3

About the Frame Sync Setting
The Frame Sync setting defines an H.264 group of pictures (GOP). One difference between
MPEG-2 and H.264 encoding is that a frame within a GOP can reference frames other
than those that it is closest to, which means the decoder must store all potential reference
frames in order to be able to access them. The first frame of an H.264 GOP is a special
I-frame known as an instantaneous decoder refresh (IDR) frame that also flushes the
decoder’s reference frame buffers.
FS PS
GOP
Two seconds default
GOVU
0.5 seconds default
Partial Sync
key frame
PS PS
Frame Sync
key frame
This means that frames within the GOP defined by the Frame Sync setting can reference
any other frames in that GOP, but not those outside the GOP. The result is that a longer
frame sync setting creates a larger GOP, with more frames available for referencing, while
a shorter setting results in a smaller GOP and fewer frames that can be referenced.
Additional I-frames, referred to as partial sync key frames, are added to the GOP. These
standard I-frames define a group of video access unit (GOVU).
Important: To conform to the HD DVD specification and its requirements for maximum
GOVU length, Compressor inserts a partial sync key frame every 0.5 seconds.
Using Multi-Pass for DVD Authoring
To ensure that any H.264 files you create with Compressor will compile properly into HD
DVD-compliant files in DVD Studio Pro, make sure that multi-pass encoding is turned on.
To turn on H.264 multi-pass encoding
1 Open the Settings tab.
2 Select the setting in the Settings tab that you want to modify. (Or select a setting already
applied to a source media file in the Batch window.)
3 Open the H.264 Encoder pane in the Inspector window.
4 Select the Multi-pass checkbox.
About the Bit-Rate Settings
When determining average and maximum bit rates for DVD playback, remember to
consider the bit rate of your audio tracks as well as the H.264 bit rate.
167Chapter 13 Creating H.264 for DVD Studio Pro Output Files