Are you trying to play HD files off the Laptop OS drive? This is not recommended as you will have less then desirable results.
You can run fast ext. drives hooked up to a laptop.
If you do not have to print to tape then an occasional stutter won’t matter as you will probably compress the finished vid to DVD or Web.
But, you’re better off editing in HD. If you don’t want to then, run all the clips through compressor and make SD Widescreen ProRes or 8 bit uncompressed clips
Chris Tompkins
Video Atlanta LLC