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AssumeTFF(clip clip)
AssumeBFF(clip clip)
Introduced in v2.0.4.
AviSynth keeps track of whether a given clip is field-based or frame-based. If the clip is field-based it also keeps track of the parity of each field (that is, whether it's the top or the bottom field of a frame). If the clip is frame-based it keeps track of the dominant field in each frame (that is, which field in the frame comes first when they're separated).
However, this information isn't necessarily correct, because field information usually isn't stored in video files and AviSynth's source filters just normally default to assuming bottom field first (with the exception of the MPEG2Source plugin which gets it right!). AssumeTFF and AssumeBFF let you explicity tell AviSynth what you believe the field order type a clip is.
AssumeTFF and AssumeBFF do not change the actual field order, just the internal state flags in AviSynth relating to the source clip used.
Examples:
AviSource("test.avi")
AssumeTFF
SeparateFields
will always return the top field of the first frame followed by the bottom field of the first frame and so on.
AviSource("test.avi")
AssumeBFF
SeparateFields
will always return the bottom field of the first frame followed by the top field of the first frame and so on.
