Quote What's the reference for this? There's no warning that you're attempting to do something problematic. No graying-out of interpolation, or even simply not applying that option if it was previously selected but now you're trying to use it on a 9:16 clip, PD happily accepts the request then dives into oblivion

optodata, like most things, does a reference exist for:
1) Variable bitrate MP3 files not working properly
2) Highly variable fps video not working properly
3) Highly variable bitrate video not working properly
4) Hardware decoding not working properly
5) Hardware encoding not working properly
6) Timeline preview render not working properly

Just to name a few, I think you get the point, the reference you ask of is like most PD things, just user experience, that’s all. After all, is not the stated forum objective to “Share your knowledge and experiences of video editing with PowerDirector 21“. If you want a reference on what interpolation technique PD uses and what exact video’s are supported, contacting CL for an answer would be suggested, good luck with an appropriate answer! In the meantime, it’s just users sharing what they have observed, I’ve never seen 9:16 interpolation work for me yet, hence the statement. The workaround I provided has worked for me at times. Always welcome being proved wrong though, everyone gains.

Jeff

It wasn't an accusation. I simply asked for a reference for your declaration as I didn't remember any limitations on interpolation regarding AR.

If you'd said anything like "I don't think" or "I haven't seen" PD work like that, it would've been clear you were speaking from personal experience.