Is this deinterlace avisynth script wrong?

[brassplyer]

Saw this in a collection of scripts. Shouldn't the Selecteven() be after the QTGMC command?

SetMTMode(3, 4)
FFMpegSource2("Z:\sourcefile.avi")
AssumeBFF()
Selecteven()
ConverttoYv12(interlaced=true)
SetMtMode(2) # uses less memory than mode 3
QTGMC (Preset="medium")
crop (8,0,-8,-8)

[jagabo]

It's probably wrong. But it depends on the source. For example, if someone created a 60 fps video by duplicating every frame of an interlaced 30 fps video SelectEven() before QTGMC() would be appropriate.

[ndjamena]

ConverttoYv12(interlaced=true)

May indicate the source file was progressive. Mayhaps an attempt to clean up a badly double-rate de-interlaced encode. Without seeing the file it was intended for and without understanding the abilities of the author we can only guess.

But for your purposes, I'm guessing it's wrong.

[jagabo]

ffmpeg source sometimes returns duplicate frames from interlaced sources -- each interlaced frame is returned twice in a row.

[ndjamena]

Known issues
•Interlaced H.264 is decoded in an odd way; each field gets its own full-height frame and the fieldrate is reported as the framerate, and furthermore one of the fields (odd or even) may "jump around". To get the correct behavior, you can try setting fpsnum and fpsden so that the framerate is halved (may or may not work). This issue is caused by libavcodec.