FFmpeg also depend on ALSA

Library/TeamTalkLib/build/ffmpeg.cmake

@@ -12,6 +12,13 @@ if (FFMPEG_STATIC)
     ${TTLIBS_ROOT}/ffmpeg/lib/libswresample.a
     ${TTLIBS_ROOT}/ffmpeg/lib/libswscale.a
     ${TTLIBS_ROOT}/ffmpeg/lib/libavutil.a)
+
+  if ( ${CMAKE_SYSTEM_NAME} MATCHES "Linux" )
+    # Ubuntu: libasound2-dev
+    find_library(ASOUND_LIBRARY asound)
+    list (APPEND FFMPEG_LINK_FLAGS ${ASOUND_LIBRARY})
+  endif()
+
 else()
   # Ubuntu: libavcodec-dev libavdevice-dev libavfilter-dev libavformat-dev libavresample-dev libavutil-dev libswresample-dev libswscale-dev
 
@@ -33,7 +40,6 @@ endif()
 
 set (FFMPEG_COMPILE_FLAGS -D__STDC_CONSTANT_MACROS)
 
-
 if ( ${CMAKE_SYSTEM_NAME} MATCHES "Darwin" )
   find_library(COCOA_LIBRARY Cocoa)
   list (APPEND FFMPEG_LINK_FLAGS ${COCOA_LIBRARY})