Add webm/rm/rmvb support

PR: 254379
Submitted by: Masachika Ishizuka <ish@amail.plala.or.jp>
Approved by: glebius (maintainer)
Obtained from: https://github.com/lqs/minidlna/commit/4189368bba79d944edb54d4c7d476565e98c3e8b