When it renames the youtube video, it sometimes removes characters that NTFS can handle and replaces them with underscore (_). Would love to see those characters being used in the name.

Second, support of illegal character replacements. If the filename has an illegal character, do not replace it with just an underscore but an equivalent Unicode character or allow the user to have a list of replacement characters.

Bellow is full list of illegal NTFS characters and their functioning alternatives:
" = ＂
? = ？
: = ：
/ = ／
\ = ＼
* = ＊
> = ＞
< = ＜

[raztoki]