Before this, a failed test would keep failing because the output file
is not cleaned up and subsequent runs would refuse to overwrite it.
define FATE_CBS_TEST
# (codec, test_name, sample_file, output_format)
FATE_CBS_$(1) += fate-cbs-$(1)-$(2)
-fate-cbs-$(1)-$(2): CMD = md5 -i $(TARGET_SAMPLES)/$(3) -c:v copy -bsf:v $(1)_metadata -f $(4)
+fate-cbs-$(1)-$(2): CMD = md5 -i $(TARGET_SAMPLES)/$(3) -c:v copy -y -bsf:v $(1)_metadata -f $(4)
endef
# H.264 read/write