CDXL is motion video

file format A file format is a standard way that information is encoded for storage in a computer file. It specifies how bits are used to encode information in a digital storage medium. File formats may be either proprietary or free. Some file formats ...

developed by Commodore in the late 1980s and early 1990s for the

Amiga Amiga is a family of personal computers introduced by Commodore in 1985. The original model is one of a number of mid-1980s computers with 16- or 32-bit processors, 256 KB or more of RAM, mouse-based GUIs, and significantly improved graphi ...

computer platform. It is notable for being one of the earliest formats created for motion video playback from

CD-ROM A CD-ROM (, compact disc read-only memory) is a type of read-only memory consisting of a pre-pressed optical compact disc that contains data. Computers can read—but not write or erase—CD-ROMs. Some CDs, called enhanced CDs, hold both comput ...

Background

In an era shortly after the introduction of CD-ROM drives and before low cost MPEG decoding hardware became available the CDXL format was created, primarily for the Commodore CDTV, to permit playback of video from CD-ROM. CDXL is tailored for the Amiga chipset and takes advantage of

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transfers, thus achieving playback with a low

CPU A central processing unit (CPU), also called a central processor, main processor or just processor, is the electronic circuitry that executes instructions comprising a computer program. The CPU performs basic arithmetic, logic, controlling, and ...

load. As a result, CDXL can only support weak

video compression In information theory, data compression, source coding, or bit-rate reduction is the process of encoding information using fewer bits than the original representation. Any particular compression is either lossy or lossless. Lossless compression ...

and therefore relatively low video resolutions and moderate

frame rate Frame rate (expressed in or FPS) is the frequency (rate) at which consecutive images (frames) are captured or displayed. The term applies equally to film and video cameras, computer graphics, and motion capture systems. Frame rate may also be ca ...

s. CDXL is a simple streaming format, consisting of linear concatenated chunks (packets), each with an uncompressed frame and associated audio data. There is no overall file header, just a header per chunk. The frame rate is constant but not stored in the file, so it is necessary to set the playback speed in the player software manually. The CDXL format initially allowed playback of up to 24 frames per second with up to 4096 colors encoded in HAM-6. Audio support allows for 8-bit mono or stereo sound. With the advent of the Amiga CD32, the CDXL format has been extended to support AGA color modes (up to 262,144 on-screen colors from a 24-bit color palette) and higher display resolutions.

Usage

A number of Amiga CD-ROM games and entertainment software uses CDXL for motion video. CDXL is supported by AmigaOS through its datatype system, which allows playback of CDXL files on compatible systems.

Performance

Playback performance can be thought of as impressive at the time of release given the CDTV's

Motorola 68000 The Motorola 68000 (sometimes shortened to Motorola 68k or m68k and usually pronounced "sixty-eight-thousand") is a 16/32-bit complex instruction set computer (CISC) microprocessor, introduced in 1979 by Motorola Semiconductor Products Sector ...

processor, OCS chipset and single-speed CD-ROM drive constraints. A single-speed (150 kB/s) CD-ROM drive permits resolutions equivalent to 160×100 with 4,096 colors at 12 frame/s with 11025 Hz 8-bit mono audio. At these settings audio and visual quality is perceived as considerably worse than VHS. A CDXL stream at 300 kB/s (equivalent to 256×128 at 12 frame/s) allows approximately 36 minutes of video to fit on CD-ROM. In comparison, a Video CD encoded in MPEG-1 format allows approximately 72 minutes of 352×288 (PAL) 24-bit color video at 25 frame/

External links

CDXL player software

References

{{DEFAULTSORT:Cdxl Graphics file formats Amiga Computer file formats Digital container formats Film and video technology