Apple has just renewed its range of 14- and 16-inch MacBook Pros, as well as the Mac Mini. These machines inherit the M2 Pro processor which, in addition to being faster than the M2 already seen on the MacBook Air, now offers a more efficient HDMI output. Apple is not talking about HDMI 2.1, but this output supports 8K Ultra definition at 60 Hz and therefore offers the same bandwidth as HDMI 2.1. The HDMI output also supports an Ultra HD stream at 240 Hz, a definition/frequency combination hitherto unheard of in HDMI.
Indeed, the HDMI 2.1 standard has introduced compatibility with Ultra HD 120 Hz (4K120) streams, essential for playing at a high frame rate and very high definition on the latest generation consoles (PS5, Xbox Series X). However, it is less known, HDMI 2.1 also supports DSC (Display Stream Compression) which is none other than the compression of the video signal without any loss of visual quality. The HDMI Forum documents do not mention 4K 120 Hz, but mention for example the possibility of reaching an 8K Ultra definition at 100 or 120 Hz using DSC. It is therefore assumed that Apple uses this system to reach 240 Hz in Ultra HD.
The Nvidia GeForce RTX 4080 and 4090 graphics cards, for example, use DSC to transmit an Ultra HD 240 Hz signal via DisplayPort 1.4a, but the HDMI port is still limited to Ultra HD 120 Hz. a that Apple uses — for the moment — the DSC via the HDMI output. There is also only one Ultra HD monitor that can reach a frequency of 240 Hz, the Samsung Odyssey Neo G8 S32BG850NU. Alas, the latter does not mention DSC support via the HDMI input. We asked Samsung the question and are waiting to find out if this monitor is compatible with DSC via HDMI.
Support for HDMI 2.1 VRR, ALLM or QMS still unknown
Apple does not communicate on the HDMI 2.1 functions supported by the video output of its new computers equipped with the M2 Pro and M2 Max processors. Apple computers are well compatible with HDR10, HLG and Dolby Vision, but compatibility with VRR (Variable Refresh Rate) equivalent to FreeSync/G-Sync, ALLM (Auto Low Latency Mode, which reduces the display delay) or QMS (Quick Media Switching, which avoids black screens when changing sources), is not specified.