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What is HDMI?
HDMI stands for High Definition Multimedia Interface, it is a universal connection like Scart however unlike Scart it carries High Definition Video content and Digital sound.
The connector is a 19pin mini plug and measures only 21mm wide.
HDMI transfers audio data frequencies up to 192 kHz with a word width up to 24 bit on up to 8 channels. The band width for video data is at up to 165 MHz. Therefore it is possible to project all picture and sound formats of the home cinema world - including HDTV (up to the highest resolution of 1080p) - without any loss of quality.
HDMI is based on DVI and is 100% downwards
compatible to DVI, which means that DVI-signals (via DVI-HDMI-adaptor-cable) can
be transferred via HDMI-interface. However, in the other direction only a subset
of the HDMI-signals is transferred to the DVI-interface. Both are compatible
because HDMI uses the same copy protection procedure as DVI: HDCP (High
Bandwidth Digital Content Protection).
HDMI also permits a bi-directional data transfer. Diverse advantages arise for the user due to this possibility. Only one example: A digital television set or AV-receiver is able to transfer its current picture- and sound adjustments (like e.g. 16:9 or 4:3/letterbox or 5.1 or 2-channel-stereo) to a digital Sat-receiver. Then the digital Sat-receiver transfers its digital information automatically in the appropriate adjustment.
Does HDMI accommodate long cable lengths?
Yes. HDMI technology has been designed to use standard copper cable construction at long lengths. In order to allow cable manufacturers to improve their products through the use of new technologies, HDMI specifies the required performance of a cable but does not specify a maximum cable length. Cable manufacturers are expected to sell reasonably priced copper cables at lengths of up to 15 meters. As semiconductor technology improves, even longer stretches can be reached with fibre optic cables, and with active cable technologies such as amplifiers or repeaters.
No, they aren't, since one feature of HDMI called HDCP (High-bandwidth Digital Content Protection) is precisely which has to prevent this. HDCP will only be decoded in the receiving, as a rule in the picture-reproducing component. Recording appliances, like e.g. hard-disk recorders will not be equipped with a HDCP-decoding algorithm. The modification of components or the trade with modified components is a punishable offence according to the new copyright law which came into force on October 1st, 2003. So the production of digital copies will not be possible or be at least effectively prevented as the HDMI-inventors see it. Right from the beginning this was a prerequisite that the "majors" of the Hollywood Studios like Fox or Universal agreed to support HDMI. Only this support got HDMI generally accepted.
Is HDMI compatible with DVI?
Yes. HDMI is based on DVI and is 100% downwards compatible to DVI, which means that DVI-signals (via DVI-HDMI-adaptor-cable) can be transferred via HDMI-interface. However, in the other direction only a subset of the HDMI-signals is transferred to the DVI-interface. Both are compatible because HDMI uses the same copy protection procedure as DVI: HDCP (High Bandwidth Digital Content Protection).