From 733188ab176b34f8f4744d42ef4ad87b08f2284f Mon Sep 17 00:00:00 2001
From: Sean DuBois <duboisea@justin.tv>
Date: Fri, 30 Sep 2022 21:56:49 -0600
Subject: [PATCH] Implement bitdepth conversion and upsampling

bitdepth package takes F32LE -> S16LE and handles upsampling
from 16Khz -> 48Khz
---
 decoder.go                         | 11 +++++++++--
 examples/decode/README.md          |  4 ++--
 examples/decode/main.go            | 12 +++---------
 internal/bitdepth/bitdepth.go      | 22 ++++++++++++++++++++++
 internal/bitdepth/bitdepth_test.go | 16 ++++++++++++++++
 internal/bitdepth/errors.go        |  7 +++++++
 6 files changed, 59 insertions(+), 13 deletions(-)
 create mode 100644 internal/bitdepth/bitdepth.go
 create mode 100644 internal/bitdepth/bitdepth_test.go
 create mode 100644 internal/bitdepth/errors.go

diff --git a/decoder.go b/decoder.go
index eaad268..882452b 100644
--- a/decoder.go
+++ b/decoder.go
@@ -3,23 +3,26 @@ package opus
 import (
 	"fmt"
 
+	"github.com/pion/opus/internal/bitdepth"
 	"github.com/pion/opus/internal/silk"
 )
 
 // Decoder decodes the Opus bitstream into PCM
 type Decoder struct {
 	silkDecoder silk.Decoder
+	silkBuffer  []float32
 }
 
 // NewDecoder creates a new Opus Decoder
 func NewDecoder() Decoder {
 	return Decoder{
 		silkDecoder: silk.NewDecoder(),
+		silkBuffer:  make([]float32, 320),
 	}
 }
 
 // Decode decodes the Opus bitstream into PCM
-func (d *Decoder) Decode(in []byte, out []float32) (bandwidth Bandwidth, isStereo bool, err error) {
+func (d *Decoder) Decode(in []byte, out []byte) (bandwidth Bandwidth, isStereo bool, err error) {
 	if len(in) < 1 {
 		return 0, false, errTooShortForTableOfContentsHeader
 	}
@@ -40,11 +43,15 @@ func (d *Decoder) Decode(in []byte, out []float32) (bandwidth Bandwidth, isStere
 	}
 
 	for _, encodedFrame := range encodedFrames {
-		err := d.silkDecoder.Decode(encodedFrame, out, tocHeader.isStereo(), cfg.frameDuration().nanoseconds(), silk.Bandwidth(cfg.bandwidth()))
+		err := d.silkDecoder.Decode(encodedFrame, d.silkBuffer, tocHeader.isStereo(), cfg.frameDuration().nanoseconds(), silk.Bandwidth(cfg.bandwidth()))
 		if err != nil {
 			return 0, false, err
 		}
 	}
 
+	if err := bitdepth.ConvertFloat32LittleEndianToSigned16LittleEndian(d.silkBuffer, out, 3); err != nil {
+		return 0, false, err
+	}
+
 	return cfg.bandwidth(), tocHeader.isStereo(), nil
 }
diff --git a/examples/decode/README.md b/examples/decode/README.md
index bbeef3a..3cfa5ea 100644
--- a/examples/decode/README.md
+++ b/examples/decode/README.md
@@ -28,9 +28,9 @@ decoder `pwd`/output.ogg `audio-samples.pcm`
 Now play the audio with the tool of your choice.
 
 ```
-gst-launch-1.0 filesrc location=audio-samples.pcm ! audio/x-raw, format=F32LE, rate=16000,channels=1  ! autoaudiosink -v
+gst-launch-1.0 filesrc location=audio-samples.pcm ! audio/x-raw, format=S16LE, rate=48000,channels=1  ! autoaudiosink -v
 ```
 
 ```
-ffplay -f f32le -ar 16000 audio-samples.pcm
+ffplay -f s16le -ar 48000 audio-samples.pcm
 ```
diff --git a/examples/decode/main.go b/examples/decode/main.go
index d2e895c..24c42fe 100644
--- a/examples/decode/main.go
+++ b/examples/decode/main.go
@@ -2,7 +2,6 @@ package main
 
 import (
 	"bytes"
-	"encoding/binary"
 	"errors"
 	"io"
 	"os"
@@ -11,12 +10,6 @@ import (
 	"github.com/pion/opus/pkg/oggreader"
 )
 
-func convertFloatToByteSlice(i []float32) []byte {
-	buf := new(bytes.Buffer)
-	binary.Write(buf, binary.LittleEndian, i)
-	return buf.Bytes()
-}
-
 func main() {
 	if len(os.Args) != 3 {
 		panic("Usage: <in-file> <out-file>")
@@ -32,13 +25,14 @@ func main() {
 		panic(err)
 	}
 
-	out := make([]float32, 320)
+	out := make([]byte, 1920)
 	f, err := os.Create(os.Args[2])
 	if err != nil {
 		panic(err)
 	}
 
 	decoder := opus.NewDecoder()
+	x := 0
 	for {
 		segments, _, err := ogg.ParseNextPage()
 
@@ -57,7 +51,7 @@ func main() {
 				panic(err)
 			}
 
-			f.Write(convertFloatToByteSlice(out))
+			f.Write(out)
 		}
 	}
 }
diff --git a/internal/bitdepth/bitdepth.go b/internal/bitdepth/bitdepth.go
new file mode 100644
index 0000000..6fa96fb
--- /dev/null
+++ b/internal/bitdepth/bitdepth.go
@@ -0,0 +1,22 @@
+package bitdepth
+
+import (
+	"math"
+)
+
+func ConvertFloat32LittleEndianToSigned16LittleEndian(in []float32, out []byte, resampleCount int) error {
+	currIndex := 0
+	for i := range in {
+		res := int16(math.Floor(float64(in[i] * 32767)))
+
+		for j := resampleCount; j > 0; j-- {
+			out[currIndex] = byte(res & 0b11111111)
+			currIndex++
+
+			out[currIndex] = (byte(res >> 8))
+			currIndex++
+		}
+	}
+
+	return nil
+}
diff --git a/internal/bitdepth/bitdepth_test.go b/internal/bitdepth/bitdepth_test.go
new file mode 100644
index 0000000..5a95b3c
--- /dev/null
+++ b/internal/bitdepth/bitdepth_test.go
@@ -0,0 +1,16 @@
+package bitdepth
+
+import (
+	"bytes"
+	"testing"
+)
+
+func TestConvertFloat32LittleEndianToSigned16LittleEndian(t *testing.T) {
+	in := []float32{0.3, 0, .55, .72, -.05}
+	out := make([]byte, len(in)*2)
+	ConvertFloat32LittleEndianToSigned16LittleEndian(in, out, 1)
+
+	if !bytes.Equal([]byte{0x66, 0x26, 0x00, 0x00, 0x65, 0x46, 0x28, 0x5c, 0x99, 0xf9}, out) {
+		t.Fatal("buffer mismatch")
+	}
+}
diff --git a/internal/bitdepth/errors.go b/internal/bitdepth/errors.go
new file mode 100644
index 0000000..75e4e3d
--- /dev/null
+++ b/internal/bitdepth/errors.go
@@ -0,0 +1,7 @@
+package bitdepth
+
+import "errors"
+
+var (
+	errBufferLengthMismatch = errors.New("length of in and out buffer are not equal")
+)