Earlier this year, the HDMI Forum - the association that develops HDMI spec - released its plans for the new specification that promised refresh rates at 8K60Hz/4K120Hz, commercial 10K, dynamic HDR, 48 gigabits per second bandwidth, and a few more goodies. Despite the underwhelming upgrade name, the newer version is sure to make a huge impact.
The biggest note here is the Ultra High Speed HDMI cable that tops out at 48Gbps, and are backward compatible with older HDMI specs. Yes, the new 2.1 spec will fit all current builds without having adapters or dongles. The current iterations are quadrupled and doubled with 10.2Gbps at HDMI 1.4, and 18Gbps at 2.0 respectively. The bigger bandwidth will give integrators more room to send uncompressed 4K video at "up to 120 frames per second," with 12 bits per channel high dynamic range color. Even at 30fps, the new spec supports uncompressed 8K 12-bit and 60fps using chroma subsampling.
HDMI 2.1 is also releasing a feature dubbed Display Stream Compression, that lets video streams surpass the 48Gbps limit by compressing images on the fly. HDMI Forum notes that it can reach up to 128Gbps, for chroma subsampled 120fps 12-bit HDR 8K video.
The new spec also supports an enhanced refresh rate that uses a few different technologies that can eliminate lag (Variable Refresh Rate), move quickly between videos to reduce blank screens (Quick Media Switching), and reduce latency for smoother video game play (Quick Frame Transport).
Another impressive feature is eARC technology allows TVs and audio equipment (receivers, soundbars, etc) to communicate over the same HDMI cable. The massive 48Gbps allows the audio to send newer audio signals over the same line. While ARC technology basically does just that, the limited bandwidth topped out at DVD-quality audio. DTS:X, Dolby Atmos, uncompressed 5.1 and 7.1 audio, as well as DTS Master and Dolby TrueHD, are all welcome on the new spec.
Without diving too much deeper into the new spec, it's obvious that HDMI is ready for an update like this. While 4K content hasn't quite hit mainstream consumer usage, although it is admittedly very close, having the capabilities to hit the next few levels at insane refresh rates is, in a word, refreshing. The newest built-in tricks will really begin to show-off the capabilities of wide-spread HDR adoption as well as comfortably managing high-end audio needs. All that and you don't even have to retrofit.
The HDMI Forum expects UHS HDMI cables to be released by Q2 2018 after it complies with the HDMI 2.1 Compliance Test Specification.