Variable Frame Rate Technology — Change Is Good!

For over 100 years the motion picture industry has worked to ensure stable frame rates from capture to screen. This was essential when content creation and display were separated by many steps, and mechanical and electronic devices were slow to synchronize to a new rate. Today's content can be multi-rate or rendered on the end consumer's device, and this has consequences. A frame which is not available at the expected time must either be replaced with a repeat, causing motion judder, or switched part way through a sync cycle, causing tearing. Adding enough processing power or bandwidth to guarantee a constant frame rate with arbitrary content is too expensive for the consumer world. — HDMI and DisplayPort standards support holding the current displayed frame until the next frame is ready, then switching quickly. This maintains smooth motion by delivering the delayed frame quickly, without waiting longer for a fixed sync. As an example, at a target frame rate of 60 fps, a 1ms delay can trigger a full frame repeat at 30 fps with a 17ms delay, causing excessive judder. With variable frame rate technology, the frame is delivered just 1ms late for an effective 57 fps rate. — This paper shows how delayed frames lead to judder, the changes required to implement variable frame rates, and the user benefits. Previously delivered in Graphics Processing Units (GPUs) and monitors incorporating AMD FreeSync, it is now available in TVs and gaming consoles, making it accessible to new applications.

Published

2018-10

Content type

Original Research

Keywords

Display, Frame Rate, FreeSync, Judder, Tearing, HDMI, DisplayPort, VESA, VRR, VFR

DOI

10.5594/M001823

ISBN

978-1-61482-960-7