Notes about the RCF file extension:
Incorrect file associations could be the result of underlying issues within your PC system. As such it is highly recommended to scan your PC for invalid registry entries, unused processes and other unfavourable system settings to identify slowdown issues.
The RCF file type is primarily associated with 'Rhapsody' by RealNetworks. Rhapsody is powered by RealNetworks’ caching/streaming technology. This technology splits (or distills) audio files into two asymmetric pieces during the encoding process. The larger piece (called the Residual Audio Data, or RAD) contains 99% of the audio data and is streamed and cached (in encrypted form) to the subscriber’s hard drive during initial song playback. The remaining 1% of the file (called the Essential Audio, or EA) is streamed from RealNetworks’ servers and united (or rendered) with the larger file at playback, enabling subscribers to hear the sound. This process is nearly instantaneous and is invisible to the subscriber.
A proprietary file called RADFILE.RCF holds the cache. On first play songs appear to stream from the Internet; on second play during a session, from the cache.