MPEG II 的DAR：
Based on "aspect_ratio_information", stored in the Sequence Header
If aspect_ratio_information is "1", PAR = 1:1, and therefore DAR = SAR
If aspect_ratio_information is "2", "3", or "4", DAR = 4:3, 16:9 or 2.21:1 respectively,
in which case PAR = DAR/SAR
However (this is relatively rare):
If Sequence Display Extension is present and display_horizontal_size
and display_vertical_size are present and differ from the SAR,
then their ratio will replace SAR in the above equation.
DVD就这几种DAR，但两边要不要切8就看做DVD的人是啥心情了。
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至于做dvdrip，
个人认为，只要不是纯黑就不应该切, 反正PAR自己算就行了。
