I need to create an app that can record video using a webcam or mobile camera (it needs to be cross platform).
So far I have written a small proof of concept using webrt
The only cross platform web video recorder is the HDFVR webcam video recorder software.
It uses Flash (records using Flash codecs + streams to a media server) on the desktop and the HTML Media Capture API (record using OS + upload to webserver) on mobile to record video from pretty much any desktop or mobile browser.
You can link it to a ffmpeg installation to convert everything to a cross platform format like MP4 (iOS records to a .mov container that doesn't play on Android) and it also has a JS API.