examples: add recording-audio example

Signed-off-by: Lilis Iskandar <lilis@veand.co>

examples/recording-audio/recording-audio.go

@@ -0,0 +1,89 @@
+package main
+
+/*
+typedef unsigned char Uint8;
+void OnAudio(void *userdata, Uint8 *stream, int length);
+*/
+import "C"
+import (
+	"log"
+	"os"
+	"os/signal"
+	"reflect"
+	"syscall"
+	"unsafe"
+
+	"github.com/veandco/go-sdl2/sdl"
+)
+
+const (
+	DefaultFrequency = 16000
+	DefaultFormat    = sdl.AUDIO_S16
+	DefaultChannels  = 1
+	DefaultSamples   = 512
+)
+
+var (
+	audioC = make(chan []int16, 1)
+)
+
+//export OnAudio
+func OnAudio(userdata unsafe.Pointer, _stream *C.Uint8, _length C.int) {
+	// We need to cast the stream from C uint8 array into Go int16 slice
+	length := int(_length) / 2                                                                      // Divide by 2 because a single int16 consists of two uint8
+	header := reflect.SliceHeader{Data: uintptr(unsafe.Pointer(_stream)), Len: length, Cap: length} // Build the slice header for our int16 slice
+	buf := *(*[]int16)(unsafe.Pointer(&header))                                                     // Use the slice header as int16 slice
+
+	// Copy the audio samples into temporary buffer
+	audioSamples := make([]int16, length)
+	copy(audioSamples, buf)
+
+	// Send the temporary buffer to our main function via our Go channel
+	audioC <- audioSamples
+}
+
+func main() {
+	var dev sdl.AudioDeviceID
+	var err error
+
+	// Initialize SDL2
+	if err = sdl.Init(sdl.INIT_AUDIO); err != nil {
+		log.Fatal(err)
+	}
+	defer sdl.Quit()
+
+	// Specify the configuration for our default recording device
+	spec := sdl.AudioSpec{
+		Freq:     DefaultFrequency,
+		Format:   DefaultFormat,
+		Channels: DefaultChannels,
+		Samples:  DefaultSamples,
+		Callback: sdl.AudioCallback(C.OnAudio),
+	}
+
+	// Open default recording device
+	defaultRecordingDeviceName := sdl.GetAudioDeviceName(0, true)
+	if dev, err = sdl.OpenAudioDevice(defaultRecordingDeviceName, true, &spec, nil, 0); err != nil {
+		log.Fatal(err)
+	}
+	defer sdl.CloseAudioDevice(dev)
+
+	// Start recording audio
+	sdl.PauseAudioDevice(dev, false)
+
+	// Listen to OS signals
+	c := make(chan os.Signal, 1)
+	signal.Notify(c, os.Interrupt, syscall.SIGTERM)
+
+	// Run infinite loop until we receive SIGINT or SIGTERM!
+	running := true
+	for running {
+		select {
+		case sig := <-c:
+			log.Printf("Received signal %v. Exiting.\n", sig)
+			running = false
+		case audioSamples := <-audioC:
+			log.Printf("Got %d audio samples!\n", len(audioSamples))
+		}
+	}
+}