UPDATE: Change committed on #785. Please see #375 instead (rewritten/newer) for further standardization efforts on this.

PROBLEM

• requestAnimationFrame() is not sufficiently rigidly enough defined.

The older W3C "Animation Timing" spec had a better definition (https://www.w3.org/TR/animation-timing/) Section 5 says "The expectation is that the user agent will run tasks from the animation task source at at a regular interval matching the display's refresh rate. Running tasks at a lower rate can result in animations not appearing smooth. Running tasks at a higher rate can cause extra computation to occur without a user-visible benefit."
-- However the newer W3C HTML 5.1 no longer correctly describes the desire to match requestAnimationFrame() exactly to the refresh rate.

DETAIL

• Browser support of refresh rates are mostly consistent except for a few browsers:
  http://www.testufo.com/browser.html
• Some browsers use an arbitrary hardcoded framerate limits (e.g. 105fps), such as found in Microsoft Internet Explorer:
  https://connect.microsoft.com/IE/feedback/details/794072/internet-explorer-animations-fails-on-120hz-computer-monitors-works-at-60hz-75hz-100hz?siteID=rGMTN56tf_w-1PqoBW8wrx7DKpzuXQ.Wbg
• A listing of many problems with requestAnimationFrame() timing:
  http://www.vsynctester.com/howtocomputevsync.html and at http://www.testufo.com/browser.html
• Firefox issue where it intentionally computes incorrect VSYNC times:
  http://www.vsynctester.com/firefoxisbroken.html
• Differing amounts of time spent inside requestAnimationFrame() can create jerkiness/stutters or lower frame rates despite using only a fraction of CPU. There were some benchmarks done:
  http://www.blurbusters.com/blur-busters-120hz-web-browser-tests/
  Stutter began to occur in some browsers even at 10% CPU, while Chrome remained stutter-resistant all the way to 75% CPU used up (e.g. 12ms inside requestAnimationFrame() during a 1/60sec period). This disparity is unreasonable.

WHY IT IS IMPORTANT

• Games
• High-refresh-rate monitors (120Hz+ monitors, often found in GSYNC / FreeSync gaming monitors)
• Animations, motion tests, etc.
• Virtual reality. Note that Oculus/Rift is 90Hz

EASY SOLUTIONS

• Discourage hardcoding of numbers such as "60Hz" or arbitrary maximum framerates such as "105". This does a disservice to high-refresh-rate monitors and future HFR displays (including future 4K120Hz and 8K120Hz standards)
• Strengthen specification to make synchronization to display refresh rate a "MUST" instead of a "RECOMMENDED"
• Strengthen specification to make it return exact vsync time rather than now(). Chrome is the only one that does it correctly.
• [This lineitem has been moved to VSYNC API: Support for VSYNC OFF / 120Hz+ / variable refresh displays / etc #375] Strengthen specification to reduce allowable jitter, to permit smoother animations, given the increasingly real-time nature of websites, games, VR, etc. Things should be able to be stutter/jank-free all the way to ~50%-75% CPU used up inside requestAnimationFrame()
• [This lineitem has been moved to VSYNC API: Support for VSYNC OFF / 120Hz+ / variable refresh displays / etc #375] Add options of flexibility such as to maximize smoothness (when fluidity is priority) versus minimizing lag (when minimum latency is priority).

COMPLIANCE TESTING WEBSITES FOR requestAnimationFrame()

• http://www.vsynctester.com (click the gear icon for lots of tweakable settings)
• http://www.testufo.com/#test=animation-time-graph&easteregg=1

SUPERSEDES (IN PART): #422, #375, #159