refactor: remove special loadstart handling (#3906)

This is both a change as well as a bug fix. We tried to have better awareness of when the underlying video element changed underneath us so we can dispose of the source handler but that broke some use cases of MSE. Given that we weren't able to fix it in a reasonable non-breaking and non-invasive solution, we're taking it out.

BREAKING CHANGE: remove the double loadstart handlers that dispose the tech/source handlers if a secondary loadstart event is heard.

src/js/tech/tech.js

@@ -1141,12 +1141,6 @@ Tech.withSourceHandlers = function(_Tech) {
 
     if (sh !== _Tech.nativeSourceHandler) {
       this.currentSource_ = source;
-
-      // Catch if someone replaced the src without calling setSource.
-      // If they do, set currentSource_ to null and dispose our source handler.
-      this.off(this.el_, 'loadstart', _Tech.prototype.firstLoadStartListener_);
-      this.off(this.el_, 'loadstart', _Tech.prototype.successiveLoadStartListener_);
-      this.one(this.el_, 'loadstart', _Tech.prototype.firstLoadStartListener_);
     }
 
     this.sourceHandler_ = sh.handleSource(source, this, this.options_);
@@ -1155,26 +1149,6 @@ Tech.withSourceHandlers = function(_Tech) {
     return this;
   };
 
-  /**
-   * Called once for the first loadstart of a video.
-   *
-   * @listens Tech#loadstart
-   */
-  _Tech.prototype.firstLoadStartListener_ = function() {
-    this.one(this.el_, 'loadstart', _Tech.prototype.successiveLoadStartListener_);
-  };
-
-  // On successive loadstarts when setSource has not been called again
-  /**
-   * Called after the first loadstart for a video occurs.
-   *
-   * @listens Tech#loadstart
-   */
-  _Tech.prototype.successiveLoadStartListener_ = function() {
-    this.disposeSourceHandler();
-    this.one(this.el_, 'loadstart', _Tech.prototype.successiveLoadStartListener_);
-  };
-
   /**
    * Clean up any existing SourceHandlers and listeners when the Tech is disposed.
    *
@@ -1193,8 +1167,6 @@ Tech.withSourceHandlers = function(_Tech) {
     this.cleanupAutoTextTracks();
 
     if (this.sourceHandler_) {
-      this.off(this.el_, 'loadstart', _Tech.prototype.firstLoadStartListener_);
-      this.off(this.el_, 'loadstart', _Tech.prototype.successiveLoadStartListener_);
 
       if (this.sourceHandler_.dispose) {
         this.sourceHandler_.dispose();

test/unit/tech/tech.test.js

@@ -506,50 +506,6 @@ QUnit.test('Tech.isTech returns correct answers for techs and components', funct
   assert.ok(!isTech(isTech), 'A function is not a Tech');
 });
 
-QUnit.test('Tech#setSource clears currentSource_ after repeated loadstart', function(assert) {
-  let disposed = false;
-  const MyTech = extendFn(Tech);
-
-  Tech.withSourceHandlers(MyTech);
-  const tech = new MyTech();
-
-  const sourceHandler = {
-    canPlayType(type) {
-      return true;
-    },
-    canHandleSource(source, options) {
-      return true;
-    },
-    handleSource(source, tech_, options) {
-      return {
-        dispose() {
-          disposed = true;
-        }
-      };
-    }
-  };
-
-  // Test registering source handlers
-  MyTech.registerSourceHandler(sourceHandler);
-
-  // First loadstart
-  tech.setSource('test');
-  tech.currentSource_ = 'test';
-  tech.trigger('loadstart');
-  assert.equal(tech.currentSource_, 'test', 'Current source is test');
-
-  // Second loadstart
-  tech.trigger('loadstart');
-  assert.equal(tech.currentSource_, null, 'Current source is null');
-  assert.equal(disposed, true, 'disposed is true');
-
-  // Third loadstart
-  tech.currentSource_ = 'test';
-  tech.trigger('loadstart');
-  assert.equal(tech.currentSource_, null, 'Current source is still null');
-
-});
-
 QUnit.test('setSource after tech dispose should dispose source handler once', function(assert) {
   const MyTech = extendFn(Tech);