Replace the Qt multimedia audio back-end on the Windows build.

Adds an external project (wasapi) to download a low-latency audio plugin for Qt, as a precompiled DLL.
Adds a post-build command to use this new plugin instead of the default Qt audio plugin.

cmake/externals/wasapi/CMakeLists.txt

@@ -0,0 +1,24 @@
+if (WIN32)
+
+    set(EXTERNAL_NAME wasapi)
+    string(TOUPPER ${EXTERNAL_NAME} EXTERNAL_NAME_UPPER)
+    
+    include(ExternalProject)
+    ExternalProject_Add(
+        ${EXTERNAL_NAME}
+        URL http://hifi-public.s3.amazonaws.com/dependencies/qtaudio_wasapi.zip
+        URL_MD5 11c8a7728d6eda7223df800e10b70723
+        CONFIGURE_COMMAND ""
+        BUILD_COMMAND ""
+        INSTALL_COMMAND ""
+        LOG_DOWNLOAD 1
+    )
+    
+    # Hide this external target (for ide users)
+    set_target_properties(${EXTERNAL_NAME} PROPERTIES FOLDER "hidden/externals")
+    
+    ExternalProject_Get_Property(${EXTERNAL_NAME} SOURCE_DIR)
+    
+    set(${EXTERNAL_NAME_UPPER}_DLL_PATH ${SOURCE_DIR} CACHE FILEPATH "Location of wasapi DLL")
+
+endif()

cmake/macros/PackageLibrariesForDeployment.cmake

@@ -41,5 +41,15 @@ macro(PACKAGE_LIBRARIES_FOR_DEPLOYMENT)
       POST_BUILD
       COMMAND CMD /C "SET PATH=%PATH%;${QT_DIR}/bin && ${WINDEPLOYQT_COMMAND} ${EXTRA_DEPLOY_OPTIONS} $<$<OR:$<CONFIG:Release>,$<CONFIG:MinSizeRel>,$<CONFIG:RelWithDebInfo>>:--release> $<TARGET_FILE:${TARGET_NAME}>"
     )
+
+    set(QTAUDIO_PATH $<TARGET_FILE_DIR:${TARGET_NAME}>/audio)
+
+    # if present, replace qtaudio_windows.dll with qtaudio_wasapi.dll 
+    add_custom_command(
+      TARGET ${TARGET_NAME}
+      POST_BUILD
+      COMMAND if exist ${QTAUDIO_PATH}/qtaudio_windows.dll ( ${CMAKE_COMMAND} -E remove ${QTAUDIO_PATH}/qtaudio_windows.dll && ${CMAKE_COMMAND} -E copy ${WASAPI_DLL_PATH}/qtaudio_wasapi.dll ${QTAUDIO_PATH} && ${CMAKE_COMMAND} -E copy ${WASAPI_DLL_PATH}/qtaudio_wasapi.pdb ${QTAUDIO_PATH} )
+    )
+
   endif ()
 endmacro()

interface/CMakeLists.txt

@@ -126,6 +126,7 @@ if (WIN32)
   add_dependency_external_projects(sdl2)
   add_dependency_external_projects(OpenVR)
   add_dependency_external_projects(neuron)
+  add_dependency_external_projects(wasapi)
 endif()
 
 # disable /OPT:REF and /OPT:ICF for the Debug builds