Use native float32 output

minimp3.go

@@ -2,6 +2,7 @@ package minimp3
 
 /*
 #define MINIMP3_IMPLEMENTATION
+#define MINIMP3_FLOAT_OUTPUT
 #include "minimp3.h"
 */
 import "C"
@@ -17,7 +18,8 @@ const maxSamplesPerFrame = 1152 * 2
 // Decoder decode the mp3 stream by minimp3
 type Decoder struct {
 	source               io.Reader
-	mp3, pcm             []byte
+	mp3                  []byte
+	pcm                  []float32
 	mp3Length, pcmLength int
 	lastError            error
 	decode               C.mp3dec_t
@@ -29,17 +31,17 @@ func NewDecoder(source io.Reader) *Decoder {
 	d := &Decoder{
 		source: source,
 		mp3:    make([]byte, 1024*16),
-		pcm:    make([]byte, maxSamplesPerFrame*C.sizeof_short),
+		pcm:    make([]float32, maxSamplesPerFrame),
 	}
 
 	C.mp3dec_init(&d.decode)
 	return d
 }
 
-// Read copies the decoded audio data from the internal buffer to p and returns the number of bytes copied.
+// Read copies the decoded audio data from the internal buffer to p and returns the number of items copied.
 // If the internal buffer is empty, then Read first tries to read mp3 data from the source and decode it.
 // If len(p) == 0, then Read will return zero bytes, but if the internal buffer is empty, then before that it will still try to decode one frame and fill the internal buffer.
-func (d *Decoder) Read(p []byte) (int, error) {
+func (d *Decoder) Read(p []float32) (int, error) {
 	for d.pcmLength == 0 {
 		// If possible, fill the mp3 buffer completely
 		for d.mp3Length < len(d.mp3) && d.lastError == nil {
@@ -58,14 +60,14 @@ func (d *Decoder) Read(p []byte) (int, error) {
 		}
 
 		d.mp3Length = copy(d.mp3, d.mp3[d.info.frame_bytes:d.mp3Length])
-		d.pcmLength = int(samples * d.info.channels * C.sizeof_short)
+		d.pcmLength = int(samples * d.info.channels * C.sizeof_float)
 	}
 
-	n := copy(p, d.pcm[:d.pcmLength])
+	n := copy(p, d.pcm[:d.pcmLength/C.sizeof_float])
 	// If there is any data left in the pcm buffer, then move it to the beginning of the buffer
-	copy(d.pcm, d.pcm[n:d.pcmLength])
-	d.pcmLength -= n
-	return n, nil
+	copy(d.pcm, d.pcm[n:d.pcmLength/C.sizeof_float])
+	d.pcmLength -= n * C.sizeof_float
+	return n / C.sizeof_float, nil
 }
 
 // Seek sets a new position for reading audio data.
@@ -80,7 +82,7 @@ func (d *Decoder) Seek(offset int64, whence int) (int64, error) {
 	}
 
 	mp3BytesPerMsec := int64(d.info.bitrate_kbps) / 8
-	pcmBytesPerMsec := int64(d.info.channels*C.sizeof_short*d.info.hz) / 1000
+	pcmBytesPerMsec := int64(d.info.channels*C.sizeof_float*d.info.hz) / 1000
 
 	if mp3BytesPerMsec == 0 || pcmBytesPerMsec == 0 {
 		// There is no information about audio data. Probably not a single frame has been decoded yet