4.5

55Compressor User Guide
• Motion estimation: This pop-up menu sets the amount of motion processing that will be
performed on the file. There are three options:
• Good: The fastest processing setting. Use this setting when there is relatively low
motion between frames. In general, use Good with the one-pass encoding modes.
• Better: Provides very good results even in the presence of complex interlaced
motion. In general, use Better with Single Pass VBR (Best) and Two Pass VBR (Best).
• Best: The slowest processing setting. Use for the most complex motion and for
interlaced source files. In general, use the Best mode to maximize quality when
using Single Pass VBR (Best) or Two Pass VBR (Best).
• GOP structure: This property is available only when the “Frame rate” property is set
manually (does not use Automatic).
Compressor provides three methods of grouping frames, or “pictures,” in encoded
video: as I-frames (intra-frames), P-frames (predictive frames), and B-frames
(bidirectional predictive frames). These are collectively called a group of pictures (GOP).
The “GOP structure” pop-up menu includes several methods of arranging frames:
• IP: Use IP only if your media contains fast motion that isn’t encoded with sufficient
quality using an IBBP or IBP structure.
• IBP: Use IBP only if your media contains fast motion that isn’t encoded with
sufficient quality using an IBBP structure.
• IBBP: Recommended for the majority of MPEG-2 encoding situations.
Note: For most MPEG-2 encoding situations intended for use on a DVD, choose IBBP as
the GOP structure setting, and a GOP size of 15 for NTSC, or 12 for PAL.
• GOP size: This property is available when the “Frame rate” property is set manually
(does not use Automatic).
This slider specifies how many frames are contained within a GOP (group of pictures).
The values available in the slider are determined by the GOP structure property
(described above). The maximum GOP size you can choose within Compressor is 15
frames (NTSC) or 12 frames (PAL and 720p). The minimum GOP size for all video
formats is 6 frames (closed GOP) or 7 frames (open GOP).
• Automatically select bit rate: Select this checkbox to have Compressor automatically
compute the best bit rate for the output file, based on the duration of the source file.
To manually adjust the bit rate, deselect the checkbox and drag the “Average bit rate”
and “Maximum bit rate” sliders (or enter values in the adjacent fields).
• YUV 422 color encoding: This property appears in most built-in settings that output
MPEG-2 files. Select this checkbox to use YUV 422 color encoding for superior
chroma quality.