What is HDMI and which versions are there?

HDMI also called High Definition Multimedia Interface, is use to transport digital high resolution video and multichannel audio over a single cable, it can also control TV and monitors through the cable.
HDMI is based on DVI, but HDMI can also transport audio in comparison to DVI.
It comes in different connectors:
Type A is a 19 pin connection
Type B is a 29 pin connector, which is compatible with dual link DVI
Type C is a 19 pin min connector

HDCP

Copy protection also called HDCP was introduced to HDMI in year 2000, it is a two way communication with in the i2C control interface, each time a HDMI is connected, a three-part authentificaion occurs:
1. shared values, or coeds between devices
2. the KSV of each receiver is reported to the source
3. Frame-by-frame ciphers are sent to the receivers that enable data decoding
HDCP uses a hierarchy of sources, and all devices has to communicate, the hierarchy supports up to 7 levels of repeaters and up to 128 devices. When a source receives HDCP content it gets authenticated, decrypted and the re-encrypted before it gets transmitted to the next source.

CEC

CEC – Consumer Electronics Control is a plug-and-play to control devices connected via HDMI, it can be a videoconference system controlling the monitor or similar.
CEC was introduced with HDMI version 1.2a

The difference between the HDMI versions:

HDMI 1.1: support for DVD audio
up to 8 channels of 192 kHz/24 bit audio (PCM)

HDMI 1.2: support for 1-bit audio
HDMI type a connectors
HDMI version 1.2a CEC

HDMI 1.3: bandwidth up to 340 MHz which gives higher resolution and deeper color.

HDMI 1.4: HDMI ethernet channel (can send and receive 100 Mb7sec ethernet)
Audio return channel
3D is supported with 3D in dual-stream 1080p
4Kresolution
Expanded support for color spaces
Type D micro connector

HDMI 2.0: Also called HDMI UHD
4:2:0 chroma sampling
up to 32 channels of audio
Additional CEC functions