fix: don't decay average bandwidth value if system bandwidth did not …

…change (#1137)

src/playlist-selectors.js

@@ -364,6 +364,7 @@ export const lastBandwidthSelector = function() {
  */
 export const movingAverageBandwidthSelector = function(decay) {
   let average = -1;
+  let lastSystemBandwidth = -1;
 
   if (decay < 0 || decay > 1) {
     throw new Error('Moving average bandwidth decay must be between 0 and 1.');
@@ -374,9 +375,20 @@ export const movingAverageBandwidthSelector = function(decay) {
 
     if (average < 0) {
       average = this.systemBandwidth;
+      lastSystemBandwidth = this.systemBandwidth;
+    }
+
+    // stop the average value from decaying for every 250ms
+    // when the systemBandwidth is constant
+    // and
+    // stop average from setting to a very low value when the
+    // systemBandwidth becomes 0 in case of chunk cancellation
+
+    if (this.systemBandwidth > 0 && this.systemBandwidth !== lastSystemBandwidth) {
+      average = decay * this.systemBandwidth + (1 - decay) * average;
+      lastSystemBandwidth = this.systemBandwidth;
     }
 
-    average = decay * this.systemBandwidth + (1 - decay) * average;
     return simpleSelector(
       this.playlists.master,
       average,