The compressor will also automatically insert a keyframe whenever the scene changes so much that the interframe would be almost as big as a keyframe. If you need to quickly jump to any arbitrary point in the movie, a keyframe every 30 frames is about right. But using this interval can easily triple the file size or more. Once the Media Key feature is turned on in the Sorenson Video advanced features dialog, it stays on until you turn it off. To turn off the Media Key feature, go to the advanced features dialog and deselect the Media Key option, then recompress your video.
Tight control works well at higher data rates.
However, at low data rates the quick response of the data rate control mechanism may leave high motion areas with undesirable artifacts. The Data Rate Tracking slider allows the user to control how strictly the data rate is maintained. Relaxing the restriction can allow the encoder to give more data to short bursts of motion thus improving the overall quality of the video at low data rates. Smooth video playback is certainly possible at 640x480 with Sorenson Video and QuickTime. However, 640x480 playback is machine dependent and currently requires a fast computer.