how to play rv10 .mkv video files?

[XXXXXX]

which plug-in/video player is needed?

 

[xtknight]

Media Player Classic and Haali splitter?

You are playing RV10 within Mastroska container?

RV10 as in RealVideo 10 or RealVideo 1.0? If that's the FourCC, it's RealVideo 1.0 and that should be playable by Media Player Classic. If it's RealVideo 10, the FourCC is RV40 AFAIK.