Quicktime Pro 7
Effect of changing data rate

With a higher data rate we can have shaper frames and better sound. This short test of the sunrise, 7 seconds, shows how sometimes a much lower data rate is almost as good. This experiment is to see the difference in Broadband Low, Broadband Medium, or Broadband High. The default size is different for each choice, but I reset all to 320X240, the same size as the original movie file. Broadband Low, 10fps, Bitrate(Data rate) 80, file size 3 megs reduced to 77K. Broadband low sets the size to 160X120, so I had to go to Options, then Size, and change it back to 320X240. Click the play triangle to start. Broadband Medium, 15fps, file size 3 megs reduced to 195K. Yes, the file is over twice as big for only 50% more frames but the quality should be better as the bitrate is now 220. Size is 320X240 for Broadband Medium Broadband High, 30fps, file size 3 megs reduced to 564K. Yes, the file is over over seven times as big as the 10fps version, but the quality should be better as the bitrate is now 672. Broadband High sets the size to 480X360, so I had to go to Options, then Size, and change it back to 320X240.

So we are beginning to see that sometimes the bitrate has a much larger effect on file size than frames per second. Hmmmmm, this is beginning to get interesting. We can vary the file size just by changing the max Bitrate, with a corresponding change in quality. With a higher bitrate, we can have more fps or sharper pictures. Next: Editing a movie Quicktime Pro 7 index Page view counter