Project of the Week: Kap

The Electron community is growing quickly, and people are creating powerful new apps and tools at an astounding rate. To celebrate this creative momentum and keep the community informed of some of these new projects, we've decided to start a weekly blog series featuring noteworthy Electron-related projects.


This post is the first in the series, and features Kap, an open-source screen recording app built by Wulkano, a geodistributed team of freelance designers and developers.

Kap Screencast

What is Kap?

Kap is an open-source screen recorder built primarily for designers and developers to easily capture their work. People use it to share animated prototypes, document bugs, create silly GIFs and everything in-between.

We've seen people of all ages and backgrounds use it in educational settings, screencasts, tutorials... the list goes on. Even to create production assets! We're completely blown away by how well received our little side project has been.

Why did you build it?

That's a very good question, it's not like there's a lack of screen recorders out there! We felt the alternatives were either too complex, too expensive or too limited. Nothing felt just right for our everyday needs. We also think it's great when the tools we use to do our work are open-source, that way everyone can help shape them. Building Kap ended up being just as much about what we didn't do. It's all in the details, an accumulation of small improvements that became the outline of a tool we wanted to use.

However, and maybe most importantly, Kap has become a place for us to leave our worries at the door and just have fun building something for ourselves and people like us. It's so important to create an environment where you get to just vent, try new thins and enjoy your craft. No requirements, no pressure, no expectations. Should designers and developers side project? Why, yes. Yes, they should.

Why did you choose to build Kap on Electron?

There were a number of reasons:

We think the future of apps are in the browser, but we're not quite there yet. Electron is an important step in the journey towards that future. It not only makes the apps themselves more accessible, but also the code they're built with. An interesting thought is imagining a future where the OS is a browser, and the tabs are essentially Electron apps.

Additionally, being primarily web developers, we're big fans of the isomorphic nature of JavaScript, in that you can run JS on the client, server, and now the desktop. With web tech (HTML, CSS and JS), many things are much simpler than native: Faster prototyping, less code, flexbox > auto-layout (macOS/iOS).

What are some challenges you've faced while building Kap?

Using the resources Electron has available to record the screen was the biggest challenge. They simply weren't performant enough to meet our requirements and would render the project a failure in our eyes. Though at no fault of Electron itself, there's still a gap between native development and building desktop apps with web tech.

We spent a lot of time trying to work around the poor performance of the getUserMedia API, an issue originating in Chromium. One of our main goals when we set out to make Kap was to build the entire app with web tech. After trying everything we could to get it working (the minimum requirement being 30 FPS on a Retina screen), we eventually had to find another solution.

I see some Swift code in the repo. What's that about?

Being forced to look for alternatives to getUserMedia, we started experimenting with ffmpeg. Besides being one of the best tools for audio and video conversion it has the functionality of recording the screen in almost any OS, and we were able to record crispy video meeting our minimum requirement of 30 FPS on a Retina screen. Problem? The performance was ":weary:", the CPU usage was going haywire. So we went back to the drawing board, discussed our options and realised that we had to make a compromise. That resulted in Aperture, our own screen recording library for macOS written in Swift.

In what areas should Electron be improved?

We all know that Electron apps can have a thing for using RAM, but again, that's really a Chromium thing. It's part of how it works and it really depends on what you're running, for example Kap and Hyper typically use less than 100MB of memory.

One of the biggest areas of improvement that we see is payload, particularly how Electron distributes Chromium. One idea would be to have a shared Electron core and make app installers check if it's already present on the system.

Creating cross-platform Electron apps could be a better experience. Right now there are too many inconsistencies, platform-specific APIs, and missing features between platforms, making your codebase littered with if-else statements. For example, vibrancy is only supported on macOS, the auto-updater works differently on macOS and Windows, and is not even supported on Linux. Transparency is a hit or miss on Linux, usually miss.

It should also be easier to call native system APIs. Electron comes with a very good set of APIs, but sometimes you need functionality it doesn't provide. Creating a native Node.js addon is an option, but it's painful to work with. Ideally Electron would ship with a good FFI API, like fastcall. This would have enabled us to write the Swift part in JavaScript instead.

What are your favorite things about Electron?

Our favorite thing is easily the fact that anyone with knowledge of creating for the web can build and contribute to multi-platform native experiences. Not to mention the ease and joy of developing on it, the excellent documentation and the thriving ecosystem.

From a front-end perspective, building Kap felt no different than building a simple website using browser APIs. Electron does a really great job of making app development similar (basically identical) to web development. So simple in fact that there was no need for frameworks or similar to help us, just clean and modular JS and CSS.

We are also huge fans of the team building it, their dedication and support, and the active and friendly community they maintain. Hugs to all of you!

What's coming next in Kap?

The next step for us is to review the app in preparation for our 2.0.0 milestone, which includes a React re-write in addition to support for plugins, allowing developers to extend the functionality of Kap! We invite everyone to follow to project and contribute on our GitHub repository. We're listening and want to hear from as many of you as possible, let us know how we can make Kap the best possible tool it can be for you!

What is Wulkano?

Wulkano is a design studio and digital collective, a team of remote technologists who love working together on both client gigs and our own projects. We're a distributed but tight knit group of people from different places and backgrounds, sharing knowledge, ideas, experiences, but most importantly silly GIFs and memes, in our virtual office (which happens to be the Electron based Slack!).

Any Electron tips that might be useful to other developers?

Take advantage of and get involved in the fantastic community, check out Awesome Electron, look at examples and make use of the great docs!

Have feedback on this post? Let @electronjs know on Twitter.

Need help or found a bug? Contact us.