libfvad: voice activity detection (VAD) library

This is a fork of the VAD engine that is part of the WebRTC Native Code package
(https://webrtc.org/native-code/), for use as a standalone library independent
from the rest of the WebRTC code. There are currently no changes in
functionality.

Building and Installing

libfvad uses autoconf/automake and can be build and installed with the usual:

./configure
make
sudo make install

• When building from the cloned git repository (instead of a downloaded release),
  run autoreconf -i to create the missing configure script (this requires autoconf, libtool and pkg-config; e.g. run sudo apt install autoconf libtool pkg-config on Debian/Ubuntu first).
• An optional example can be enabled enabled by ./configure --enable-examples.
  This requires libsndfile (http://www.mega-nerd.com/libsndfile/, e.g.
  apt install libsndfile1-dev).

Usage

The API is documented in the include/fvad.h header file. See also
examples/fvadwav.h.

Development notes

Recommended CFLAGS to turn on warnings: -std=c11 -Wall -Wextra -Wpedantic.
Tests can be run with make check.

Origin

This library largely consists of parts of the WebRTC Native Code package, the
repository of which can be found at
https://chromium.googlesource.com/external/webrtc:

• Most of webrtc/common_audio/vad/ has been moved to src/vad.
• Parts of webrtc/common_audio/signal_processing have been moved to
  src/signal_processing. Parts of this signal processing library not needed
  by the VAD engine have been removed. Also, some platform-specific assembly
  code has been removed for now, for easier maintainability.
• Relevant unit tests have been converted into automake tests and moved to
  tests.

Merging upstream changes

It is intended that future changes and fixes in the WebRTC Native Code package
will also be be merged into libfvad.

To help with this, the libfvad git
repository has an upstream-import branch containing the required subset of the
WebRTC Native Code package's files, and an upstream-renamed branch which also
contains these unmodified files, but moved/renamed to the libfvad directory
structure.

The tools/import.sh script is intended to be run in the
upstream-import branch and imports changes from a local clone of the WebRTC
Native Code package git repository; it reads tools/import-paths which contains
the list of files to import, and reads and updates tools/import-commit which
contains the most recent imported commit hash of the source repository.

After this import, the changes can be merged first into the upstream-renamed
branch and then into the master branch. The intermediate step is necessary
because git merge would treat files that were both renamed and heavily changed
as new files.