Quicktime Pro 7
Effect of changing data rate

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With a higher data rate we can have shaper frames and better sound. I'm replacing the original movie I used on this page with one of Sonny that has more motion in it. That short test of the sunrise, 7 seconds, just didn't show much difference with changing the frames per second because there wasn't much motion. This 14 second movie of Sonny walking and flipping his tail is better. 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 6.9 megs reduced to 176K. Broadband low sets the size to 160X120, so I had to go to Options, then Size, and change it back to 320X240. The sound quality is poor with the default Broadband Low settings, so I changed this one to stereo so I could increase the bitrate.

Click the play triangle to start.

Broadband Medium, 15fps, file size 6.9 megs reduced to 252K. Yes, the file is bigger for 50% more frames but the quality is better as the data rate is now set to 120. Sonny moves more smoothly with more frames per second. Size is 320X240 for Broadband Medium

Broadband High, 30fps, file size 6.9 megs reduced to 496K. Yes, the file is over over twice as big as the 10fps version, but the quality should be better as the bitrate is now 240. While the default data rate is 672 for Broadband High, I lowered it to correspond only with the frame per second rate to keep from having an even larger file size. 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. So many options it is easy to get confused and forget what changes I made, it helps to write everything down.

Next: Editing a movie

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