abr-controller: fine tune ABR params using best combination found for…

… VoD and Live through AB testing

related to https://github.com/dailymotion/hls.js/pull/467

API.md

@@ -520,21 +520,37 @@ this helps playback continue in certain cases that might otherwise get stuck.
 
 parameter should be a boolean
 
-#### `abrEwmaFast`
+#### ```abrEwmaFastLive```
+(default : 5.0)
+Fast bitrate Exponential moving average half-life , used to compute average bitrate for Live streams
+Half of the estimate is based on the last abrEwmaFastLive seconds of sample history.
+Each of the sample is weighted by the fragment loading duration.
+parameter should be a float greater than 0
 
-(default: `0.0`)
+#### ```abrEwmaSlowLive```
+(default : 9.0)
+
+Slow bitrate Exponential moving average half-life , used to compute average bitrate for Live streams
+Half of the estimate is based on the last abrEwmaSlowLive seconds of sample history.
+Each of the sample is weighted by the fragment loading duration.
+parameter should be a float greater than abrEwmaFastLive
 
-Fast bitrate Exponential moving average half-life , used to compute average bitrate 
-Half of the estimate is based on the last abrEwmaFast seconds of sample history.
-parameter should be a float greater than 0
 
-#### `abrEwmaSlow`
+#### ```abrEwmaFastVoD```
+(default : 4.0)
+
+Fast bitrate Exponential moving average half-life , used to compute average bitrate for VoD streams 
+Half of the estimate is based on the last abrEwmaFastVoD seconds of sample history.
+Each of the sample is weighted by the fragment loading duration.
+parameter should be a float greater than 0
 
-(default: `0.0`)
+#### ```abrEwmaSlowVoD```
+(default : 15.0)
 
-Slow bitrate Exponential moving average half-life , used to compute average bitrate 
-Half of the estimate is based on the last abrEwmaFast seconds of sample history.
-parameter should be a float greater than abrEwmaFast
+Slow bitrate Exponential moving average half-life , used to compute average bitrate for VoD streams 
+Half of the estimate is based on the last abrEwmaSlowVoD seconds of sample history.
+Each of the sample is weighted by the fragment loading duration.
+parameter should be a float greater than abrEwmaFastVoD
 
 
 #### `abrBandWidthFactor`

design.md

@@ -53,7 +53,7 @@ design idea is pretty simple :
        - "expected time of fragment load completion" is computed using "fragment loading instant bandwidth".
        - this time is compared to the "expected time of buffer starvation".
        - if we have less than 2 fragments buffered and if "expected time of fragment load completion" is bigger than "expected time of buffer starvation" and also bigger than duration needed to load fragment at next quality level (determined by auto quality switch algorithm), current fragment loading is aborted, stream-controller will **trigger an emergency switch down**.
-    - auto quality switch algorithm is pretty naive and simple ATM and similar to the one that could be found in google [StageFright](https://android.googlesource.com/platform/frameworks/av/+/master/media/libstagefright/httplive/LiveSession.cpp)   
+    - auto quality switch algorithm is bitrate based : fragment loading bitrate is monitored and smoothed using 2 exponential weighted moving average (a fast one, to adapt quickly on bandwidth drop and a slow one, to avoid ramping up to quickly on bandwidth increase)
   - [src/controller/cap-level-controller.js][]
     - in charge of determining best quality level to actual size (dimensions: width and height) of the player 
   - [src/controller/timeline-controller.js][]

src/controller/abr-controller.js

@@ -21,7 +21,6 @@ class AbrController extends EventHandler {
     this._autoLevelCapping = -1;
     this._nextAutoLevel = -1;
     this.hls = hls;
-    this.bwEstimator = new EwmaBandWidthEstimator(hls);
     this.onCheck = this.abandonRulesCheck.bind(this);
   }
 
@@ -36,6 +35,24 @@ class AbrController extends EventHandler {
       if (!this.timer) {
         this.timer = setInterval(this.onCheck, 100);
       }
+      // lazy init of bw Estimator, rationale is that we use different params for Live/VoD
+      // so we need to wait for stream manifest / playlist type to instantiate it.
+      if (!this.bwEstimator) {
+        let hls = this.hls,
+            level = data.frag.level,
+            isLive = hls.levels[level].details.live,
+            config = hls.config,
+            ewmaFast, ewmaSlow;
+
+        if (isLive) {
+          ewmaFast = config.abrEwmaFastLive;
+          ewmaSlow = config.abrEwmaSlowLive;
+        } else {
+          ewmaFast = config.abrEwmaFastVoD;
+          ewmaSlow = config.abrEwmaSlowVoD;
+        }
+        this.bwEstimator = new EwmaBandWidthEstimator(hls,ewmaSlow,ewmaFast);
+      }
       frag.trequest = performance.now();
       this.fragCurrent = frag;
     }

src/controller/ewma-bandwidth-estimator.js

@@ -11,29 +11,23 @@ import EWMA from '../utils/ewma';
 
 class EwmaBandWidthEstimator {
 
-  constructor(hls) {
+  constructor(hls,slow,fast) {
     this.hls = hls;
     this.defaultEstimate_ = 5e5; // 500kbps
     this.minWeight_ = 0.001;
     this.minDelayMs_ = 50;
+    this.slow_ = new EWMA(slow);
+    this.fast_ = new EWMA(fast);
   }
 
   sample(durationMs,numBytes) {
     durationMs = Math.max(durationMs, this.minDelayMs_);
-    var bandwidth = 8000* numBytes / durationMs;
+    var bandwidth = 8000* numBytes / durationMs,
     //console.log('instant bw:'+ Math.round(bandwidth));
     // we weight sample using loading duration....
-    var weigth = durationMs / 1000;
-
-    // lazy initialization. this allows to take into account config param changes that could happen after Hls instantiation,
-    // but before first fragment loading. this is useful to A/B tests those params
-    if(!this.fast_) {
-      let config = this.hls.config;
-      this.fast_ = new EWMA(config.abrEwmaFast);
-      this.slow_ = new EWMA(config.abrEwmaSlow);
-    }
-    this.fast_.sample(weigth,bandwidth);
-    this.slow_.sample(weigth,bandwidth);
+        weight = durationMs / 1000;
+    this.fast_.sample(weight,bandwidth);
+    this.slow_.sample(weight,bandwidth);
   }
 
 

src/hls.js

@@ -96,8 +96,10 @@ class Hls {
           enableCEA708Captions: true,
           enableMP2TPassThrough : false,
           stretchShortVideoTrack: false,
-          abrEwmaFast: 0,
-          abrEwmaSlow: 0,
+          abrEwmaFastLive: 5,
+          abrEwmaSlowLive: 9,
+          abrEwmaFastVoD: 4,
+          abrEwmaSlowVoD: 15,
           abrBandWidthFactor : 0.8,
           abrBandWidthUpFactor : 0.7
         };