fix debian??

externals/ffmpeg/CMakeLists.txt

@@ -83,18 +83,20 @@ elseif (UNIX)
                     X11
                     "${CMAKE_SYSROOT}/usr/lib/xorg/amd64/libdrm.so")
             else()
-                pkg_check_modules(LIBDRM libdrm REQUIRED)
-                list(APPEND FFmpeg_HWACCEL_LIBRARIES
-                    ${LIBDRM_LIBRARIES})
-                list(APPEND FFmpeg_HWACCEL_INCLUDE_DIRS
-                    ${LIBDRM_INCLUDE_DIRS})
+                pkg_check_modules(LIBDRM libdrm)
+                if (LIBDRM_FOUND)
+                    list(APPEND FFmpeg_HWACCEL_LIBRARIES
+                        ${LIBDRM_LIBRARIES})
+                    list(APPEND FFmpeg_HWACCEL_INCLUDE_DIRS
+                        ${LIBDRM_INCLUDE_DIRS})
+                endif()
             endif()
             list(APPEND FFmpeg_HWACCEL_FLAGS
                 --enable-libdrm)
         endif()
         if(LIBVA_FOUND)
-            pkg_check_modules(LIBVA-DRM libva-drm REQUIRED)
-            pkg_check_modules(LIBVA-X11 libva-x11 REQUIRED)
+            pkg_check_modules(LIBVA-DRM libva-drm)
+            pkg_check_modules(LIBVA-X11 libva-x11)
             list(APPEND FFmpeg_HWACCEL_LIBRARIES
                 ${LIBVA-DRM_LIBRARIES}
                 ${LIBVA-X11_LIBRARIES}