Broadcast grade color scopes, inside a LiveView

A few months ago we needed real video scopes inside our Phoenix app. Not toy histograms. The actual four you see in DaVinci Resolve, Baselight, Nuke: waveform, RGB parade, vectorscope, histogram. Colorists grade with these. If yours are off, people stop trusting the tool within about ten seconds.

I looked at the ticket and thought, “ok, this is where we finally bolt on a separate frontend”. Turns out no. A LiveView hook and about 900 lines of WebGL later, the scopes were running at 30 fps next to the grading controls, and the Elixir side was basically asleep.

At CyanView, we run a Phoenix LiveView application on embedded hardware. Out of the box, the BEAM VM was eating 300MB of RAM at idle and keeping the CPU at 45%. After tuning, we got it down to ~120MB and 5-10% idle CPU.

Here’s exactly what we changed and why each thing matters.

If you’re running a Phoenix LiveView application and your iOS Safari users are experiencing frozen pages, slow reconnects, or 10+ second hangs after returning from sleep this article is for you.

I’ve been running a production Phoenix LiveView application. The app worked great on desktop, but iPhone users kept reporting the same thing: the page would freeze or hang for several seconds after switching back from another app or unlocking their phone. Sometimes the page would never recover at all.

We had two repos of Elixir, seventy-five LiveView components, five sheets of high-powered Phoenix channels, a saltshaker half-full of SQLite databases, and a whole multicolored collection of Burrito deployables, Tauri binaries, WebView wrappers, hot-reloaders… Also, a quart of WebSockets, a quart of GenServers, a case of Ecto queries, a pint of raw BEAM bytecode, and two dozen supervisors.

The only thing that really worried me was the WebView. There is nothing in the world more helpless and irresponsible and depraved than a developer in the depths of a cross-platform binge, and I knew we’d get into that rotten stuff pretty soon.

Livebook is very powerful application which can be used in many different ways with your Phoneix project. I have few apps running on my VPS and sometimes I would like to run some functions without creating interface for them from admin side, such as cache clean up. Perhaps run some analytical queries to the database and much more.