Add support for v4l2loopback

It allows to send the video stream to /dev/videoN, so that it can be
captured (like a webcam) by any v4l2-capable tool.

PR #2232 <https://github.com/Genymobile/scrcpy/pull/2232>
PR #2233 <https://github.com/Genymobile/scrcpy/pull/2233>
PR #2268 <https://github.com/Genymobile/scrcpy/pull/2268>

Co-authored-by: Romain Vimont <rom@rom1v.com>

app/meson.build

@@ -33,6 +33,11 @@ else
     src += [ 'src/sys/unix/process.c' ]
 endif
 
+v4l2_support = host_machine.system() == 'linux'
+if v4l2_support
+    src += [ 'src/v4l2_sink.c' ]
+endif
+
 check_functions = [
     'strdup'
 ]
@@ -49,6 +54,10 @@ if not get_option('crossbuild_windows')
         dependency('sdl2'),
     ]
 
+    if v4l2_support
+        dependencies += dependency('libavdevice')
+    endif
+
 else
 
     # cross-compile mingw32 build (from Linux to Windows)
@@ -124,6 +133,9 @@ conf.set('SERVER_DEBUGGER', get_option('server_debugger'))
 # select the debugger method ('old' for Android < 9, 'new' for Android >= 9)
 conf.set('SERVER_DEBUGGER_METHOD_NEW', get_option('server_debugger_method') == 'new')
 
+# enable V4L2 support (linux only)
+conf.set('HAVE_V4L2', v4l2_support)
+
 configure_file(configuration: conf, output: 'config.h')
 
 src_dir = include_directories('src')