@Mosu
Thanks again for your passionate work
It's unfortunate that FLAC support is limited; one doesn't have this problem if WavPack is used instead?
[Btw I don't think you need to bad-mouth (?) DVD just because it's not the newest format; there are some hidden gems - old shows - only available as DVDs, and in some cases BD versions may even look worse when the show was originally created as SD but forcefully up-scaled to HD w/o careful remastering...]
@hubblec4
On Windows, Unicode (non "ANSI") file names often have ascii file names too, as seen by dir /x. Which may help in some cases, transparently recognized as the alias of the Unicode file name. E.g. Avisynth can read Unicode file names if you use such short (ascii) names.
@Masutin
Not sure if this will help you with your specific problem, but if you just open a file (e.g. MKV) with VirtualDub2, Keyframes are shows as scuh (Shift + arrow keys). You could also do ffmsindex.exe -f -k "path\to\your file.mkv" to quickly get the keyframe list.