Update RtAudio to v5.20 (#927)

external/rtaudio/README.md

@@ -1,10 +1,10 @@
 # RtAudio
 
-[![Build Status](https://travis-ci.org/thestk/rtaudio.svg?branch=master)](https://travis-ci.org/thestk/rtaudio)
+![Build Status](https://github.com/thestk/rtaudio/actions/workflows/ci.yml/badge.svg)
 
 A set of C++ classes that provide a common API for realtime audio input/output across Linux (native ALSA, JACK, PulseAudio and OSS), Macintosh OS X (CoreAudio and JACK), and Windows (DirectSound, ASIO and WASAPI) operating systems.
 
-By Gary P. Scavone, 2001-2019 (and many other developers!)
+By Gary P. Scavone, 2001-2021 (and many other developers!)
 
 This distribution of RtAudio contains the following:
 
@@ -28,38 +28,35 @@ RtAudio is a set of C++ classes that provides a common API (Application Programm
 
 RtAudio incorporates the concept of audio streams, which represent audio output (playback) and/or input (recording).  Available audio devices and their capabilities can be enumerated and then specified when opening a stream.  Where applicable, multiple API support can be compiled and a particular API specified when creating an RtAudio instance.  See the \ref apinotes section for information specific to each of the supported audio APIs.
 
+## Building
+
+Several build systems are available.  These are:
+
+  - autotools (`./autogen.sh; make` from git, or `./configure; make` from tarball release)
+  - CMake (`mkdir build; cd build; ../cmake; make`)
+  - meson (`meson build; cd build; ninja`)
+
+See `install.txt` for more instructions about how to select the audio backend API.  By
+default all detected APIs will be enabled.
+
+We recommend using the autotools-based build for packaging purposes.  Please note that
+RtAudio is designed as a single `.cpp` and `.h` file so that it is easy to copy directly
+into a project.  In that case you need to define the appropriate flags for the desired
+backend APIs.
+
+## FAQ
+
+### Why does audio only come to one ear when I choose 1-channel output?
+
+RtAudio doesn't automatically turn 1-channel output into stereo output with copied values
+to each channel, it really only opens one channel.  So, if this is the behaviour you want,
+you have to do this copying in your audio stream callback.
+
 ## Further Reading
 
 For complete documentation on RtAudio, see the doc directory of the distribution or surf to http://www.music.mcgill.ca/~gary/rtaudio/.
 
 
 ## Legal and ethical:
 
-The RtAudio license is similar to the MIT License.
-
-    RtAudio: a set of realtime audio i/o C++ classes
-    Copyright (c) 2001-2019 Gary P. Scavone
-
-    Permission is hereby granted, free of charge, to any person
-    obtaining a copy of this software and associated documentation files
-    (the "Software"), to deal in the Software without restriction,
-    including without limitation the rights to use, copy, modify, merge,
-    publish, distribute, sublicense, and/or sell copies of the Software,
-    and to permit persons to whom the Software is furnished to do so,
-    subject to the following conditions:
-
-    The above copyright notice and this permission notice shall be
-    included in all copies or substantial portions of the Software.
-
-    Any person wishing to distribute modifications to the Software is
-    asked to send the modifications to the original developer so that
-    they can be incorporated into the canonical version.  This is,
-    however, not a binding provision of this license.
-
-    THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
-    EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
-    MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT.
-    IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR
-    ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF
-    CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION
-    WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
+The RtAudio license is similar to the MIT License.  Please see [LICENSE](LICENSE).