So from the planar/packed discussion, it seems that:
Packed is only needed for output. Otherwise it's easier (shared code with planar YUV) and faster (non-ancient CPUs only?) to process. Therefore IMO planar should be the default RGB format with ConvertToRGB24 etc, and Avisynth should only convert to packed before outputting (can it detect if whatever's at the other end wants packed or if it supports planar?). There should also be a "packed"-named bool argument when converting to any RGB format, in case an old filter requires it. What do you think?
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