Currently Being ModeratedApr 10, 2013 11:12 PM (in response to djeightysix)
That does look odd. In an earlier version of iMovie I noticed something similar, but it appeared only between separate clips - not within the same clip. So I just trimmed off the frames causing the problem. From memory, I think it was the first frame of the incoming clip (but may have been the last frame of the outgoing clip). I haven't seen the problem in iMovie '11 - are you using this version?
In your example, the flash appears on one frame at a time only - at the 1:06 position and the 2:16 position (that's seconds:frames). The flash comprises 2 side by side squished versions of the main clip, appearing at the top of the clip. Here's a screenshot from your video:
Can you give us some information about the camera please (including the camera's recording format). I notice that you optimized the video upon import to iMovie, which converts the camera clips to Apple Intermediate Codec (AIC). That's a good thing as iMovie works best with that format.
Do you recall whether the camera footage played back OK in the camera, and perhaps when connected to a TV? I'm thinking that there may be an issue with your camera. But, having said that, my issue disappeared after an update to iMovie (can't remember which update fixed it though).
JohnMacBook Pro (15-inch Late 2008), OS X Mountain Lion (10.8.3), Sony HDR-SR7 & DCR-TRV20E