Refresh Rate

While this website is focused on the latency added by sink devices, there are some modes on the transport interface relating to refresh rate that have a considerable impact on the overall time between when a user performs a physical input and when the resulting output is presented as light and sound.

Put simply, a higher refresh rate will reduce the overall latency of a complete input-to-output system. This benefit is primarily seen in video, but a video game may be able to produce resulting audio faster with a higher refresh rate by performing its game state updates more often. To reduce this overall input-to-output latency a higher refresh rate should always be recommended when a source is capable of providing it.

In addition to a higher refresh rate, there are two other relevant modes common to transport interfaces such as HDMI and DisplayPort: Variable Refresh Rate (VRR) / Adaptive Sync and Quick Frame Transport (QFT).

Note: The benefit of higher refresh rates, VRR, and QFT can be calculated and are constant for all sink devices because they are modes of the transport interface. Audio and video latency are independent of the transport interface and the benefits provided by these modes.

Input lag measurements include a portion of the benefit gained from these transport interface modes, but do not include benefits such as those from a video game performing its game state updates more often.

Variable Refresh Rate (VRR) / Adaptive Sync

This transport interface mode allows a refresh rate to dynamically change on a per-frame basis, up to a maximum refresh rate, based on when a frame is ready to be transported. This mode is primarily relevant to video games which may take a variable amount of time to prepare a frame of video.

Quick Frame Transport (QFT)

This transport interface mode enables a constant refresh rate with faster transport of frame data while increasing the duration of the vertical blanking interval. After a video source has completed preparation of a frame of video, this mode allows the video frame to be fully presented on a display more quickly than with a standard refresh rate, thus reducing the average overall time between a user’s input and its resulting video output.

Author’s note: as of June, 2021 I don’t know of this feature being widely used in any consumer devices. Please let me know if you know of any examples of when this feature is used!

Last updated on October 8th, 2021.