Question

I use following keyframe animation on several elements:

@keyframes redPulse {
    from { background-color: #bc330d; box-shadow: 0 0 9px #333; }
    50% { background-color: #e33100; box-shadow: 0 0 18px #e33100; }
    to { background-color: #bc330d; box-shadow: 0 0 9px #333; }
}
@-webkit-keyframes redPulse {
    from { background-color: #bc330d; box-shadow: 0 0 9px #333; }
    50% { background-color: #e33100; box-shadow: 0 0 18px #e33100; }
    to { background-color: #bc330d; box-shadow: 0 0 9px #333; }
}
.event_indicator {
    display: inline-block;
    background-color: red;
    width: 5px;
    margin-right: 5px;

    -webkit-animation-name: redPulse;
    -webkit-animation-duration: 1s;
    -webkit-animation-iteration-count: infinite;

    animation-name: redPulse;
    animation-duration: 1s;
    animation-iteration-count: infinite;
}

On my computer I am getting around 40% CPU usage both in Chrome and Firefox.
Is it the current state of animations (nice but not usable for now) or am I missing some magic property?

You can check the following sample with the same animation:
http://jsfiddle.net/Nrp6Q/

Answer 1

Yes, this is normal because you have several infinite-loop animations on the page. The CPU is therefore continually doing work while these elements are rendered. There is a “magic” property that will significantly cut-down the CPU usage and that is:

transform: translateZ(0);

This will composite the elements into their own layers (by tricking the browser into thinking it will be doing 3D transforms) and the browser should, in most cases, take advantage of GPU acceleration, lessening the burden on the CPU. For me this cut it down by about 20% (almost half).

To read more about this technique take a look at: http://ariya.blogspot.com/2011/07/fluid-animation-with-accelerated.html

Additionally, the more keyframes you have in the animation, the more taxing it will be as well. Just try the animation with the middle keyframe cut out and you will see another substantial (~10-12%) drop in CPU usage.

Lastly, not all properties are equal — box-shadow is much harder for the browser to animate smoothly than, say, background-color. Leaving all of the keyframes intact but dropping the box-shadow property, using the translateZ(0) trick had my CPU usage hovered at only 10-11%.

As much as it pains me to say this, for infinite-loop animations an animated .gif is going to perform much, much better than CSS3 in the current state of browser animation, especially if you plan for many of them to remain rendered on the page for some time.

Update 2017:

For those still finding their way to this question and answer, translate3d(0, 0, 0) provides the same benefit as translateZ(0), you’re just also setting translateX() and translateY() at the same time. Please ignore the comment by @Farside as he uses translate3d(X, Y, Z) in his demo but does not compare it to translate(X, Y), which would show that using this technique still makes a significant difference.

According to this question, some people have found better performance across all browsers, especially Chrome, with transform: rotateZ(360deg).