This report defines two aspects of a method for delivering closed captions over IP-transported programming. First is the definition of an MP4-based media file format, called the Reference File Format (RFF) in which the file contains video, audio, and captioning in SMPTE-TT format. The second is a specification of technical details of a player capable of rendering the video and subtitles contained in files conforming to the specified format. This player is called a “Reference Media Player” or RMP. Further, this report describes certain features and capabilities of the RMP, in particular its ability to render closed captioning and to offer the user certain controls over caption display and operation.