Can't scale a 1920x1080 movie to 640x360??

Question

Not only does quicktime sometimes stop playing videos, now it won't scale a HD video down to 640x360. It just comes out black. I can scale to 960x540 no problem... How strange.

Answer 1

It's a prores 422 HQ file, trying to convert to a h264. The question is, why does the video come out black?
Not sure why. Believe I have read that some users have had problems with ProRes 422 HQ when layering/compositing with certain other track data (e.g., PICT with alpha)—not something I have personally tried. Moreover, it doesn't explain why the problem would only appear at one specific target resolution. (I.e., does the same thing happen if you export to a 960x540 and then re-export using QT X or QT 7 Pro or export using an anamorphic strategy?)
Still have no idea what system OS or app (FCP 6, 7, X, QT X, QT 7 Pro, Compressor, etc.) or if you are using an export preset or custom settings. For instance, what is the actual H.264 video data rate for finished 640x360 file? That is, is it excessively low as if exporting only the "black background" or does the data rate look normal as if the video data was normally encoded but not being played back properly?