What is RMJ file? 

Real Jukebox file
File extension: .rmj
MIME type: application/vnd.rn-realsystem-rmj, application/vnd.rn-rn-taiko-real-rmj
Developed by: RealNetworks
Type of format: audio file format

WAV File Extension

Waveform
File extension: .wav
MIME type: audio/wav
audio/wave
audio/x-wav
Type code: WAVE
Uniform Type Identifier: com.microsoft.waveform-​audio
Developed by: Microsoft & IBM
Type of format: audio file
Extended from: RIFF

Convert RMJ to WAV with Mini-stream Ripper