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|
package gcc
import (
"math"
"sync"
"time"
)
const (
decreaseEMAAlpha = 0.95
beta = 0.85
)
type rateController struct {
now now
initialTargetBitrate int
minBitrate int
maxBitrate int
dsWriter func(DelayStats)
lock sync.Mutex
init bool
delayStats DelayStats
target int
lastUpdate time.Time
lastState state
latestRTT time.Duration
latestReceivedRate int
latestDecreaseRate *exponentialMovingAverage
}
type exponentialMovingAverage struct {
average float64
variance float64
stdDeviation float64
}
func (a *exponentialMovingAverage) update(value float64) {
if a.average == 0.0 {
a.average = value
} else {
x := value - a.average
a.average += decreaseEMAAlpha * x
a.variance = (1 - decreaseEMAAlpha) * (a.variance + decreaseEMAAlpha*x*x)
a.stdDeviation = math.Sqrt(a.variance)
}
}
func newRateController(now now, initialTargetBitrate, minBitrate, maxBitrate int, dsw func(DelayStats)) *rateController {
return &rateController{
now: now,
initialTargetBitrate: initialTargetBitrate,
minBitrate: minBitrate,
maxBitrate: maxBitrate,
dsWriter: dsw,
init: false,
delayStats: DelayStats{},
target: initialTargetBitrate,
lastUpdate: time.Time{},
lastState: stateIncrease,
latestRTT: 0,
latestReceivedRate: 0,
latestDecreaseRate: &exponentialMovingAverage{},
}
}
func (c *rateController) onReceivedRate(rate int) {
c.lock.Lock()
defer c.lock.Unlock()
c.latestReceivedRate = rate
}
func (c *rateController) updateRTT(rtt time.Duration) {
c.lock.Lock()
defer c.lock.Unlock()
c.latestRTT = rtt
}
func (c *rateController) onDelayStats(ds DelayStats) {
now := time.Now()
if !c.init {
c.delayStats = ds
c.delayStats.State = stateIncrease
c.init = true
return
}
c.delayStats = ds
c.delayStats.State = c.delayStats.State.transition(ds.Usage)
if c.delayStats.State == stateHold {
return
}
var next DelayStats
c.lock.Lock()
switch c.delayStats.State {
case stateHold:
// should never occur due to check above, but makes the linter happy
case stateIncrease:
c.target = clampInt(c.increase(now), c.minBitrate, c.maxBitrate)
next = DelayStats{
Measurement: c.delayStats.Measurement,
Estimate: c.delayStats.Estimate,
Threshold: c.delayStats.Threshold,
LastReceiveDelta: c.delayStats.LastReceiveDelta,
Usage: c.delayStats.Usage,
State: c.delayStats.State,
TargetBitrate: c.target,
}
case stateDecrease:
c.target = clampInt(c.decrease(), c.minBitrate, c.maxBitrate)
next = DelayStats{
Measurement: c.delayStats.Measurement,
Estimate: c.delayStats.Estimate,
Threshold: c.delayStats.Threshold,
LastReceiveDelta: c.delayStats.LastReceiveDelta,
Usage: c.delayStats.Usage,
State: c.delayStats.State,
TargetBitrate: c.target,
}
}
c.lock.Unlock()
c.dsWriter(next)
}
func (c *rateController) increase(now time.Time) int {
if c.latestDecreaseRate.average > 0 && float64(c.latestReceivedRate) > c.latestDecreaseRate.average-3*c.latestDecreaseRate.stdDeviation &&
float64(c.latestReceivedRate) < c.latestDecreaseRate.average+3*c.latestDecreaseRate.stdDeviation {
bitsPerFrame := float64(c.target) / 30.0
packetsPerFrame := math.Ceil(bitsPerFrame / (1200 * 8))
expectedPacketSizeBits := bitsPerFrame / packetsPerFrame
responseTime := 100*time.Millisecond + c.latestRTT
alpha := 0.5 * math.Min(float64(now.Sub(c.lastUpdate).Milliseconds())/float64(responseTime.Milliseconds()), 1.0)
increase := int(math.Max(1000.0, alpha*expectedPacketSizeBits))
c.lastUpdate = now
return int(math.Min(float64(c.target+increase), 1.5*float64(c.latestReceivedRate)))
}
eta := math.Pow(1.08, math.Min(float64(now.Sub(c.lastUpdate).Milliseconds())/1000, 1.0))
c.lastUpdate = now
rate := int(eta * float64(c.target))
// maximum increase to 1.5 * received rate
received := int(1.5 * float64(c.latestReceivedRate))
if rate > received && received > c.target {
return received
}
if rate < c.target {
return c.target
}
return rate
}
func (c *rateController) decrease() int {
target := int(beta * float64(c.latestReceivedRate))
c.latestDecreaseRate.update(float64(c.latestReceivedRate))
c.lastUpdate = c.now()
return target
}
|
