User:Trevj/Replay (software)

cf. REPLAY (software)

In computing, Replay is a multimedia framework developed by Acorn Computers, capable of handling various formats of digital video, picture and audio under RISC OS. It was written by Sophie Wilson and released in 1992 for the Acorn Archimedes.

The software allows RISC OS computers to play videos on the desktop or full-screen. When reported on by Jack Schofield in The Guardian in 1992, it was described as "the highlight" of the recent BETT exhibition. He added that it "looks better than QuickTime".

Features
Replay uses software decoding to render a 160x128 film at 25fps (ARM3) or 12.5fps (ARM2). Audio capability is for stereo sound of multiple channels.

Support for the file format was included before launch in packages such as Magpie and Genesis.

Components
Files can be played via !ARPlayer, a standard desktop application which installs itself on the icon bar. The playback of audio alone is facilitated via !MultiSound, and the software's codecs are available as system resources via !ARMovie.

Development
Work by Acorn on Replay 3 was reported in January 1996.

Codec
Use of the codecs for video capture with Irlam Instruments' Replay DIY expansion card typically result in one minute of raw video (around 37MB) being compressed to 5MB. The compression system used facilitates 25fps from hard discs and 12.5fps from slower media such as floppy disks and CD-ROMs. An 800k floppy disk could typically store 12 seconds of compressed video at 12.5fps.

The compression process employs lossy compression on each sprite, as individual frames. Delta encoding is then employed to remove further unneeded data.