On my machine, if I play a 60FPS YouTube video such as https://www.youtube.com/watch?v=8PmM6SUn7Es in full screen mode, and have the FPS overlay enabled (layers.acceleration.draw-fps), the FPS overlay hovers around 52FPS. But the dropped frame count in YouTube's "Stats for nerds" overlay does not go up. Here's a profile: https://perfht.ml/34eK9UH You can see plenty of "NoCompositorScreenshot because nothing changed" markers: Those are frames where the composite was aborted because the image layer's image index hasn't changed since the last composite. But there are no corresponding "Video frames dropped" markers.
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On my machine, if I play a 60FPS YouTube video such as https://www.youtube.com/watch?v=8PmM6SUn7Es in full screen mode, and have the FPS overlay enabled (layers.acceleration.draw-fps), the FPS overlay hovers around 52FPS. This must mean that about 8 video frames do not make it to the screen, each second. But the dropped frame count in YouTube's "Stats for nerds" overlay does not go up. Here's a profile: https://perfht.ml/34eK9UH You can see plenty of "NoCompositorScreenshot because nothing changed" markers: Those are frames where the composite was aborted because the image layer's image index hasn't changed since the last composite. But there are no corresponding "Video frames dropped" markers.