audio: wav: add Seek and Position

audio/wav/streamer.go

@@ -7,115 +7,142 @@ import (
 	"github.com/pkg/errors"
 )
 
+type ReadSeekCloser interface {
+	io.Reader
+	io.Seeker
+	io.Closer
+}
+
 type Streamer struct {
-	rc  io.ReadCloser
+	rsc ReadSeekCloser
 	h   header
 	pos int32
 	err error
 }
 
-func NewStreamer(rc io.ReadCloser) (*Streamer, error) {
+func NewStreamer(rsc ReadSeekCloser) (s *Streamer, err error) {
 	var (
-		d   Streamer
-		err error
+		d    Streamer
+		herr error
 	)
-	d.rc = rc
-	d.h, err = readHeader(rc)
-	if err != nil {
-		rc.Close()
-		return nil, errors.Wrap(err, "wav")
+	d.rsc = rsc
+	defer func() { // hacky way to always close rsc if an error occured
+		if err != nil {
+			d.rsc.Close()
+		}
+	}()
+	d.h, herr = readHeader(rsc)
+	if herr != nil {
+		return nil, errors.Wrap(herr, "wav")
 	}
 	if d.h.formatType != 1 {
-		rc.Close()
 		return nil, errors.New("wav: unsupported format type")
 	}
 	if d.h.numChans <= 0 {
-		rc.Close()
 		return nil, errors.New("wav: invalid number of channels (less than 1)")
 	}
 	if d.h.bitsPerSample != 8 && d.h.bitsPerSample != 16 {
-		rc.Close()
 		return nil, errors.New("wav: unsupported number of bits per sample, 8 or 16 are supported")
 	}
 	return &d, nil
 }
 
-func (d *Streamer) Err() error {
-	return d.err
+func (s *Streamer) Err() error {
+	return s.err
 }
 
-func (d *Streamer) Duration() time.Duration {
-	numBytes := time.Duration(d.h.dataSize)
-	perFrame := time.Duration(d.h.bytesPerFrame)
-	sampRate := time.Duration(d.h.sampleRate)
+func (s *Streamer) Duration() time.Duration {
+	numBytes := time.Duration(s.h.dataSize)
+	perFrame := time.Duration(s.h.bytesPerFrame)
+	sampRate := time.Duration(s.h.sampleRate)
 	return numBytes / perFrame * time.Second / sampRate
 }
 
-func (d *Streamer) Stream(samples [][2]float64) (n int, ok bool) {
-	if d.pos >= d.h.dataSize {
+func (s *Streamer) Position() time.Duration {
+	frameIndex := time.Duration(s.pos / int32(s.h.bytesPerFrame))
+	frameTime := time.Second / time.Duration(s.h.sampleRate)
+	return frameIndex * frameTime
+}
+
+func (s *Streamer) Seek(d time.Duration) {
+	if d < 0 || s.Duration() < d {
+		panic("wav: seek duration out of range")
+	}
+	frame := int32(d / (time.Second / time.Duration(s.h.sampleRate)))
+	pos := frame * int32(s.h.bytesPerFrame)
+	_, err := s.rsc.Seek(int64(pos), io.SeekStart)
+	if err != nil {
+		s.err = err
+		return
+	}
+	s.pos = pos
+}
+
+func (s *Streamer) Stream(samples [][2]float64) (n int, ok bool) {
+	if s.pos >= s.h.dataSize {
 		return 0, false
 	}
 	switch {
-	case d.h.bitsPerSample == 8 && d.h.numChans == 1:
+	case s.h.bitsPerSample == 8 && s.h.numChans == 1:
 		width := 1
 		p := make([]byte, len(samples)*width)
-		n, err := d.rc.Read(p)
+		n, err := s.rsc.Read(p)
 		for i, j := 0, 0; i < n-width; i, j = i+width, j+1 {
 			val := float64(p[i])/(1<<8-1)*2 - 1
 			samples[j][0] = val
 			samples[j][1] = val
 		}
 		if err != nil {
-			d.err = err
+			s.err = err
 		}
-		d.pos += int32(n)
+		s.pos += int32(n)
 		return n / width, true
-	case d.h.bitsPerSample == 8 && d.h.numChans >= 2:
-		width := int(d.h.numChans)
+	case s.h.bitsPerSample == 8 && s.h.numChans >= 2:
+		width := int(s.h.numChans)
 		p := make([]byte, len(samples)*width)
-		n, err := d.rc.Read(p)
+		n, err := s.rsc.Read(p)
 		for i, j := 0, 0; i < n-width; i, j = i+width, j+1 {
 			samples[j][0] = float64(p[i+0])/(1<<8-1)*2 - 1
 			samples[j][1] = float64(p[i+1])/(1<<8-1)*2 - 1
 		}
 		if err != nil {
-			d.err = err
+			s.err = err
 		}
-		d.pos += int32(n)
+		s.pos += int32(n)
 		return n / width, true
-	case d.h.bitsPerSample == 16 && d.h.numChans == 1:
+	case s.h.bitsPerSample == 16 && s.h.numChans == 1:
 		width := 2
 		p := make([]byte, len(samples)*width)
-		n, err := d.rc.Read(p)
+		n, err := s.rsc.Read(p)
 		for i, j := 0, 0; i < n-width; i, j = i+width, j+1 {
 			val := float64(int16(p[i+0])+int16(p[i+1])*(1<<8)) / (1<<15 - 1)
 			samples[j][0] = val
 			samples[j][1] = val
 		}
 		if err != nil {
-			d.err = err
+			s.err = err
 		}
-		d.pos += int32(n)
+		s.pos += int32(n)
 		return n / width, true
-	case d.h.bitsPerSample == 16 && d.h.numChans >= 2:
-		width := int(d.h.numChans) * 2
+	case s.h.bitsPerSample == 16 && s.h.numChans >= 2:
+		width := int(s.h.numChans) * 2
 		p := make([]byte, len(samples)*width)
-		n, err := d.rc.Read(p)
+		n, err := s.rsc.Read(p)
 		for i, j := 0, 0; i <= n-width; i, j = i+width, j+1 {
 			samples[j][0] = float64(int16(p[i+0])+int16(p[i+1])*(1<<8)) / (1<<15 - 1)
 			samples[j][1] = float64(int16(p[i+2])+int16(p[i+3])*(1<<8)) / (1<<15 - 1)
 		}
 		if err != nil {
-			d.err = err
+			s.err = err
 		}
-		d.pos += int32(n)
+		s.pos += int32(n)
 		return n / width, true
 	}
 	panic("unreachable")
 }
 
-func (d *Streamer) Close() error {
-	err := d.rc.Close()
+func (s *Streamer) Close() error {
+	err := s.rsc.Close()
 	if err != nil {
 		return errors.Wrap(err, "wav")
 	}