audio/vorbis: add (*Stream).SampleRate

Updates #2996

audio/vorbis/vorbis.go

@@ -27,8 +27,9 @@ import (
 
 // Stream is a decoded audio stream.
 type Stream struct {
-	decoded io.ReadSeeker
-	size    int64
+	decoded    io.ReadSeeker
+	size       int64
+	sampleRate int
 }
 
 // Read is implementation of io.Reader's Read.
@@ -50,6 +51,11 @@ func (s *Stream) Length() int64 {
 	return s.size
 }
 
+// SampleRate returns the sample rate of the decoded stream.
+func (s *Stream) SampleRate() int {
+	return s.sampleRate
+}
+
 type decoder interface {
 	Read([]float32) (int, error)
 	SetPosition(int64) error
@@ -152,7 +158,7 @@ func decode(in io.Reader) (*decoded, int, int, error) {
 // A Stream doesn't close src even if src implements io.Closer.
 // Closing the source is src owner's responsibility.
 func DecodeWithoutResampling(src io.Reader) (*Stream, error) {
-	decoded, channelCount, _, err := decode(src)
+	decoded, channelCount, sampleRate, err := decode(src)
 	if err != nil {
 		return nil, err
 	}
@@ -166,8 +172,9 @@ func DecodeWithoutResampling(src io.Reader) (*Stream, error) {
 		size *= 2
 	}
 	stream := &Stream{
-		decoded: s,
-		size:    size,
+		decoded:    s,
+		size:       size,
+		sampleRate: sampleRate,
 	}
 	return stream, nil
 }
@@ -204,7 +211,11 @@ func DecodeWithSampleRate(sampleRate int, src io.Reader) (*Stream, error) {
 		s = r
 		size = r.Length()
 	}
-	stream := &Stream{decoded: s, size: size}
+	stream := &Stream{
+		decoded:    s,
+		size:       size,
+		sampleRate: sampleRate,
+	}
 	return stream, nil
 }
 

audio/vorbis/vorbis_test.go

@@ -50,16 +50,16 @@ func TestMono(t *testing.T) {
 	}
 
 	// Stream decoded by audio/vorbis.DecodeWithSampleRate() is always 16bit stereo.
-	got := s.Length()
-
 	// On the other hand, the original vorbis package is monoral.
 	// As Length() represents the number of samples,
 	// this needs to be doubled by 2 (= bytes in 16bits).
-	want := r.Length() * 2 * 2
-
-	if got != want {
+	if got, want := s.Length(), r.Length()*2*2; got != want {
 		t.Errorf("s.Length(): got: %d, want: %d", got, want)
 	}
+
+	if got, want := s.SampleRate(), audioContext.SampleRate(); got != want {
+		t.Errorf("s.SampleRate(): got: %d, want: %d", got, want)
+	}
 }
 
 func TestTooShort(t *testing.T) {
@@ -70,11 +70,13 @@ func TestTooShort(t *testing.T) {
 		t.Fatal(err)
 	}
 
-	got := s.Length()
-	want := int64(79424)
-	if got != want {
+	if got, want := s.Length(), int64(79424); got != want {
 		t.Errorf("s.Length(): got: %d, want: %d", got, want)
 	}
+
+	if got, want := s.SampleRate(), audioContext.SampleRate(); got != want {
+		t.Errorf("s.SampleRate(): got: %d, want: %d", got, want)
+	}
 }
 
 type reader struct {
@@ -93,9 +95,11 @@ func TestNonSeeker(t *testing.T) {
 		t.Fatal(err)
 	}
 
-	got := s.Length()
-	want := int64(0)
-	if got != want {
+	if got, want := s.Length(), int64(0); got != want {
 		t.Errorf("s.Length(): got: %d, want: %d", got, want)
 	}
+
+	if got, want := s.SampleRate(), audioContext.SampleRate(); got != want {
+		t.Errorf("s.SampleRate(): got: %d, want: %d", got, want)
+	}
 }