diff --git a/format/mp4/handler.go b/format/mp4/handler.go
index ce77dc9..aeef1cc 100644
--- a/format/mp4/handler.go
+++ b/format/mp4/handler.go
@@ -11,6 +11,14 @@ var CodecTypes = []av.CodecType{av.H264, av.AAC}
 func Handler(h *avutil.RegisterHandler) {
 	h.Ext = ".mp4"
 
+	h.Probe = func(b []byte) bool {
+		switch string(b[4:8]) {
+		case "moov","ftyp","free","mdat","moof":
+			return true
+		}
+		return false
+	}
+
 	h.ReaderDemuxer = func(r io.Reader) av.Demuxer {
 		return NewDemuxer(r.(io.ReadSeeker))
 	}