Apple DVD Studio Pro 4 - Manual (Page 77)

When adding markers to a track in DVD Studio Pro, you can only place them at GOP
boundaries. This means that you will often not be able to place them exactly where you
want them. When you place the markers with a video editor, the integrated MPEG encoder
automatically forces an I-frame at that position, placing a GOP boundary exactly at every
marker and providing perfect marker placement. Markers placed in Compressor before
it is used to encode the video are also perfectly placed.
Using Compression Markers to Improve the MPEG Encode
MPEG encoding is based on the placement of I-frames, P-frames, and B-frames within a
GOP (see
Working with GOP Settings ). The I-frames encode a complete frame, while the
P-frames and B-frames only encode the parts of the video that change between the
I-frames. When there is a sudden change in the video content on a P-frame or B-frame,
such as a cut to a new scene, the output of the MPEG encoder can have significant artifacts
until it reaches the next I-frame.
The integrated MPEG encoder uses compression markers to force an I-frame into the
encode at a specific frame, modifying the surrounding GOP structure to keep the encode
DVD-compliant.
Adding compression markers at places in the video where sudden transitions occur can
produce better MPEG encodes when you use the integrated MPEG encoder. You can
manually place compression markers in Final Cut Pro and Final Cut Express. As with chapter
markers, an I-frame is forced at their position. The difference is that compression markers
do not import into DVD Studio Pro as chapter markers and do not count against the 99
chapter marker limit for a track.
Note: Final Cut Pro automatically adds compression markers at each edit point. These
are not processed when encoding the video with the integrated MPEG encoder. Only
compression markers you manually add in Final Cut Pro are processed. See
Using
Final Cut Pro and Compressor for information on these markers and Compressor.
About the Markers You Add in an External Editor
There are several issues to be aware of when adding chapter and compression markers
in an external video editor:
• DVD tracks can support a maximum of 99 chapter markers. Because compression
markers are only used in the MPEG encoding process, they do not count as chapter
markers and do not count against the 99-marker limit. Because you can add several
video assets to a single track in DVD Studio Pro, you must keep in mind that the
99-marker limit applies to the total markers of all assets on the track.
• You cannot place markers closer than one second to each other or within one second
of the clip’s start or end in the editor. This gives the encoder the flexibility to modify
the GOP structures in that area to accommodate the added I-frame.
77 Chapter 4 Preparing Video Assets