FATE: add a test for amix audio filter.

tests/fate/filter.mak

+FATE_AMIX += fate-filter-amix-simple
+fate-filter-amix-simple: CMD = avconv -filter_complex amix -i $(SRC) -ss 3 -i $(SRC1) -f f32le -
+fate-filter-amix-simple: REF = $(SAMPLES)/filter/amix_simple.pcm
+
+FATE_AMIX += fate-filter-amix-first
+fate-filter-amix-first: CMD = avconv -filter_complex amix=duration=first -ss 4 -i $(SRC) -i $(SRC1) -f f32le -
+fate-filter-amix-first: REF = $(SAMPLES)/filter/amix_first.pcm
+
+FATE_AMIX += fate-filter-amix-transition
+fate-filter-amix-transition: tests/data/asynth-44100-2-3.wav
+fate-filter-amix-transition: SRC2 = $(TARGET_PATH)/tests/data/asynth-44100-2-3.wav
+fate-filter-amix-transition: CMD = avconv -filter_complex amix=inputs=3:dropout_transition=0.5 -i $(SRC) -ss 2 -i $(SRC1) -ss 4 -i $(SRC2) -f f32le -
+fate-filter-amix-transition: REF = $(SAMPLES)/filter/amix_transition.pcm
+
+$(FATE_AMIX): tests/data/asynth-44100-2.wav tests/data/asynth-44100-2-2.wav
+$(FATE_AMIX): SRC  = $(TARGET_PATH)/tests/data/asynth-44100-2.wav
+$(FATE_AMIX): SRC1 = $(TARGET_PATH)/tests/data/asynth-44100-2-2.wav
+$(FATE_AMIX): CMP  = oneoff
+
+FATE_FILTER += $(FATE_AMIX)
+FATE_SAMPLES_AVCONV += $(FATE_AMIX)
+
 FATE_ASYNCTS += fate-filter-asyncts
 fate-filter-asyncts: SRC = $(SAMPLES)/nellymoser/nellymoser-discont.flv
 fate-filter-asyncts: CMD = pcm -i $(SRC) -af asyncts