Highlights:
- amrparse, aacparse, ac3parse, flacparse, mpegaudioparse, dcaparse audio parsers (moved from -bad)
- muxers now mux based on running time
- ISO MP4 muxers: mp4mux/3gppmux/qtmux/mj2mux (moved from -bad)
- new matroskaparse element
- new v4l2radio element
- rtpsession: support RTCP Early Feedback (the AVPF profile)
- orc 0.4.14 or newer recommended
- many other fixes and improvements
"Low" etc. are quality settings here (e.g. for the internal resampler).
Some day when we use GLib's i18n functions we might want to use
NC_() and g_dpgettext2() here instead of the comments.
Fixes#555967.