mp4parse-rust

The mp4 demuxer is indeed in Rust [0], and runs in the content process (= the process in which the web page is loaded). We don't have a h264 decoder in our source tree, we use the platform's decoder (because of patents). It's very often in a separate, dedicated process, and when it's not, it's in the GPU process, because when hardware accelerated decoders are used, they're using more or less the same resources as the rendering code. Those other processes with the tightest sandbox possible (per process type, per platform, etc.), and don't have access to the web page. On Linux, the platform decoder we're using is `libavcodec` from FFmpeg, but that's still in a separate process with a tight sandbox. We're also doing something interesting, which is compiling libraries to WASM and then back to native code to get memory safety [1]. This is used