People often fret over getting the right version of cables for electronics products, and HDMI is no different. Although few differences between versions matter to the average consumer, the difference between versions 1.2 and later versions is important to understand.

Bandwidth Differences

Earlier versions (1.2 and prior) of HDMI are limited to a maximum overall bandwidth of 4.9 gigabits per second (Gbps). Later versions (1.3 and later) upped this to 10.2 Gbps, which is still the standard today. This is the primary difference in HDMI cables.

Letters Don't Matter

If the HDMI cable specification lists a letter in its version (a, b, or c) this refers only to testing specifications and will have no bearing on the function of the cable.

Other Video Upgrades

Other, more minor video upgrades took place between versions as well, such as additional support for "Deep Color," a 30-, 36-, or 48-bit video interface, added in version 1.3, up from 24-bit in previous versions. Additionally, 1.4 offers extended resolution ranges, up to 4096 x 2160 pixels.

Other Audio Upgrades

Support for "One Bit Audio" was added in HDMI version 1.2. Version 1.3 saw the introduction of other minor audio upgrades and additions, such as support for output of Dolby TrueHD and DTS-HD Master Audio streams.

Other Upgrades

HDMI version 1.4 also includes a built-in Ethernet channel, allowing a connection speed of 100 MB per second (MBps) between the source and output devices.

HDCP Compliance

"HDCP Compliance" means that the cable meets High-bandwidth Digital Content Protection standards. HDMI cables are, by default, compliant to HDCP standards.

Source:

Lenkeng: HDMI 1.0 vs 1.2 vs 1.3 vs 1.4

Blue Jeans Cable: What Do These HDMI Spec Versions (1.2, 1.3, 1.3a, etc) Mean?

HDMI.org: Knowledge Base