Why does AVS require mod2 width for YV12 and YUY2?

[thewebchat]

Every description of the YV12/YUY2 formats I read suggests that mod2 width is legal in both progressive and interlaced mode, so why does AviSynth impose a mod4 limitation?

[Gavino]

This limitation only applies to the final output of Avisynth via the VfW interface, and is a VfW limitation.

[thewebchat]

Does this mean that there is a way in which I could do, say, "Crop(2,0,0,0)" or "AddBorders(1,0,1,0)"? What program will I need to read these scripts? I test all my AVS scripts with VirtualDub.

[Gavino]

This script works OK in AvsP

BlankClip(pixel_type="YV12")
AddBorders(1,0,1,0)

and you can step through the video frame-by-frame.
But when you then click on the arrow to play in an external player, the player gives the error that it has to be mod4.
Some programs use Avisynth directly (as a library) like AvsP, while others use the VfW interface (MPC, WMP). I suspect that most programs that deal generally with AVIs will use VfW, while those specifically designed to use Avisynth will use the library approach.

[jase99]

why does AviSynth impose a mod4 limitation?It doesn't. mod2 width works perfectly when AviSynth is accessed through the Avisynth.h API (e.g., avs2yuv). However, the AVIFile API imposes mod4. More info here: http://forum.doom9.org/showthread.php?t=143991#12