Added list devices option

main.go

@@ -5,6 +5,7 @@ import (
 	"log"
 	"os"
 	"os/signal"
+	"strconv"
 	"strings"
 	"syscall"
 
@@ -13,20 +14,34 @@ import (
 )
 
 func main() {
-	if len(os.Args) == 0 {
-		log.Fatal("Missing file or playlist argument.")
+	if len(os.Args[1]) == 2 && os.Args[1] == "-l" {
+		err := midiplayer.ListDevices()
+		if err != nil {
+			log.Fatal(err)
+		}
+
+		return
 	}
 
-	p, err := midiplayer.NewPlayer()
+	if len(os.Args) != 3 {
+		log.Fatal("Missing DeviceID and file or playlist argument.")
+	}
+
+	deviceID, err := strconv.Atoi(os.Args[1])
 	if err != nil {
-		log.Fatal(err)
+		panic(err)
+	}
+
+	p, err := midiplayer.NewPlayer(int64(deviceID))
+	if err != nil {
+		log.Fatal("Invalid deviceID. ")
 	}
 	defer p.Close()
 
 	registerInterrupSignal(p)
 
-	if strings.HasSuffix(strings.ToLower(os.Args[1]), ".mid") {
-		midi, err := midiparser.ParseMidiFile(os.Args[1])
+	if strings.HasSuffix(strings.ToLower(os.Args[2]), ".mid") {
+		midi, err := midiparser.ParseMidiFile(os.Args[2])
 		if err != nil {
 			log.Fatal(err)
 		}
@@ -35,7 +50,7 @@ func main() {
 		return
 	}
 
-	err = playPlaylist(os.Args[1], p)
+	err = playPlaylist(os.Args[2], p)
 	if err != nil {
 		log.Fatal(err)
 	}

midiplayer/player.go

@@ -18,9 +18,9 @@ type Player struct {
 }
 
 // NewPlayer returns an instance of a Player
-func NewPlayer() (*Player, error) {
+func NewPlayer(deviceID int64) (*Player, error) {
 	portmidi.Initialize()
-	out, err := portmidi.NewOutputStream(2, 1024, 0)
+	out, err := portmidi.NewOutputStream(portmidi.DeviceID(deviceID), 1024, 0)
 	if err != nil {
 		return nil, err
 	}
@@ -137,3 +137,26 @@ func muteAllNotes(out *portmidi.Stream) {
 		)
 	}
 }
+
+// ListDevices lists all the available output MIDI devices and their IDs
+func ListDevices() error {
+	err := portmidi.Initialize()
+	if err != nil {
+		return err
+	}
+
+	defer portmidi.Terminate()
+
+	numDevices := portmidi.CountDevices()
+
+	fmt.Println("Available output MIDI devices")
+	for i := 0; i < numDevices; i++ {
+		info := portmidi.Info(portmidi.DeviceID(i))
+
+		if info.IsOutputAvailable {
+			fmt.Println("ID:", i, "Name:", info.Name)
+		}
+	}
+
+	return nil
+}