tungstenite-rs VS libass

You can start by following tungstenite-rs client example. And since you are connecting to an tls enabled endpoint you should enable tls features. And according to your API's doc it requires you to send serialized json string for requesting message response and you can use serde ande serde_json for serialization. This is a complete example where a hardcode string request:

staticpi, is a websocket forwarding service. Basically, it enables one to keep a Raspberry pi, or any computer, “connected”, in order to send and receive messages to and from any client, without having to deal with a static IP address, open ports on your router, or similar. Built in Rust, using axum, which in turn uses tungestine-rs for the websocket connections, tokio, sqlx, redis-rs and others.

There is a client module and client examples. If using tokio, there is tokio-tungstenite on top, which has various client functions.

tungstenite: "Lightweight stream-based WebSocket implementation. It's formerly WS2, the 2nd implementation of WS. WS2 is the chemical formula of tungsten disulfide, the tungstenite mineral."

tungstenite-rs

If you just want to connect to an existing api, async-tungstenite has a connect function. It should work with wss. See some discussion of this issue here.

TIL there's a library called 'libass'

Not Rust but libass :D

Dunno ... I'm kinda glad these guys didn't call their SSA/ASS implementation "open"

I see libass gets talked about on Reddit often enough.

libass is similar. For example, in the header:

libass

Using softsub allows you to reduce server usage as you only needs to deploy one video and multiple subtitles, but implementing it is hard: you can use this portable renderer, but just because it compiles to multiple platforms it does mean it run well on those, it might crash in low-end devices (there is even a Crunchyroll episode that loads multiple fonts at the same time, place a lot of texts moving and crash my phone).