Merge pull request #4 from gesinger/ewma-selector-minor-changes

Change binds in moving average test to calls

src/playlist-selectors.js

@@ -196,6 +196,8 @@ const simpleSelector = function(master, bandwidth, width, height) {
  * Chooses the appropriate media playlist based on the most recent
  * bandwidth estimate and the player size.
  *
+ * Expects to be called within the context of an instance of HlsHandler
+ *
  * @return {Playlist} the highest bitrate playlist less than the
  * currently detected bandwidth, accounting for some amount of
  * bandwidth variance
@@ -212,6 +214,8 @@ export const lastBandwidthSelector = function() {
  * exponential-weighted moving average of the bandwidth after
  * filtering for player size.
  *
+ * Expects to be called within the context of an instance of HlsHandler
+ *
  * @param {Number} decay - a number between 0 and 1. Higher values of
  * this parameter will cause previous bandwidth estimates to lose
  * significance more quickly.

test/playlist-selectors.test.js

@@ -28,25 +28,26 @@ test('Exponential moving average has a configurable decay parameter', function(a
     { attributes: { BANDWIDTH: 100 } }
   ];
   hls.systemBandwidth = 50 * Config.BANDWIDTH_VARIANCE + 1;
-  playlist = instantAverage.bind(hls)();
+  playlist = instantAverage.call(hls);
   assert.equal(playlist.attributes.BANDWIDTH, 50, 'selected the middle playlist');
 
   hls.systemBandwidth = 100 * Config.BANDWIDTH_VARIANCE + 1;
-  playlist = instantAverage.bind(hls)();
+  playlist = instantAverage.call(hls);
   assert.equal(playlist.attributes.BANDWIDTH, 100, 'selected the top playlist');
 
   const fiftyPercentDecay = movingAverageBandwidthSelector(0.5);
 
   hls.systemBandwidth = 100 * Config.BANDWIDTH_VARIANCE + 1;
-  playlist = fiftyPercentDecay.bind(hls)();
+  playlist = fiftyPercentDecay.call(hls);
   assert.equal(playlist.attributes.BANDWIDTH, 100, 'selected the top playlist');
 
+  // average = decay * systemBandwidth + (1 - decay) * average
   // bandwidth = 0.5 * systemBandwidth + 0.5 * (100 * variance + 1)
   // 50 * variance + 1 = 0.5 * (systemBandwidth + (100 * variance + 1))
   // 2 * 50 * variance + 2 = systemBandwidth + (100 * variance + 1)
   // 100 * variance + 2 - (100 * variance + 1) = systemBandwidth
   // 1 = systemBandwidth
   hls.systemBandwidth = 1;
-  playlist = fiftyPercentDecay.bind(hls)();
+  playlist = fiftyPercentDecay.call(hls);
   assert.equal(playlist.attributes.BANDWIDTH, 50, 'selected the middle playlist');
 });