Sitting on Clouds is pretty good, especially for newer stuff.

You can either share your screen/window or upload a file. There’s probably a filesize limit, but I’m not sure what it is. I was using it to upload episodes of GameCenter CX to stream and I didn’t have any issues, but those episodes aren’t super huge. YMMV if you’re trying to upload a bluray rip or something.

I haven’t tried it on Linux, but a while back I was streaming stuff for my friends on Kosmi. It worked pretty well.