diff --git a/src/output/MultipleOutputs.cxx b/src/output/MultipleOutputs.cxx
index 2791e7045..6cd2c9fa6 100644
--- a/src/output/MultipleOutputs.cxx
+++ b/src/output/MultipleOutputs.cxx
@@ -37,6 +37,7 @@
 
 MultipleOutputs::MultipleOutputs(MixerListener &_mixer_listener)
 	:mixer_listener(_mixer_listener),
+	 input_audio_format(AudioFormat::Undefined()),
 	 buffer(nullptr), pipe(nullptr),
 	 elapsed_time(-1)
 {