feat(ABR): Add cacheLoadThreshold config (shaka-project#6657)

Close shaka-project#6623

demo/config.js

@@ -305,6 +305,9 @@ shakaDemo.Config = class {
             'abr.clearBufferSwitch')
         .addNumberInput_('Safe margin on abr switch rendition',
             'abr.safeMarginSwitch',
+            /* canBeDecimal= */ true)
+        .addNumberInput_('Milliseconds to consider a request cached',
+            'abr.cacheLoadThreshold',
             /* canBeDecimal= */ true);
     this.addRetrictionsSection_('abr', 'Adaptation Restrictions');
   }

externs/shaka/player.js

@@ -1567,7 +1567,8 @@ shaka.extern.AdsConfiguration;
  *   restrictToScreenSize: boolean,
  *   ignoreDevicePixelRatio: boolean,
  *   clearBufferSwitch: boolean,
- *   safeMarginSwitch: number
+ *   safeMarginSwitch: number,
+ *   cacheLoadThreshold: number
  * }}
  *
  * @property {boolean} enabled
@@ -1625,6 +1626,10 @@ shaka.extern.AdsConfiguration;
  *   Can cause hiccups on some browsers if chosen too small, e.g.
  *   The amount of two segments is a fair minimum to consider as safeMargin
  *   value.
+ * @property {number} cacheLoadThreshold
+ *   Indicates the value in milliseconds from which a request is not
+ *   considered cached.
+ *   Defaults to <code>20</code>.
  * @exportDoc
  */
 shaka.extern.AbrConfiguration;

lib/abr/simple_abr_manager.js

@@ -308,6 +308,11 @@ shaka.abr.SimpleAbrManager = class {
    * @export
    */
   segmentDownloaded(deltaTimeMs, numBytes, allowSwitch, request) {
+    if (deltaTimeMs < this.config_.cacheLoadThreshold) {
+      // The time indicates that it could be a cache response, so we should
+      // ignore this value.
+      return;
+    }
     shaka.log.v2('Segment downloaded:',
         'contentType=' + (request && request.contentType),
         'deltaTimeMs=' + deltaTimeMs,

lib/util/player_configuration.js

@@ -333,6 +333,7 @@ shaka.util.PlayerConfiguration = class {
       ignoreDevicePixelRatio: false,
       clearBufferSwitch: false,
       safeMarginSwitch: 0,
+      cacheLoadThreshold: 20,
     };
 
     const cmcd = {