Basic Build Instructions for Shotcut

We will not be able to cover everything here, and you are largely on your
own, but here are some hints. There is a big build bash script that is used
to make Shotcuts daily builds. It is the authoritative install reference:
  src/shotcut/scripts/build-shotcut.sh

We cannot cover how to build all of Shotcut's dependencies from scratch here.
On Linux, we rely upon Ubuntu's packages to provide most of the
more mundane dependencies. The rest like x264, x265, libvpx, lame, libopus,
FFmpeg, and frei0r are provided by the script.

For macOS, we rely upon macports to provide the dependencies:
  port install ffmpeg libsamplerate libsdl2 sox glib2 jack

For Windows, see this page on the MLT wiki about getting pre-built
dependencies from various sources on the Internet:
  https://www.mltframework.org/docs/windowsbuild/
Except, now we build FFmpeg instead of using a pre-built copy.

As for Shotcut itself, its really as simple as:
  mkdir build ; cd build ; qmake .. ; make

Then, there is the app bundling so that dependencies can be located and Qt
plugins included. For that you really need to see the build script; it
is fairly complicated especially on macOS. On Linux, we just use a
common install prefix and the build script generates shell scripts to
establish a redirected environment. On Windows, everything is relative
to the directory containing the .exe. DLLs are in the same directory as
the .exe, and the lib and share folders are sub-directories. On macOS, all
dependencies need to be put into the correct locations in Shotcut.app,
and the build script modifies all dylibs to pull them in and make their
inter-dependencies relative to the executable. If you are just building for
yourself, you do not need to do that. You can just let Shotcut use
the macports dependencies in /opt/local.
