Ulead 1.0 - Manual (Page 83)

SpruceUp User’s Guide 4—11
MPEG-2
• Full D-1: 720x480 NTSC, 720x576 PAL
• Cropped D-1: 704x480 NTSC, 704x576 PAL (matches analog blanking)
• 1/2 D-1: 352x480 NTSC, 352x576 PAL
• SIF (Standard Interface Format): 352x240 NTSC, 352x288 PAL
Picture Frame Rate
SpruceUp supports NTSC (29.97fps) and PAL (25fps) frame rates. Be sure the video frame
rate matches the frame rate set for SpruceUp in the Preferences dialog.
Warning: You cannot mix NTSC and PAL MPEG assets in a project –
compile errors will result.
Aspect Ratio
DVD supports 4:3 (conventional TV) and 16:9 (widescreen) aspect ratios. 16:9 video is
anamorphic, meaning it is compressed horizontally (things look skinny). A flag setting on
the title triggers the end user’s player to expand the picture out to a real 16:9 aspect ratio.
SpruceUp supports 4:3 only, but will import 16:9 video and process it as if it was 4:3
(playback will be as 4:3, not 16:9).
Chroma Format
The DVD specification requires a 4:2:0 chroma format. There are several component
standards, most dealing with how many chroma samples there are for each luma sample. A
C
B
and C
R
sample is taken for every other luma sample on every other horizontal line. This
leads to 2:1 chroma downsampling both horizontally and vertically.
What’s a GOP?
A major function of MPEG encoding is to identify redundancy not only within a frame, but
also among a group of frames. A scene with no movement except a car driving by has a lot
of redundancy over time. In this case, a single complete frame could provide the majority of
the video; subsequent frames only need to provide for the areas that changed. MPEG uses
three frame types to define the video, with a GOP (Group Of Pictures) setting to define the
size of the group and its order.
An MPEG video stream is composed of Intra (I) frames, Bi-directional (B) frames, and
Predicted (P) frames. An I-frame, also known as a reference or “key” frame, contains the
complete image of the current frame, without reference to frames that precede or follow it.
P-Frames are encoded from a “predicted” picture based on preceding frames, and B-Frames
are encoded based on an interpolation from other frames that come before and after.
Therefore the I-frame is the only type of frame that can stand by itself, without requiring
information from other frames in the GOP. Every GOP contains one I-frame.
Chapter points in a DVD Movie can be entered only at GOP boundaries. Otherwise, the
picture could not be reproduced when the chapter point is accessed at random. Likewise,
MPEG editing functions such as the EyeFrame setting can be done only at GOP boundaries.
There are three aspects to choosing a GOP setting: Length of GOP, the GOP pattern, and
whether the GOP is “open” or “closed”.
GOP Length
Longer GOP lengths produce efficient encodes, but are less desirable during short duration
effects such as quick fades and quick camera pans. DVD defines the maximum lengths to be
18 frames for NTSC or 15 frames for PAL.