FileInfo.com - The File Extensions Resource

.R1M File Extension

File Type	RealOne Streaming Media File
File Format	File
Common?	No
File Description	Temporary file saved by RealPlayer or RealOne Player when a streaming media file is downloaded from the Internet; created as a buffer when the media file is being streamed by RealOne Player; not meant to be opened by the user.
Program(s) that open r1m files	Mac / Windows: RealNetworks RealPlayer

Information from FileInfo.com - The File Extensions Resource.
http://www.fileinfo.com/extension/r1m