TLDR; all the video rendering happens on your own machine. So not really helpful if you have cheap hardware.
Mastershot is an online video editor. I am not promoting the use web app either. That is entirely up to you. This post isn't a critique about the experience the app lends to end-users. I myself haven't used the app so far. It requires a signup and everything. So I never bothered. Its completely browser-based, and, that is the actual problem.
So a bit of history: I was interested in a web-based video editor. I have frozen/crashed my machine a couple times trying to edit videos, and, then render them. I frequently run into these troubles since I use a computer with inferior hardware. I am still on the lookout for a solution however. I want it to be opensource and something I can setup on my own, and, run in my own home network.
So a cursory internet search lead me to Mastershot. I understand that it is a web-based video editor. (Or precisely a chrome-based video editor - chromium or google chrome). The author markets it as a "simple" editor where the video you upload, never leaves the browser. Further, he contrasts with other services (for e.g. like WeVideo) where they force you to bear concerned company's watermark logo on the video or something to this effect; his app does not indulge in such branding tactics.
You can pause here and check out the app, or the hackernews comments about this app, and try to understand the app. It is cool to witness how much browser technology has evolved - today we are able to do video editing in the web browser. I was mesmerized until I realized where I was coming from...
A critical experience related to video editing is the final thing - the video rendering. After all the hard work of editing, mixing audio, adding images/text/etc, you want to distribute the video in a format that your audience can play. Not many people realize that this is also a critical experience. You can term it as the post-editing experience for lack of a better word.
After getting your resolution, file formats, etc all correct, you have to wait for the final video to "render". And this is CPU intensive. Which was why, for long videos, my pc (with inferior hardware) always gave up responding to even a mouse moving across the screen. Mouse movements became sluggish.
So it finally means, for faster rendering, you need a pc with some superior hardware. It will definitely burn your pockets. You can buy laptops which have the processing power to do this. But, I just don't feel comfortable being "mobile" with an expensive piece of hardware. I rather invest in a low end laptop, and, offset all the rendering to a much powerful machine...like a dedicated server. There is also a privacy aspect to this hypothetical web-based solution I am hoping to obtain. But its completely for personal use inside of my personal network. So privacy isn't so much significant here.
Thus, the reason for why I started off writing this post. I realize that Mastershot is a clever app, but it does not help with rendering because it all happens in your browser on your machine which utilizes your own hardware for rendering. So if your hardware is not up to it, your computer mouse movements while rendering might be erratic.
