Apple Final Cut Pro 7 - Manual (Page 1767)

• Key Frames: Key frames are available if your selected codec uses temporal compression.
Most video frames in close proximity have a high percentage of visual redundancy.
Compression key frames reduce data rate by only storing complete images at regular
intervals or when abrupt visual shifts occur. The remaining frames only store information
about the change, or delta, between themselves and the key frame. Increasing the
number of frames between key frames increases the amount of compression and makes
the final file size smaller.
Key frame
Key frame
Delta frames
Depending on the codec you use, the movie file’s quality, especially for clips and
sequences with a lot of motion, may decrease if there are too few key frames specified.
If there’s a lot of motion in your media file, you need key frames more often than you
do with more static footage, such as an interview sequence. A setting of one key frame
every ten frames is a good starting point.
Some video codecs allow you to insert a key frame every certain number of frames,
while other video codecs use natural key frames by scanning the whole file to detect
where the major similarities and differences occur and inserting the key frames
accordingly.
• Automatic: QuickTime adds temporal compression key frames when necessary.
• Every N frames: Temporal compression key frames are created every N frames. Because
key frames require more data to store than the in-between frames, a higher value
here results in a movie with a lower data rate.
• All: A key frame is added on every frame. This increases the data rate of the movie
significantly.
Data Rate Area options
The Data Rate Area contains the following options:
• Automatic: The selected codec adjusts the data rate of your QuickTime video
automatically.
1767 Chapter 106 Exporting Using QuickTime Conversion