Added utilities to fetch ALAC properties

mp4.go

@@ -213,6 +213,18 @@ func NewFormatDecoder(reader io.Reader) *FormatDecoder {
 	}
 }
 
+func (d *FormatDecoder) GetChannels() int {
+	return d.handle.GetChannels()
+}
+
+func (d *FormatDecoder) GetBitDepth() int {
+	return d.handle.GetBitDepth()
+}
+
+func (d *FormatDecoder) GetSampleRate() int {
+	return d.handle.GetSampleRate()
+}
+
 func (d *FormatDecoder) Read() (buf []byte) {
 	if d.currentSegment >= len(d.parsedMp4.Segments) {
 		//EOF