Use libopus for decoding Audio

cmake/FindOpus.cmake

@@ -0,0 +1,38 @@
+if(Opus_INCLUDE_DIR AND Opus_LIBRARY)
+  set(Opus_FIND_QUIETLY TRUE)
+endif()
+
+
+find_path(Opus_INCLUDE_DIR opus.h
+          /usr/local/include
+          /usr/include
+)
+
+find_library(Opus_LIBRARY NAMES opus
+             PATHS /usr/local/lib /usr/lib)
+
+find_library(Celt_LIBRARY NAMES celt
+             PATHS /usr/local/lib /usr/lib)
+
+find_library(Silk_LIBRARY NAMES silk_common
+             PATHS /usr/local/lib /usr/lib)
+
+set(Opus_LIBRARIES
+    ${Opus_LIBRARY}
+    ${Celt_LIBRARY}
+    ${Silk_LIBRARY})
+
+
+if(Opus_INCLUDE_DIR AND Opus_LIBRARY)
+  set(Opus_FOUND TRUE)
+endif()
+
+if (Opus_FOUND)
+    if(NOT Opus_FIND_QUIETLY)
+        message(STATUS "Found libopus: ${Opus_INCLUDE_DIR}")
+    endif()
+else()
+    if(Opus_FIND_REQUIRED)
+        message(FATAL_ERROR "Could not find libopus")
+    endif()
+endif()