Apple Final Cut Pro 5 - Manual (Page 1635)

284 Part IV Settings and Preferences
 Limit real-time video to N MB/s: Final Cut Pro uses this number to limit how many
video streams can play back from your scratch disk in real time. This is useful when
multiple editing systems are sharing the same media (such as a storage area
network, or SAN), or when you have a scratch disk with a limited data rate, such as a
PowerBook hard disk.
For example, suppose you try to play a sequence with six simultaneous video tracks
containing DV media, and Final Cut Pro warns you that frames were dropped during
playback. If you then try to play a sequence with five simultaneous video tracks and
no frames are dropped, you know that your scratch disk can handle no more than
five simultaneous DV video streams. Since DV has a data rate of 3.6 MB/sec., you can
select the “Limit real-time video to” option and enter 18 MB/sec. (5 x 3.6 MB/sec.) in
the number field. Now, if a sequence requires a sustained data rate of more than
18 MB/sec. for playback, Final Cut Pro shows a red render bar over this portion of the
sequence.
Note: Final Cut Pro always allows a single video stream to play, even if the data rate
limit you set is below the data rate of a single video stream. For example, if you set
the data rate limit to 1 MB/sec., Final Cut Pro would still play back a single DV video
stream, even though its data rate is 3.6 MB/sec.
More About Audio Playback Quality
Sample rate conversion occurs when you use clips with audio sample rates that differ
from the sample rate in your sequence’s settings. If the sample rate of your media
files matches the sample rate of the sequence, this pop-up menu has no effect.
Transitions between rendered and nonrendered portions of audio clips are also
affected by the quality chosen in the Audio Playback Quality pop-up menu. For
example, if you choose Low Quality and you play a partially rendered clip that
contains a reverb, then you won’t hear the tail of the reverb when the playhead
crosses the boundary from a rendered to nonrendered section of the Timeline.
However, if you choose Medium or High quality, you hear the reverb even when
crossing the render boundary.