QuickTimePlayer is slow

my quicktime video player is very slow , usually a stuttering picture.

The normal logic flow hefre would be to determine the nature of the issue and then fix it. For instance,

1. If the movie data rate is excessively high for the for the codecs involved, then re-export it to a lower data rate.
2. If another app is not responding and is causing a data flow bottleneck, then close that app and fix it as a separate issue later.
3. If too many apps, threads, or other operations are active, close or cancel any that are not currently needed.
4. Check current RAM and disk cacheing operations to see if they are causing a slowdown.
5. Verify media status and/or fix file permissions if needed.
6. If the system has not been turned off in several days, you might want to reboot the system to allow certain "clean-up" operations to take place.

In short, there are a number of relatively normal things that can contribute to a system slowdown and it is usually wise to see what apps, events and activities may be monopolizing your system's CPU power..