Apple Final Cut Pro 5 - Manual (Page 1569)

218 Part III Output
Audio for DVD
Each DVD track can have up to eight audio streams. Each audio stream is independent
of the others—only one can play at a time. Each stream can have from one to seven
channels (as with 6.1 surround sound). Having multiple audio streams allows you to
include alternative language versions of the program, as well as special features such as
a spoken commentary.
Important: Do not confuse the way audio tracks in a Final Cut Pro sequence work with
how audio streams in a DVD Studio Pro track work. A DVD player cannot mix multiple
streams together. If you want to have music playing underneath the dialogue, you
must mix the two in the audio exported from Final Cut Pro so that one audio stream
contains both the music and the dialog.
About the MPEG Format
MPEG-2 is an internationally accepted compression standard developed by the Motion
Picture Experts Group (MPEG). MPEG-2 allows you to create broadcast-quality video
files and was designed to support high-resolution, high bit-rate video. It is the video
compression format used for high-quality video titles on DVD and home satellite dish
systems. All DVD players contain the hardware required for MPEG-2 playback.
MPEG encoding is based on eliminating redundant video information, not only within
a frame, but over a period of time. In a shot where there is little motion, such as an
interview, most of the video content does not change from frame to frame, and MPEG
encoding can compress the video by a huge amount, with little or no perceptible
quality loss. In shots with lots of action or a moving camera, MPEG encoding will not
be able to compress the video as much without sacrificing quality. Choosing encoder
settings that provide acceptable results at each extreme can be challenging.
MPEG encoders create I-frames, also known as keyframes or reference frames, that
store complete image frames. In between these frames are P- and B-frames that only
store information relating to what has changed since the last I-frame. In most cases,
the encoder adds an I-frame every half-second. Any sudden transitions that occur
between the I-frames can lead to encoding artifacts in the video. See “
More About
Compression Markers ” on page 221 for information on adding I-frames to reduce
these artifacts.