Wow, it must be "digital video day" 'cause this is the second one I've seen on such a topic.
Wall$treet's actually mistaken on this topic (a rarity, you'll note). If the video can be stepped through, frame by frame, and not be missing pieces not seen when it's "going too fast", then the playback application is spewin' it out too fast.
Why?
This can occur when there's background tasks or when the data is too big at that portion of the video. An analogy would be too much water for too small a hose. Picture the cartoon of a swollen water hose, and how it bursts forth really quickly after some delay. Digitally, that's what *can* occur wit' digital video.
The solution? More memory to the player can help. Failin' there, you need a faster processor and/or some sort of faster I/O (a faster drive card and a faster drive, for a Windows example).
Now, when it plays better the second time, the problem's bein' assuaged by "queuing", where the application is queuing the video into memory. It works wit' shorter clips, and is helped when the application hogs all the memory it can get. Means that you wanna fully QUIT that app, too, so you don't start getting memory errors.
Why don't I blame the clip? 'Cause "it plays fine on my config." It's that most hated of answers, when given without solutions.
g'luck!