When Apple replaced its aging QuickTime Player 7 with the newer QuickTime X, it touted the change as a ground-up rebuild to supplant the band-aided framework that had kept QuickTime 7 going for so many years. QuickTime may now be better poised to handle future media types and implementations, but since its announcement QuickTime X has not really done much, and has left many without obvious approaches for some of the basic controls that have been conveniences over the years.
One of these is the ability to play movie content at different rates than the default. If you have a high-framerate film, such as one that was shot at 60 or 120 frames per second, then playing it through QuickTime X it may default to 30 frames per second, having it run at 1/2 or 1/4 of the normal speed. To overcome this, you can still adjust the playback speed of your movie, though depending on the direction and precision you want, you may need to use script-based approaches for this solution.
Unfortunately Apple’s controls do not give you any way to specify a range at less than 1x, so if you want to slow your movie down you have to use an AppleScript-based approach, which can be done either in the Script Editor or in the Terminal. The script line that will do this for the foremost QuickTime document is the following:
tell application "QuickTime Player" to set rate of document 1 to 0.5
In this command, the 0.5 value will play the movie at half-rate, though you can specify any value. Negative values will run in reverse, and positive ones will run forward.
Since this is a one-line script, you can easily run it from the Terminal as well, since AppleScript lines can be interpreted using the “osascript” command (note even though it may wrap here, all of this is on one line):
osascript -e 'tell application "QuickTime Player" to set rate of document 1 to 0.5'
Unfortunately this means you will need to use another program (Script Editor, or the Terminal, or perhaps Automator or even a compiled AppleScript Application using this code) to control your movie playback speed in QuickTime X, but technically it is doable.
That being said, this ability is present in other media players as it was in QuickTime 7, where you can use hotkeys or a slider control to set the playback speed natively. Therefore, while you can use the above approaches, if you truly need to manage playback speeds then either download Apple’s older QuickTime 7 player, or use a third-party option like VLC.