Matrox MXO2 PCIe Host Adapter - Manual (Page 270)

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Chapter 18, Using the Matrox Video for Windows Codecs
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Regular Sets the regular (default) zig zag scanning pattern of the AC
coefficient of the DCT block as defined in the ISO/IEC 13818-2
(figure 7-2) specification documentation.
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Alternate Sets an alternate zig zag scanning pattern of the AC
coefficient of the DCT block as defined in the ISO/IEC 13818-2 (figure
7-3) specification documentation. Use this setting when capturing or
rendering video at a high data rate (for example, at a data rate of 100
Mb/sec or higher).
6 Under Rounding Type , select one of the following:
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MPEG-2 Rounds the AC coefficients up to the nearest whole number
when calculating the quantization coefficient.
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Matrox Custom Truncates the AC coefficients to the lowest whole
number when calculating the quantization coefficient. In some cases, this
setting may yield less artifacts in graphics.
7 Select the Force Frame-based DCT setting to render macroblocks as
frames rather than as fields. In some cases, graphics will yield less artifacts if
this option is selected.
8 Click OK to save your settings. The settings you selected will be used each
time you render material with your program, until you change the settings
again.