HDMI is a one-cable way to connect high-definition AV components and is currently the most common connection method used on Blu-ray players, AV receivers, cable/satellite set-top boxes, gaming consoles, and video displays such as plasma/LCD TVs and front projectors. HDMI can pass high-definition video and high-resolution, multichannel audio (including the DTS Master Audio and Dolby True HD soundtracks found on many Blu-ray discs) over a single cable, providing an easy, uncluttered way to connect your devices.
HDMI has been through many upgrades in its lifetime. You can read about previous versions through the HDMI Wikipedia page or at HDMI.org. The current spec, officially announced in 2017, is HDMI 2.1, which increases bandwidth up to 48 Gbps and supports the passage of a 4K/Ultra HD resolution at up to 120 frames per second and resolutions up to 10K (10,420 x 4,320) with transmission compresion. Other enhancements in the 2.1 spec include support for variable refresh rate, quick frame transport (for reduced latency), quick media switching, and some technologies -- like Enhanced Audio Return Channel and Auto Low Latency Mode -- which were added to HDMI 2.0 devices before HDMI 2.1 hardware was available. HDMI 2.1 is now appearing on the new crop of 8K TVs and will be the connection format of choice for upcoming video game consoles like the PlayStation 5 and Xbox Series X.
Speaking of cables, HDMI Licensing, LLC has defined six different types of HDMI cables; officially licensed HDMI cables should clearly identify their type on the packaging to help you select the kind you need:
Standard HDMI Cable with Ethernet: offers the same baseline performance as the Standard HDMI Cable with an additional, dedicated data channel, known as the HDMI Ethernet Channel, for device networking.
Standard Automotive HDMI Cable: supports up to 720p/1080i. Since an automotive system may be wired with one or more internal relays that can affect signal strength, the Standard Automotive HDMI Cable needs to send a stronger signal than other cables types, so it is tested to higher performance standards.
High Speed HDMI Cable: tested to handle video resolutions of 1080p and beyond, including 4K, 3D, and Deep Color. This type of cable is recommended for use with a 1080p Blu-ray player or gaming console, as well as new Ultra HD gear.
High Speed HDMI Cable with Ethernet: offers the same baseline performance as the High Speed HDMI Cable with an additional, dedicated data channel, known as the HDMI Ethernet Channel, for device networking.
Ultra High Speed HDMI Cable: supports increased bandwidth up to 48 Gbps and transmission of 4K 8K video signals, as well as new features such as eARC and Variable Refresh Rate.
While HDMI is a very convenient way to connect devices, the technology is not problem-free. HDMI employs HDCP copy protection to protect the digital information transferred between devices; the connected devices must establish HDCP authentication in order to transmit the signal, which is sometimes called the HDCP handshake. If the handshake is unsuccessful, you may see a blue or otherwise discolored image, or you may just see snow on the screen. Handshake issues are less common than they were in the early days of HDMI, but they still occur. To re-establish the HDCP handshake between two devices, you can try disconnecting and reconnecting the HDMI cable at each end and/or powering down the components and restarting.
HDMI can also be less reliable over long runs. If your AV gear sits only a few feet away from your TV, then a basic, inexpensive HDMI cable will likely do the job just fine. However, if you need to run HDMI across the room to a projector or through walls to an equipment room, then you'll probably need to step up to a well-built active HDMI cable that boosts the signal to extend the range, up to about 100 feet. RedMere is one chipset used in some active HDMI cables. For even longer runs, consider an HDMI Extender Kit from a company like Gefen, Atlona, or WireWorld that can send the signal over CAT5/6, coaxial, or fiberoptic cable.