setup/destination: channels

lib/setup/setupDestination

@@ -334,11 +334,25 @@ setupDestination() {
 	done
 	unset copiedmimes
 	cat <<-EODesc
+
+        Channels (integer):
+            Produced files should have this many channels, no more, no less.
 	EODesc
+	expr='^[0-9]*$'
 	comeagain() {
-		:
+		read							\
+			-e						\
+			${destinationchannels["$destination"]+-i${destinationchannels["$destination"]}}\
+			-p'Channel count: '				\
+			value
+		if ! [[ $value =~ $expr ]]
+		then
+			echo "Invalid channel count: $value" >&2
+			comeagain
+		fi
 	}
 	comeagain
+	destinationchannels["$destination"]=$value
 	cat <<-EODesc
 	EODesc
 	comeagain() {