Apple Compressor (4.1.2) User Manual
Page 40
Chapter 4
Advanced adjustments
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GOP structure: This property is available only when the “Frame rate” property is set manually
(does not use Automatic).
Note: Automatically determined properties, including the “Frame rate” property mentioned
above, are assigned by Compressor based on your source media file. Therefore, "Automatic”
properties are strongly recommended.
Compressor provides three methods of grouping frames, or “pictures,” in encoded video: as
I-frames (intra-frames), P-frames (predictive frames), and B-frames (bi-predictive frames). The
“GOP structure” pop-up menu includes several methods of combining frames:
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IP: Use IP only if your media contains fast motion that isn’t encoded with sufficient quality
using an IBBP or IBP structure.
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IBP: Use IBP only if your media contains fast motion that isn’t encoded with sufficient quality
using an IBBP structure.
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IBBP: Recommended for 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.
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GOP size: This property is available when the “Frame rate” property is set manually (does not
use Automatic).
Note: Automatically determined properties, including the “Frame rate” property mentioned
above, are assigned by Compressor based on your source media file. Therefore, "Automatic”
properties are strongly recommended.
This slider specifies how many frames are contained within a GOP (group of pictures). The
values available in the slider are 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).
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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).
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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.
Cropping and padding
Customize the final cropping, sizing, and aspect ratio using the Cropping & Padding properties.
Cropping removes video content from an image. Padding scales the image to a smaller size while
retaining the output image’s frame size. For more information about these properties, see
on page 67.
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Cropping: This pop-up menu sets the dimension of the output image. The custom option
allows you to enter your own image dimensions in the fields; other options use predetermined
sizes. The Letterbox Area of Source option detects image edges and automatically enters crop
values to match them. This is useful if you want to crop out the letterbox area (the black bars
above and below a widescreen image) of a source media file.
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Padding: This pop-up menu sets the scaling of the output image while retaining the output
image’s frame size. The custom option allows you to enter your own scaling dimensions in the
fields; other options use predetermined dimensions.
67% resize factor