8 mm video
The 8 mm video format refers informally to three related videocassette formats for the NTSC and PAL/SECAM television systems. These are the original Video8 (analog) format and its improved successor Hi8 (both analog and digital), as well as a more recent digital format known as Digital8.
Their user-base consisted mainly of amateur camcorder users, although they also saw important use in the professional field.
The format was created and launched in 1984 by Eastman Kodak . Kodak had designed a camcorder based on the format but Kodak withdrew from the market very early before it was established.
In 1985 Sony of Japan introduced the Handycam, one of the first Video8 cameras with commercial success. Much smaller than the competition's VHS and Betamax video cameras, Video8 became very popular in the consumer camcorder market.
The three formats (Video8, Hi8 and Digital8) are physically very similar, featuring both the same tape-width and near-identical cassette-shells measuring 95 x 62.5 x 15 mm. This gives a measure of backward-compatibility in some cases. One difference between them is in the quality of the tape itself, but the main differences lie in the encoding of the video when it is recorded onto the tape.
Video8 was the earliest of the three formats, and is entirely analog. The 8 mm tape width was chosen as smaller successor to the 12mm Betamax format, using similar technology (including U-shaped tape loading), but in a smaller form factor and in response to the small form factor VHS-C compact camcorders introduced by the competition. It was followed by a version with improved resolution, Hi8. Although this was still analog, some professional Hi8 equipment could store additional digital-stereo PCM sound on a special reserved track.
Digital8 is the most recent 8 mm video format. It retains the same physical cassette shell as its predecessors, and can even record onto Video 8 (not recommended) or Hi8 cassettes. However, the format in which video is encoded and stored on the tape itself is the entirely digital DV format (and thus very different from the analog Video8 and Hi8). Some Digital8 camcorders support Video8 and Hi8 with analog sound (for playback only), but this is not required by the Digital8 specification.
In all three cases, a length of 8 mm-wide magnetic tape is wound between two spools and held within a hard-shelled cassette. These cassettes share similar size and appearance with the audio cassette, but their mechanical operation is far closer to that of VHS or Betamax videocassettes. Standard recording time is up to 180 minutes for PAL and 120 minutes for NTSC. (The cassette holds the same length tape – tape-consumption is different between PAL and NTSC recorders.)
Like most other videocassette systems, Video8 uses a helical-scan head-drum to read/write video to the magnetic tape. The drum rotates at high speed (one or two rotations per picture frame – about 1800 or 3600 rpm for NTSC, and 1500 or 3000 rpm for PAL) while the tape is pulled along the drum's path. Because the tape and drum are oriented at a slight angular offset, the recording tracks are laid down as parallel diagonal stripes on the tape.