HDMI 2.1

HDMI 2.1 was released by the HDMI Forum in January 2017, more than four years after HDMI 2.0. The Forum has managed the HDMI specification since 2011, taking over from the original group of seven founding companies that created HDMI in 2002.

The jump from HDMI 2.0 to 2.1 nearly tripled maximum bandwidth, from 18 Gbps to 48 Gbps, by introducing a new signaling method called Fixed Rate Link (FRL) in place of the older TMDS (Transition-Minimized Differential Signaling) used since HDMI 1.0. That bandwidth increase is what makes 4K at 120Hz and 8K at 60Hz possible without relying on compression for most content.

HDMI 2.1 introduced several gaming- and audio-focused features earlier versions lacked. Variable Refresh Rate (VRR) lets the display's refresh rate match the source's frame rate to reduce stutter and tearing, and Auto Low Latency Mode (ALLM) lets a console or PC automatically switch a TV into its lowest-latency game mode.

On the audio side, enhanced Audio Return Channel (eARC) replaced the original ARC, raising bandwidth enough to carry object-based surround formats like Dolby Atmos and DTS:X in their full, uncompressed form from a TV back to a soundbar or receiver -- something the original ARC's limited bandwidth couldn't support.