Why does iMovie project jerk and stop and start in preview?

11-30  Source: Network gathering  Views:0 

I have been making iMovies with iMovieHD for years using photos with the Ken Burns effect.
Recently after a movie project gets more than a few minutes long with typical audio and transitions, I no longer can preview it without it jerking and stopping and starting.
Obviously this does not allow me to see what I am doing, how the music matches or doesn't match my photos.
I have tried emptying the iMovie trash and emptying my finder trash, no change.
I have made sure there is plenty of hard disk space on my internal drive, where iMovie and the movie file is located.
Any ideas?
a. Emptying the trash - something I alway avoid - no matter why.
b. Plenty of free space on internal (start-up) hard disk ? > 25Gb after
project is captured and edited ?
c. Deleted iMovie pref file ?
d. Known trouble maker: Lot's of audio clips. eg > 50 gives a stuttering result
Mix down audio to one audio clip.
e. What kind of original material. 12-bit audio or recording in LP-mode (90min
on a 60min tape) GIVES problems + audio sync troubles.
f. .mpg4, .avi, .wmv and other ailient file formats also is problematic.
g. movie stored on an external USB/USB2 hard disk - often troublemaker.
I use FireWire AND ONLY: Mac OS Extended formatted -
Yours Bengt W
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