HDMI™ features some new tricks that allow for the improved transport of audio-video signals. One of these tricks is FRL, or Fixed Rate Link.

FRL differs from the traditional TMDS signaling of legacy HDMI versions (HDMI 2.0 and below). It defines signals by the number of lanes and their combined lane rates. There are nine possible FRL rates, consisting of three to four lanes each transmitting a lane rate of 3-24Gbps. Notably, FRL will always attempt to maximize throughput based on the sink capabilities and, ultimately, the link’s (cable’s) maximum capacity. It does this using link training, where each lane maintains a fixed data rate, unlike the varying data rates of legacy TMDS Channels. FRL embeds the Clock Channel directly into the HDMI signal, allowing for features such as Variable Refresh Rate, Dynamic HDR, and more.

However, newer versions of HDMI are not entirely different. Because FRL is backward compatible with lower data rates, HDMI will fall back to traditional TMDS if FRL is not supported. In this fallback mode, TMDS is capable of transmitting signals up to FRL2. Although a device may support a particular FRL rate, it may not support all possible video signals.