The High Definition Multimedia Interface is a standard interface to be found in many audiovisual equipment including High Definition Television and home theater systems. It is mainly used in transmission of digital streams. This is a cable that looks like a USB wire. It can carry bandwidth of around 5 Gbps, which is almost twice the bandwidth necessary for transmitting multichannel audio as well as video for the foreseeable future. HDMI cuts down the number of cables used to connect components and even reduces the number of remote controls necessary to watch a movie. However, in order to take advantage of all that HDMI has to offer, all the home theatre components have to be compatible with HDMI. Some of the features offered by HDMI are yet to take off in the consumer marketplace. The HDMI cable can only be so long, and many customers complain that this leads to inconvenience. HDMI is really a brainchild of the major consumer electronic manufacturers, who had the objective of simplifying the task of connecting and synchronizing the available High Definition (or simply HD) for the benefit of their customers. The electronic firms, mainly comprising Japanese and South Korean heavy hitters, hoped that the synergies in their joint efforts would enable users of their components to connect them without having more than a superficial knowledge of electronics.
There is a popular misconception among many people that anything digital will always be superior to the analogue signal, which is seen as anachronistic. This school of thought also propagates that the lack of analog-to-digital conversion means that the signal is pure and undamaged once it reaches the High Definition TV set. However, even a digital transmission needs an encoding step. And so HDMI uses Transition Minimized Differential Signaling (TMDS) to move information from one place to another. TMDS protects the integrity of the signal so that it does not become degraded as it travels through the cable. So, one of the wires in the cable carries the original signal, while another carries the inverse copy of the signal. The device that is meant to receive the signal, for instance, High Definition Television, decodes the signal, and then measures the difference between the signal and its inverse (called differential). The information then gathered can be used to compensate for any loss of signal along the way.
HDMI is also employed effectively to protect data from piracy, and for this, it uses high-bandwidth digital copy protection (HBDP). HDCP is basically an authentication protocol. Every home theatre has encryption and identification data stored on the EDID (extended display identification data) chip. So when a source device, such as the Blu-Ray player, confirms the authentication key of the receiving device, which can be a High Definition TV set, it also shares a secret key with the receiving device in a process called a handshake. The source code would then “wrap” the information using the shared key, and the receiving device decodes, or if you like, “unwraps” the information using the shared key. So, if some unauthorized device tries to eavesdrop or in any way tamper with the data, the source device would stop transmitting immediately.
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