wave: add SubAudio method

SubAudio returns part of the original audio sharing the buffer.

pkg/wave/float32.go

@@ -34,6 +34,16 @@ func (a *Float32Interleaved) SetFloat32(i, ch int, s Float32Sample) {
 	a.Data[i*a.Size.Channels+ch] = float32(s)
 }
 
+// SubAudio returns part of the original audio sharing the buffer.
+func (a *Float32Interleaved) SubAudio(offsetSamples, nSamples int) *Float32Interleaved {
+	ret := *a
+	offset := offsetSamples * a.Size.Channels
+	n := nSamples * a.Size.Channels
+	ret.Data = ret.Data[offset : offset+n]
+	ret.Size.Len = nSamples
+	return &ret
+}
+
 func NewFloat32Interleaved(size ChunkInfo) *Float32Interleaved {
 	return &Float32Interleaved{
 		Data: make([]float32, size.Channels*size.Len),
@@ -68,6 +78,16 @@ func (a *Float32NonInterleaved) SetFloat32(i, ch int, s Float32Sample) {
 	a.Data[ch][i] = float32(s)
 }
 
+// SubAudio returns part of the original audio sharing the buffer.
+func (a *Float32NonInterleaved) SubAudio(offsetSamples, nSamples int) *Float32NonInterleaved {
+	ret := *a
+	for i := range a.Data {
+		ret.Data[i] = ret.Data[i][offsetSamples : offsetSamples+nSamples]
+	}
+	ret.Size.Len = nSamples
+	return &ret
+}
+
 func NewFloat32NonInterleaved(size ChunkInfo) *Float32NonInterleaved {
 	d := make([][]float32, size.Channels)
 	for i := 0; i < size.Channels; i++ {

pkg/wave/float32_test.go

@@ -51,3 +51,44 @@ func TestFloat32(t *testing.T) {
 		})
 	}
 }
+
+func TestFloat32SubAudio(t *testing.T) {
+	t.Run("Interleaved", func(t *testing.T) {
+		in := &Float32Interleaved{
+			Data: []float32{
+				0.1, -0.5, 0.2, -0.6, 0.3, -0.7, 0.4, -0.8, 0.5, -0.9, 0.6, -1.0, 0.7, -1.1, 0.8, -1.2,
+			},
+			Size: ChunkInfo{8, 2, 48000},
+		}
+		expected := &Float32Interleaved{
+			Data: []float32{
+				0.3, -0.7, 0.4, -0.8, 0.5, -0.9,
+			},
+			Size: ChunkInfo{3, 2, 48000},
+		}
+		out := in.SubAudio(2, 3)
+		if !reflect.DeepEqual(expected, out) {
+			t.Errorf("SubAudio differs, expected: %v, got: %v", expected, out)
+		}
+	})
+	t.Run("NonInterleaved", func(t *testing.T) {
+		in := &Float32NonInterleaved{
+			Data: [][]float32{
+				{0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8},
+				{-0.5, -0.6, -0.7, -0.8, -0.9, -1.0, -1.1, -1.2},
+			},
+			Size: ChunkInfo{8, 2, 48000},
+		}
+		expected := &Float32NonInterleaved{
+			Data: [][]float32{
+				{0.3, 0.4, 0.5},
+				{-0.7, -0.8, -0.9},
+			},
+			Size: ChunkInfo{3, 2, 48000},
+		}
+		out := in.SubAudio(2, 3)
+		if !reflect.DeepEqual(expected, out) {
+			t.Errorf("SubAudio differs, expected: %v, got: %v", expected, out)
+		}
+	})
+}

pkg/wave/int16.go

@@ -34,6 +34,16 @@ func (a *Int16Interleaved) SetInt16(i, ch int, s Int16Sample) {
 	a.Data[i*a.Size.Channels+ch] = int16(s)
 }
 
+// SubAudio returns part of the original audio sharing the buffer.
+func (a *Int16Interleaved) SubAudio(offsetSamples, nSamples int) *Int16Interleaved {
+	ret := *a
+	offset := offsetSamples * a.Size.Channels
+	n := nSamples * a.Size.Channels
+	ret.Data = ret.Data[offset : offset+n]
+	ret.Size.Len = nSamples
+	return &ret
+}
+
 func NewInt16Interleaved(size ChunkInfo) *Int16Interleaved {
 	return &Int16Interleaved{
 		Data: make([]int16, size.Channels*size.Len),
@@ -68,6 +78,16 @@ func (a *Int16NonInterleaved) SetInt16(i, ch int, s Int16Sample) {
 	a.Data[ch][i] = int16(s)
 }
 
+// SubAudio returns part of the original audio sharing the buffer.
+func (a *Int16NonInterleaved) SubAudio(offsetSamples, nSamples int) *Int16NonInterleaved {
+	ret := *a
+	for i := range a.Data {
+		ret.Data[i] = ret.Data[i][offsetSamples : offsetSamples+nSamples]
+	}
+	ret.Size.Len = nSamples
+	return &ret
+}
+
 func NewInt16NonInterleaved(size ChunkInfo) *Int16NonInterleaved {
 	d := make([][]int16, size.Channels)
 	for i := 0; i < size.Channels; i++ {

pkg/wave/int16_test.go

@@ -51,3 +51,44 @@ func TestInt16(t *testing.T) {
 		})
 	}
 }
+
+func TestInt32SubAudio(t *testing.T) {
+	t.Run("Interleaved", func(t *testing.T) {
+		in := &Int16Interleaved{
+			Data: []int16{
+				1, -5, 2, -6, 3, -7, 4, -8, 5, -9, 6, -10, 7, -11, 8, -12,
+			},
+			Size: ChunkInfo{8, 2, 48000},
+		}
+		expected := &Int16Interleaved{
+			Data: []int16{
+				3, -7, 4, -8, 5, -9,
+			},
+			Size: ChunkInfo{3, 2, 48000},
+		}
+		out := in.SubAudio(2, 3)
+		if !reflect.DeepEqual(expected, out) {
+			t.Errorf("SubAudio differs, expected: %v, got: %v", expected, out)
+		}
+	})
+	t.Run("NonInterleaved", func(t *testing.T) {
+		in := &Int16NonInterleaved{
+			Data: [][]int16{
+				{1, 2, 3, 4, 5, 6, 7, 8},
+				{-5, -6, -7, -8, -9, -10, -11, -12},
+			},
+			Size: ChunkInfo{8, 2, 48000},
+		}
+		expected := &Int16NonInterleaved{
+			Data: [][]int16{
+				{3, 4, 5},
+				{-7, -8, -9},
+			},
+			Size: ChunkInfo{3, 2, 48000},
+		}
+		out := in.SubAudio(2, 3)
+		if !reflect.DeepEqual(expected, out) {
+			t.Errorf("SubAudio differs, expected: %v, got: %v", expected, out)
+		}
+	})
+}