The rtsl file extension is related to RealNetworks, which utilize the IETF standardized Real Time Streaming Protocol (RTSP) but only to manage the connection. The actual audio data is sent with their own proprietary RDT protocol, which they initially kept secret. Recently, some specifications for the RDT protocol have been made public through the Helix Community project. The open-source MPlayer project eventually developed a means of playing the RDT streams.
MIME: application/x-rtsl Mime: application/x-rtsp
How to open:
This file type is not meant to be opened directly, there is no software that could open and work with it directly, or there is no information available in public sources about opening this file type. This is usually the case of some internal data files, caches, temporary files etc.
How to convert:
As far as we know, this .rtsl file type can't be converted to any other file format. This is usually the case of system, configuration, temporary, or data files containing data exclusive to only one software and used for its own purposes. Also some proprietary or closed file formats cannot be converted to more common file types in order to protect the intellectual property of the developer, which is for example the case of some DRM-protected multimedia files.