diff --git a/revid/inputs.go b/revid/inputs.go
index c1576019..66706e03 100644
--- a/revid/inputs.go
+++ b/revid/inputs.go
@@ -53,6 +53,13 @@ const (
 	ipCamPass = "admin"
 )
 
+type AVDevice interface {
+	io.Reader
+	Start() error
+	Stop() error
+	Set() error
+}
+
 // startRaspivid sets up things for input from raspivid i.e. starts
 // a raspivid process and pipes it's data output.
 func (r *Revid) startRaspivid() (func() error, error) {