[VPX] vpx dynamic encoding (#647)

* Add vp8 decoder and dynamic vp8 decoding

* Add QPController

* change parameters into const

* move decoder into another PR

* use explicit parameter name

pkg/codec/vpx/vpx_test.go

@@ -4,6 +4,8 @@ import (
 	"context"
 	"image"
 	"io"
+	"math"
+	"math/rand"
 	"sync/atomic"
 	"testing"
 	"time"
@@ -13,6 +15,7 @@ import (
 	"github.com/pion/mediadevices/pkg/frame"
 	"github.com/pion/mediadevices/pkg/io/video"
 	"github.com/pion/mediadevices/pkg/prop"
+	"github.com/stretchr/testify/assert"
 )
 
 func TestEncoder(t *testing.T) {
@@ -360,3 +363,65 @@ func TestEncoderFrameMonotonic(t *testing.T) {
 		}
 	}
 }
+
+func TestVP8DynamicQPControl(t *testing.T) {
+	t.Run("VP8", func(t *testing.T) {
+		p, err := NewVP8Params()
+		if err != nil {
+			t.Fatal(err)
+		}
+		p.LagInFrames = 0 // Disable frame lag buffering for real-time encoding
+		p.RateControlEndUsage = RateControlCBR
+		totalFrames := 100
+		frameRate := 10
+		initialWidth, initialHeight := 800, 600
+		var cnt uint32
+
+		r, err := p.BuildVideoEncoder(
+			video.ReaderFunc(func() (image.Image, func(), error) {
+				i := atomic.AddUint32(&cnt, 1)
+				if i == uint32(totalFrames+1) {
+					return nil, nil, io.EOF
+				}
+				img := image.NewYCbCr(image.Rect(0, 0, initialWidth, initialHeight), image.YCbCrSubsampleRatio420)
+				r := rand.New(rand.NewSource(time.Now().UnixNano()))
+				for i := range img.Y {
+					img.Y[i] = uint8(r.Intn(256))
+				}
+				for i := range img.Cb {
+					img.Cb[i] = uint8(r.Intn(256))
+				}
+				for i := range img.Cr {
+					img.Cr[i] = uint8(r.Intn(256))
+				}
+				return img, func() {}, nil
+			}),
+			prop.Media{
+				Video: prop.Video{
+					Width:       initialWidth,
+					Height:      initialHeight,
+					FrameRate:   float32(frameRate),
+					FrameFormat: frame.FormatI420,
+				},
+			},
+		)
+		if err != nil {
+			t.Fatal(err)
+		}
+		initialBitrate := 100
+		currentBitrate := initialBitrate
+		targetBitrate := 300
+		for i := 0; i < totalFrames; i++ {
+			r.Controller().(codec.KeyFrameController).ForceKeyFrame()
+			r.Controller().(codec.QPController).DynamicQPControl(currentBitrate, targetBitrate)
+			data, rel, err := r.Read()
+			if err != nil {
+				t.Fatal(err)
+			}
+			rel()
+			encodedSize := len(data)
+			currentBitrate = encodedSize * 8 / 1000 / frameRate
+		}
+		assert.Less(t, math.Abs(float64(targetBitrate-currentBitrate)), math.Abs(float64(initialBitrate-currentBitrate)))
+	})
+}