Have you ever seen an animated GIF on a service like Imgur or Gfycat, inspected it in your dev tools, only to find out that GIF was really a video? There's a good reason for that. Animated GIFs can be downright huge.
Thankfully, this is one of those areas of loading performance where you can do relatively little work to realize huge gains! By converting large GIFs to videos, you can save big on users' bandwidth.
Measure first
Use Lighthouse to check your site for GIFs that can be converted to videos. In DevTools, click on the Audits tab and check the Performance checkbox. Then run Lighthouse and check the report. If you have any GIFs that can be converted, you should see a suggestion to "Use video formats for animated content":
Create MPEG videos
There are a number of ways to convert GIFs to video,
FFmpeg is the tool used in this guide.
To use FFmpeg to convert the GIF, my-animation.gif to an MP4 video, run the
following command in your console:
ffmpeg -i my-animation.gif -b:v 0 -crf 25 -f mp4 -vcodec libx264 -pix_fmt yuv420p my-animation.mp4
This tells FFmpeg to take my-animation.gif as the input, signified by the
-i flag, and to convert it to a video called my-animation.mp4.
The libx264 encoder only works with files that have even dimensions, like 320px by 240px. If the input GIF has odd dimensions you can include a crop filter to avoid FFmpeg throwing a 'height/width not divisible by 2' error:
ffmpeg -i my-animation.gif -vf "crop=trunc(iw/2)*2:trunc(ih/2)*2" -b:v 0 -crf 25 -f mp4 -vcodec libx264 -pix_fmt yuv420p my-animation.mp4
Create WebM videos
While MP4 has been around since 1999, WebM is a relatively new file format initially released in 2010. WebM videos are much smaller than MP4 videos, but not all browsers support WebM so it makes sense to generate both.
To use FFmpeg to convert my-animation.gif to a WebM video, run the following
command in your console:
ffmpeg -i my-animation.gif -c vp9 -b:v 0 -crf 41 my-animation.webm
Compare the difference
The cost savings between a GIF and a video can be pretty significant.
In this example, the initial GIF is 3.7 MB, compared to the MP4 version, which is 551 KB, and the WebM version, which is only 341 KB!
Replace the GIF img with a video
Animated GIFs have three key traits that a video needs to replicate:
- They play automatically.
- They loop continuously (usually, but it is possible to prevent looping).
- They're silent.
Luckily, you can recreate these behaviors using the <video> element.
<video autoplay loop muted playsinline></video>
A <video> element with these attributes plays automatically, loops endlessly,
plays no audio, and plays inline (that is, not full screen), all the hallmark
behaviors expected of animated GIFs! 🎉
Finally, the <video> element requires one or more <source> child elements
pointing to different video files that the browser can choose from, depending on
the browser's format support. Provide both WebM and MP4, so that if a browser
doesn't support WebM, it can fall back to MP4.
<video autoplay loop muted playsinline>
<source src="my-animation.webm" type="video/webm">
<source src="my-animation.mp4" type="video/mp4">
</video>
Effect on Largest Contentful Paint (LCP)
It should be noted that while <img> elements are candidates for LCP, <video> elements without a poster image are not LCP candidates. The solution in the case of emulating animated GIFs is not to add poster attribute to your <video> elements, because that image will go unused.
What does this mean for your website? The recommendation is to stick with using a <video> instead of an animated GIF, but with the understanding that such media will not be a candidate for LCP, and the next largest candidate will be used instead. As GIFs and <video>s are typically larger and so slower to download, moving to a different LCP candidate will likely even improve the site's LCP.