Support GPU encode

[nitedani]

Gstreamer has built-in support for various GPU accelerated encoders. There could be multiple gstreamer pipelines pre-defined in the egress code(x264enc, nvh264enc, openh264enc, vp8enc, ...) and then selected using the egress configuration/ selected by auto-detecting the hardware. This would be very useful, a single machine could handle much more egress load and reduce operational costs.

[nitedani]

Is x264enc always faster than openh264enc and vp8enc? Have you experimented with how their configuration affects their speed?

[frostbyte73]

x264enc is much faster than vp8enc (we weren't able to run vp8enc in real time without hardware acceleration), but I have not tested against openh264enc. We have experimented a bit with configuration, and landed on speed-preset = veryfast