In Quicktime Player 7, under Snow Leopard with Perian, if you open the A/V controls (cmd-K), it has a playback speed slider which you can set from 0.5 to 3.
I like playing videos faster to save time. I noticed that if you play the same video on double speed in Quicktime 7 and in VLC, the audio sounds faster and harder to follow in VLC. At first I thought Quicktime was doing a better job speeding up the sound.
But then I timed it with the stopwatch on my iPod touch.
VLC and the new Quicktime Player (version 10.0 in the about window) both play one minute of video in 30 seconds on my stopwatch. They correctly play at double speed.
But with quicktime 7:
When the slider is set to 1.5 playback speed, it goes at 1.25 speed.
When the slider is set to 2 playback speed, it goes at 1.5 speed.
When the slider is set to 2.5 playback speed, it goes at 2 speed.
When the slider is set to 3 playback speed, it goes at the full 3 speed.
At .5, .75, and 1 speed on the slider, it plays at the correct speed.
Isn't that bizarre? And disturbing. It lied to me! And the slider doesn't even have a linear effect on playback speed.