From RWilson Fri Nov 26 13:13:24 1993
Path: doc.ic.ac.uk!uknet!acorn!not-for-mail
From: RWilson
Newsgroups: comp.sys.acorn
Subject: Replay/ARMovie corrections
Date: 26 Nov 1993 11:03:33 -0000
Organization: "Acorn Computers Ltd, Cambridge, England"
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Recently Adam Curtin (hi, Adam) {adam@ifeng.demon.co.uk} said:

> I don't know where you got the bit about sending the video to Eidos to be
> compressed - you just plug your VCR into Compressor and click the record
> button ... the compression's 25fps in real-time. Perhaps we lent nott.ac.uk
> an Optima but not a compressor back in the dim distant past, or maybe you're
> thinking of Acorn's Moving Lines compression for Replay, where you have to
> take your video to specially appointed compression centres - because Moving
> Lines compression takes several seconds per frame (what is it now Roger? 5s?
> 30s?) and requires an Arc hooked up to a tape machine with transport control
> so it can make the necessary twelve zillion passes through the tape.

which I feel puts a very unfair light on the current state of making Replay
files, even though it was true two years ago.

Both Irlam and Computer Concepts sell hardware which records direct to disc
16 bit per pixel live video with stereo sound at (say) 160x128 12.5fps (CC's
hardware is more flexible than Irlam's which is fixed at this size) with
optional hardware antialiasing as the video is scaled from the original
capture. This makes an ARMovie file which can immediately be replayed, but
is kind of large (between 6 bits per pixel and 10 bits per pixel depending
on how you set the capture options).

Both companies supply the Acorn designed 'MovingLines' compressor which can
be as quick as 3-4 seconds per frame (33MHz ARM3, compressor in 'quality'
state) or as slow as 10-30 seconds per frame (slow CPU, compressor in CD-ROM
bandwidth limited state). The movie can be taken down to around 3 bits per
pixel without noticeable loss and to between 1.5-2.5 with what I'd call
'acceptable degradation' (you KNOW its compressed, but it doesn't detract
>from the sequence's impact). Sequences on the Acorn VideoClip collection 1
CD-ROM have, of course, been compressed for CD-ROM bandwidth.

Uniqueway still provide the capability to do this for you - they have higher
quality capture systems and gallons of video processing hardware - if you
want something different.

Replay decompression can be on any machine with more than 1.4M (or
thereabouts) free. The decompressor (!ARMovie directory) is supplied by
Acorn and is capable of painting onto 1-24bpp screen depths and of following
shaped output (e.g. the movie is decompressed onto a rotating 3d model of an
acorn). Decompression is more efficient than compression or capture: the
movies at Acorn World were 320x200 pixels at 15fps, decompressed with 2:1
scaling. On 16 and 24 bpp displays, bilinear interpolation is used to
improve the quality of the 2:1 scaling. Apart from device drivers that hog
the CPU (no names, no packdrill), decompression works from any storage media
that has sufficient bandwidth: CD-ROM, IDE, SCSI, NFS, AUN Ethernet... ARM2
machines (A3000, A3010) can handle 12.5 fps (A3000 in mode 15, A3010 in mode
28). ARM3 machines can handle 25 fps (8MHz MEMC in mode 15, 12MHz MEMC in
mode 28).

Replay sound is available in mono/stereo, 4 bit ADPCM, 8 bit signed linear,
8 bit unsigned linear, 8 bit VIDC exponential format, 16 bi linear. Movies
can have any number of sound tracks, the first one being played by default.

Demos available, but not over the Internet: a 1 minute compressed movie can
be 7-15 MBytes (depending on picture size, frame rate and quality).

--Roger