.rm Video File Format
According to the Wikipedia page on the subject, "RealMedia is a multimedia container format created by RealNetworks. Its extension is ".rm". It is typically used in conjunction with RealVideo and RealAudio and is used for streaming content over the Internet in a constant bitrate."
RM files use both progressive encoding and streaming technology. Progressive encoding requires viewers to download a video file in its entirety before being able to view any of its content. Streaming technology enables viewers to watch portions of video footage without downloading the entire file, a nice feature that allows viewers to review footage after only a few seconds.
RM files also use temporal compression, which reduces the amount of data stored within a sequence of frames by employing key frame technology. Rather than storing every pixel in each frame, temporal compression stores a key frame, the only the information which is changing between key frames. Quality of the footage can be significantly lower than progressive encoding formats as a result of temporal compression being used. Temporal compression also has the drawback of not allowing future editing of the file.
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