Optimize ToI420 conversion by using sync.Pool (#473)

Added sync.Pool to the i420 conversion to minimize overhead of creating new byte slices

pkg/codec/mmal/mmal.go

@@ -64,10 +64,11 @@ func (e *encoder) Read() ([]byte, func(), error) {
 		return nil, func() {}, io.EOF
 	}
 
-	img, _, err := e.r.Read()
+	img, release, err := e.r.Read()
 	if err != nil {
 		return nil, func() {}, err
 	}
+	defer release()
 	imgReal := img.(*image.YCbCr)
 	var y, cb, cr C.Slice
 	y.data = (*C.uchar)(&imgReal.Y[0])

pkg/codec/openh264/openh264.go

@@ -65,10 +65,11 @@ func (e *encoder) Read() ([]byte, func(), error) {
 		return nil, func() {}, io.EOF
 	}
 
-	img, _, err := e.r.Read()
+	img, release, err := e.r.Read()
 	if err != nil {
 		return nil, func() {}, err
 	}
+	defer release()
 
 	yuvImg := img.(*image.YCbCr)
 	bounds := yuvImg.Bounds()

pkg/codec/vaapi/vp8.go

@@ -304,10 +304,11 @@ func (e *encoderVP8) Read() ([]byte, func(), error) {
 		return nil, func() {}, io.EOF
 	}
 
-	img, _, err := e.r.Read()
+	img, release, err := e.r.Read()
 	if err != nil {
 		return nil, func() {}, err
 	}
+	defer release()
 	yuvImg := img.(*image.YCbCr)
 
 	kf := e.frameCnt%e.params.KeyFrameInterval == 0

pkg/codec/vaapi/vp9.go

@@ -293,10 +293,11 @@ func (e *encoderVP9) Read() ([]byte, func(), error) {
 		return nil, func() {}, io.EOF
 	}
 
-	img, _, err := e.r.Read()
+	img, release, err := e.r.Read()
 	if err != nil {
 		return nil, func() {}, err
 	}
+	defer release()
 	yuvImg := img.(*image.YCbCr)
 
 	kf := e.frameCnt%e.params.KeyFrameInterval == 0

pkg/codec/vpx/vpx.go

@@ -219,10 +219,11 @@ func (e *encoder) Read() ([]byte, func(), error) {
 		return nil, func() {}, io.EOF
 	}
 
-	img, _, err := e.r.Read()
+	img, release, err := e.r.Read()
 	if err != nil {
 		return nil, func() {}, err
 	}
+	defer release()
 	yuvImg := img.(*image.YCbCr)
 	bounds := yuvImg.Bounds()
 	height := C.int(bounds.Dy())

pkg/codec/x264/x264.go

@@ -102,10 +102,11 @@ func (e *encoder) Read() ([]byte, func(), error) {
 		return nil, func() {}, io.EOF
 	}
 
-	img, _, err := e.r.Read()
+	img, release, err := e.r.Read()
 	if err != nil {
 		return nil, func() {}, err
 	}
+	defer release()
 	yuvImg := img.(*image.YCbCr)
 
 	var rc C.int

pkg/io/video/convert.go

@@ -4,6 +4,7 @@ import (
 	"fmt"
 	"image"
 	"image/color"
+	"sync"
 )
 
 // imageToYCbCr converts src to *image.YCbCr and store it to dst
@@ -60,29 +61,61 @@ func imageToYCbCr(dst *image.YCbCr, src image.Image) {
 	}
 }
 
+// bytePool stores slices to be reused
+// New method is not set as the slice size
+// should be allocated according to subsample ratio
+var bytesPool sync.Pool
+
 // ToI420 converts r to a new reader that will output images in I420 format
 func ToI420(r Reader) Reader {
 	var yuvImg image.YCbCr
+
+	getSlice := func(cLen int) []uint8 {
+		// Retrieve slice from pool
+		dst, ok := bytesPool.Get().([]byte)
+
+		// Compare value or capacity of retrieved object
+		// If less than expected, reallocate new object
+		if !ok || cap(dst) < 2*cLen {
+			// Allocating memory for Cb and Cr
+			dst = make([]byte, 2*cLen, 2*cLen)
+		}
+
+		return dst
+	}
+
 	return ReaderFunc(func() (image.Image, func(), error) {
 		img, _, err := r.Read()
 		if err != nil {
 			return nil, func() {}, err
 		}
 
+		var releaseFunc func() = func() {}
+
 		imageToYCbCr(&yuvImg, img)
 
 		// Covert pixel format to I420
 		switch yuvImg.SubsampleRatio {
 		case image.YCbCrSubsampleRatio420:
 		case image.YCbCrSubsampleRatio444:
-			yuvImg = i444ToI420(yuvImg)
+			cLen := yuvImg.CStride * yuvImg.Rect.Dy() / 4
+			dst := getSlice(cLen)
+			yuvImg = i444ToI420(yuvImg, dst)
+			releaseFunc = func() {
+				bytesPool.Put(dst)
+			}
 		case image.YCbCrSubsampleRatio422:
-			yuvImg = i422ToI420(yuvImg)
+			cLen := yuvImg.CStride * (yuvImg.Rect.Dy() / 2)
+			dst := getSlice(cLen)
+			yuvImg = i422ToI420(yuvImg, dst)
+			releaseFunc = func() {
+				bytesPool.Put(dst)
+			}
 		default:
-			return nil, func() {}, fmt.Errorf("unsupported pixel format: %s", yuvImg.SubsampleRatio)
+			return nil, releaseFunc, fmt.Errorf("unsupported pixel format: %s", yuvImg.SubsampleRatio)
 		}
 
