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How can i resize a video to 480 pixels high in AviSynth, while maintaining aspect ratio? Assume, for simplicity sake, the Bilinear resize.

i've tried:

source = DirectShowSource("TheClip.avi")
resized = BilinearResize(source, target_height=480)
return resized

But that gives the error

Script error: Invalid arguments to function "BilinearResize"

Note: The reason i don't supply a width is that i don't know a width. The script is being used by a media server, that now forces the use of AviSynth in order to perform resizing. i don't know the size of any video that anyone might choose to play - but i do know i need it resized to x480.

i presume AviSynth can do something like:

resized=BilinearResize(source, source.width*480/source.height, 480)

but that also fails:

Resize: YUY2 destination width must be even

i could keep going, trying to find a way to AddBorders or Crop, to make the width mod4, mod8, or mod16. Or i could ask here and maybe there already is a way to perform aspect-preserving scaling.

share|improve this question
Is there a way to cast ( source.width*480/source.height) to an int or something? – soandos Aug 28 '11 at 18:08
i'm pretty sure the problem is that the width it's calculating is something like 691x480. This conflicts with YUY2 which stores one color value for each pair of pixels; and this video is one pair short (should be 690x480 or 691x480) – Ian Boyd Aug 28 '11 at 19:23
So is there a round function? – soandos Aug 28 '11 at 22:55
up vote 3 down vote accepted

I'm a bit rusty with avisynth scripting, but I think this should work to get the width, based in a target height of 480, and a given modulo value... I couldn't test it as I don't have avisynth installed ...

 srceH = source.height
 srceW = source.width
    AR = (float(srceW) / float(srceH))
 targH = 480
 targW = int(float(targH) * AR)
 coMod = 4   # The codec modulo requirement 
 targW = ((targW / coMod) * coMod)
share|improve this answer
you missed setting the aspect variable. but after that it works great, thanks – yoshco Feb 12 '12 at 2:39
Thanks yoshco... Yes, I had AR in one place and aspect in another... Changed to AR. – Peter.O Feb 13 '12 at 11:01

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