When you record a movie using Screen Capture Video Software, you are actually saving a sequence of bitmaps (known as frames), that, when displayed in rapid succession, exhibit motion.
If more frames are recorded per second, the resultant animation will also be smoother. However, this will also cause the file size of the movie to be much larger.
In the process of recording, Screen Capture Video Software allows you to specify two video rates: the input rate and output rate. The input rate tells your computer how many frames to record per second. The output rate tells your computer how fast to play them back. Usually, these two rates are equal, so that the time of playback is equal to the time used in the recording.
However, these two rates can also be different. Normally, you do this only if you want to create a time-lapse movie. For example, you can capture a frame once every hour and play the frames back at 20 frames per second.
The default value is set at 20 frames per second for the output (playback) rate and 20 frames per second (corresponding to 50 milliseconds sleep time) for the input /capture rate.
There is also a third rate: known as the keyframe rate. When a frame is saved in an AVI file, they can either be saved as a full frame, or only as a difference to the previous frame. This keyframe rate specifies how often full frames are written to the AVI file. A high value means you can fast forward/rewind to a particular frame in your movie much faster. But it also means a higher file size.