-		return &yuvImg, func() {}, nil
+		return &yuvImg, releaseFunc, nil
 	})
 }
 

pkg/io/video/convert_cgo.go

@@ -15,10 +15,13 @@ import "C"
 // All functions switched at runtime must be declared also in convert_nocgo.go.
 const hasCGOConvert = true
 
-func i444ToI420(img image.YCbCr) image.YCbCr {
+func i444ToI420(img image.YCbCr, dst []uint8) image.YCbCr {
 	h := img.Rect.Dy()
 	cLen := img.CStride * h / 4
-	cbDst, crDst := make([]uint8, cLen), make([]uint8, cLen)
+	// Divide preallocated memory to cbDst and crDst
+	// and truncate cap and len to cLen
+	cbDst, crDst := dst[:cLen:cLen], dst[cLen:]
+	crDst = crDst[:cLen:cLen]
 	C.i444ToI420CGO(
 		(*C.uchar)(&cbDst[0]), (*C.uchar)(&crDst[0]),
 		(*C.uchar)(&img.Cb[0]), (*C.uchar)(&img.Cr[0]),
@@ -31,10 +34,13 @@ func i444ToI420(img image.YCbCr) image.YCbCr {
 	return img
 }
 
-func i422ToI420(img image.YCbCr) image.YCbCr {
+func i422ToI420(img image.YCbCr, dst []uint8) image.YCbCr {
 	h := img.Rect.Dy()
 	cLen := img.CStride * (h / 2)
-	cbDst, crDst := make([]uint8, cLen), make([]uint8, cLen)
+	// Divide preallocated memory to cbDst and crDst
+	// and truncate cap and len to cLen
+	cbDst, crDst := dst[:cLen:cLen], dst[cLen:]
+	crDst = crDst[:cLen:cLen]
 	C.i422ToI420CGO(
 		(*C.uchar)(&cbDst[0]), (*C.uchar)(&crDst[0]),
 		(*C.uchar)(&img.Cb[0]), (*C.uchar)(&img.Cr[0]),

pkg/io/video/convert_nocgo.go

@@ -10,13 +10,16 @@ import (
 
 const hasCGOConvert = false
 
-func i444ToI420(img image.YCbCr) image.YCbCr {
+func i444ToI420(img image.YCbCr, dst []uint8) image.YCbCr {
 	h := img.Rect.Dy()
 	addrSrc0 := 0
 	addrSrc1 := img.CStride
 	cLen := img.CStride * (h / 2)
 	addrDst := 0
-	cbDst, crDst := make([]uint8, cLen), make([]uint8, cLen)
+	// Divide preallocated memory to cbDst and crDst
+	// and truncate cap and len to cLen
+	cbDst, crDst := dst[:cLen:cLen], dst[cLen:]
+	crDst = crDst[:cLen:cLen]
 
 	for i := 0; i < h/2; i++ {
 		for j := 0; j < img.CStride/2; j++ {
@@ -40,11 +43,14 @@ func i444ToI420(img image.YCbCr) image.YCbCr {
 	return img
 }
 
-func i422ToI420(img image.YCbCr) image.YCbCr {
+func i422ToI420(img image.YCbCr, dst []uint8) image.YCbCr {
 	h := img.Rect.Dy()
 	addrSrc := 0
 	cLen := img.CStride * (h / 2)
-	cbDst, crDst := make([]uint8, cLen), make([]uint8, cLen)
+	// Divide preallocated memory to cbDst and crDst
+	// and truncate cap and len to cLen
+	cbDst, crDst := dst[:cLen:cLen], dst[cLen:]
+	crDst = crDst[:cLen:cLen]
 	addrDst := 0
 
 	for i := 0; i < h/2; i++ {

pkg/io/video/convert_test.go

@@ -147,10 +147,11 @@ func TestToI420(t *testing.T) {
 			r := ToI420(ReaderFunc(func() (image.Image, func(), error) {
 				return c.src, func() {}, nil
 			}))
-			out, _, err := r.Read()
+			out, release, err := r.Read()
 			if err != nil {
 				t.Fatalf("Unexpected error: %v", err)
 			}
+			defer release()
 			if !reflect.DeepEqual(c.expected, out) {
 				t.Errorf("Expected output image:\n%v\ngot:\n%v", c.expected, out)
 			}
@@ -230,10 +231,11 @@ func BenchmarkToI420(b *testing.B) {
 					}))
 
 					for i := 0; i < b.N; i++ {
-						_, _, err := r.Read()
+						_, release, err := r.Read()
 						if err != nil {
 							b.Fatalf("Unexpected error: %v", err)
 						}
+						release()
 					}
 				})
 			}