Apple Compressor 3 User Manual download pdf (Page 167)

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

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Apple Compressor 3 User Manual Page 167