GOP Length
Longer GOP lengths produce more efficient encodes by reducing the number of I-frames
but are less desirable during short-duration effects such as quick fades and quick camera
pans.
• SD-Based DVDs: The maximum GOP length for SD projects is 18 frames for NTSC or
15 frames for PAL. The minimum GOP length depends on the GOP pattern. For example,
an IP pattern can have a length as short as two frames.
The integrated MPEG encoder uses a GOP length of 15 frames for NTSC and 12 frames
for PAL SD assets.
• HD-Based DVDs: Because HD projects can use both interlaced and progressive video
assets, they have different GOP length maximums.
• NTSC interlaced assets: 18 frames per GOP
• NTSC progressive assets: 36 frames per GOP
• PAL interlaced assets: 15 frames per GOP
• PAL progressive assets: 30 frames per GOP
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Chapter 4
Preparing Video Assets
Note: 24p assets have their GOP structure based on their display rate, not the encoded
rate. A 24p asset encoded to play in an NTSC project has a display rate of 29.97 interlaced
frames (with an 18 frames per GOP maximum) or 59.94 progressive frames (with a
36 frames per GOP maximum).
The integrated MPEG encoder uses a GOP length of 15 frames for NTSC and 12 frames
for PAL HD assets.