "System Events"
        keystroke "h" using command down
    end tell

end tell
end replaceFrontQTPlayerWithFile


on run
    set unixFile to "/Users/diggory/Music/iTunes/iTunes Music/Music/Underworld/Oblivion With Bells/01 Crocodile.m4a"
    set macFile to POSIX file unixFile
    set fileRef to (macFile as alias)
    my replaceFrontQTPlayerWithFile(fileRef)
end run

Finally figured it out - apparently the Movies folder in my home directory had a weird permission set on it and things couldn't be written to it, which caused QuickTime to give a very descriptive message "The operation could not be completed" and saving to a different folder (or after fixing the permissions on Movies), worked.