I tried 2 different SM versions: 3.9.8 and current 4.0.10 on 3 different Win 7 machines. Neither of these show hands video, even on from-the-box projects (Chasse-Neige), with assigned sample video from folder \SeeMusic\SeeMusic_Data\StreamingAssets\sample video\ . Creating new save file, piece, and manual assigning also doesn't show video. Repositioning video and similar actions don't work either.
What's wrong, or what I'm doing wrong?
SeeMusic is not compatible with Windows 7.
Windows 7 has reached end of life, and is no longer supported by the developers of the frameworks used by SeeMusic.
Upgrading to Windows 8.1 or Windows 10 should fix this issue.