README.md: minor cleanups

I don't think MPlayer/mplayer2 and Libav are well-known enough anymore
to warrant such a prominent place in the top-level README file of this
project. It's just useless noise to most users. So I've moved these
things to the FAQ.

Update some other minor things.

README.md

@@ -9,12 +9,9 @@
 * [Downloads](#downloads)
 * [Changelog](#changelog)
 * [Compilation](#compilation)
-* [FFmpeg vs. Libav](#ffmpeg-vs-libav)
-* [FFmpeg ABI compatibility](#ffmpeg-abi-compatibility)
 * [Release cycle](#release-cycle)
 * [Bug reports](#bug-reports)
 * [Contributing](#contributing)
-* [Relation to MPlayer and mplayer2](#relation-to-mplayer-and-mplayer2)
 * [License](#license)
 * [Contact](#contact)
 
@@ -114,7 +111,7 @@ Essential dependencies (incomplete list):
 - Lua (optional, required for the OSC pseudo-GUI and youtube-dl integration)
 - libjpeg (optional, used for screenshots only)
 - uchardet (optional, for subtitle charset detection)
-- vdpau and vaapi libraries for hardware decoding on Linux (optional)
+- nvdec and vaapi libraries for hardware decoding on Linux (optional)
 
 Libass dependencies:
 
@@ -131,10 +128,10 @@ FFmpeg dependencies:
 - libx264/libmp3lame/libfdk-aac if you want to use encoding (have to be
   explicitly enabled when compiling FFmpeg)
 - For native DASH playback, FFmpeg needs to be built with --enable-libxml2
-  (although there are security implications).
+  (although there are security implications, and DAHS support has lots of bugs).
+- AV1 decoding support requires dav1d.
 - For good nvidia support on Linux, make sure nv-codec-headers is installed
   and can be found by configure.
-- Libav support is broken. (See section below.)
 
 Most of the above libraries are available in suitable versions on normal
 Linux distributions. For ease of compiling the latest git master of everything,
@@ -147,28 +144,6 @@ or cross-compile from Linux with MinGW. See
 [Windows compilation][windows_compilation].
 
 
-## FFmpeg vs. Libav
-
-
-Generally, mpv should work with the latest release as well as the git version
-of FFmpeg. Libav support is currently broken, because they did not add certain
-FFmpeg API changes which mpv relies on.
-
-
-## FFmpeg ABI compatibility
-
-mpv does not support linking against FFmpeg versions it was not built with, even
-if the linked version is supposedly ABI-compatible with the version it was
-compiled against. Expect malfunctions, crashes, and security issues if you
-do it anyway.
-
-The reason for not supporting this is because it creates far too much complexity
-with little to no benefit, coupled with absurd and unusable FFmpeg API
-artifacts.
-
-Newer mpv versions will refuse to start if runtime and compile time FFmpeg
-library versions mismatch.
-
 ## Release cycle
 
 Every other month, an arbitrary git snapshot is made, and is assigned
@@ -205,16 +180,6 @@ You can check [the wiki](https://github.com/mpv-player/mpv/wiki/Stuff-to-do)
 or the [issue tracker](https://github.com/mpv-player/mpv/issues?q=is%3Aopen+is%3Aissue+label%3A%22feature+request%22)
 for ideas on what you could contribute with.
 
-## Relation to MPlayer and mplayer2
-
-mpv is a fork of MPlayer. Much has changed, and in general, mpv should be
-considered a completely new program, rather than a MPlayer drop-in replacement.
-
-For details see [FAQ entry](https://github.com/mpv-player/mpv/wiki/FAQ#How_is_mpv_related_to_MPlayer).
-
-If you are wondering what's different from mplayer2 and MPlayer, an incomplete
-and largely unmaintained list of changes is located [here][mplayer-changes].
-
 ## License
 
 GPLv2 "or later" by default, LGPLv2.1 "or later" with `--enable-lgpl`.
@@ -233,10 +198,8 @@ Most activity happens on the IRC channel and the github issue tracker.
 [releases]: https://github.com/mpv-player/mpv/releases
 [mpv-build]: https://github.com/mpv-player/mpv-build
 [issue-tracker]:  https://github.com/mpv-player/mpv/issues
-[ffmpeg_vs_libav]: https://github.com/mpv-player/mpv/wiki/FFmpeg-versus-Libav
 [release-policy]: https://github.com/mpv-player/mpv/blob/master/DOCS/release-policy.md
 [windows_compilation]: https://github.com/mpv-player/mpv/blob/master/DOCS/compile-windows.md
-[mplayer-changes]: https://github.com/mpv-player/mpv/blob/master/DOCS/mplayer-changes.rst
 [interface-changes]: https://github.com/mpv-player/mpv/blob/master/DOCS/interface-changes.rst
 [api-changes]: https://github.com/mpv-player/mpv/blob/master/DOCS/client-api-changes.rst
 [restore-old-bindings]: https://github.com/mpv-player/mpv/blob/master/etc/restore-old-bindings.conf