Support OpenH264

[metalefty]

The current implementation of H264 uses x264. However, it is not available on Fedora or RHEL-compatible distros for legal reasons. It is instead provided by OpenH264 with the OpenH264 package.

Cisco pays all royalty fees for the precompiled binaries. Thus, Cisco's OpenH264 binaries are free to use and probably the only option to provide H264 capable xrdp in EPEL repo. Fedora/RHEL-compatible distros are not ignorable platform so it would be very nice if xrdp can support both x264 and OpenH264 as H264 encoder.

• https://www.openh264.org/faq.html
• https://en.wikipedia.org/wiki/OpenH264

[jsorg71]

I think Nex had a working prototype using OpenH264. If I remember right, we just need to add a capture type to get I420 yuv data as OpenH264 does not support NV12.