A Tale of Two Frame Rates

I had the good fortune of attending a local SIGGRAPH chapter talk by Bruna Berford of Penrose Studio, regarding production methodology and how they approached animation in their beautiful and emotionally compelling VR experience “Alumette”. She presented a good view into the difficulties, challenges,and rewards of adapting to working in this new medium. And let me say that to my thinking, they are actually embracing the new technology fully as a narrative medium.

But that’s not what this post is about. This post is about a misconception that people in V/M/AR have around the concept of frame rate. Specifically the holy grail of a 90+ fps redraw rate. This is held up as a metric which must be achieved for a non-nauseating viewing experience and is usually stated as an across the board dictum. Alumette, however, threw a very nice wrench into that, one which points to something that I’ve tried to articulate in the past. There are two different frame rates going on here. And that difference is apparent in Penrose’s use of stop motion frame rates for its animation.

The first “frame rate” is the one is the one that’s usually meant and I think of that as being the perceptual, or maybe even proprioceptural frame rate. This is the frame rate that corresponds to how well the environment is tracking your body’s movements. For instance when you turn your head, or when you walk around in a room scale experience. This is the one that tells your lizard brain whether or not you are being lied to. But a lot of people, including seasoned veterans, stop here, assuming that the matter is settled, but I think there’s a second frame rate at work.

The second is what I would call the exterior frame rate. This is the frame rate of the displayed content. And in Alumette this was definitely not at 90+ fps. In fact it was at a consciously much “slower” and less constant frame rate because it was being animated on hard, held keys with no interpolation. This was to emphasize the poses of the animation. The result was an elegant reference to traditional stop motion animation, with all of the artistic start/stop and a wonderfully surreal sense of time. And the overall experience in VR was not so much watching a stop motion animation, but rather existing in space with one. It was pretty cool.

The “content” was running at what I night guess averaged to ~12 fps, but the display of it, and therefore more importantly my perception of the experience was at the magic 90+ fps. This is an important distinction – especially when it comes to content creation. Would 360 video at a lower playback rate, say 18 fps, give us that old Super8 home movie feel as long as the the video sphere it’s projected onto was moving seamlessly? Could a game engine environment be optimized to hold frames of animation at 30fps allowing temporally redundant data to limit draw calls or GPU memory writes?


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Over 20 years of experience in creative/technical supervision and design in Visual Effects, Feature Animation and Scientific Visualization.

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