perf: Region timeline improvements (#8203)

- Only run filter timer if we have any region cached
- use map for faster lookup

lib/media/region_timeline.js

@@ -28,8 +28,8 @@ shaka.media.RegionTimeline = class extends shaka.util.FakeEventTarget {
   constructor(getSeekRange) {
     super();
 
-    /** @private {!Set<T>} */
-    this.regions_ = new Set();
+    /** @private {!Map<string, T>} */
+    this.regions_ = new Map();
 
     /** @private {!function():{start: number, end: number}} */
     this.getSeekRange_ = getSeekRange;
@@ -41,33 +41,31 @@ shaka.media.RegionTimeline = class extends shaka.util.FakeEventTarget {
      *
      * @private {shaka.util.Timer}
      */
-    this.filterTimer_ = new shaka.util.Timer(() => {
-      this.filterBySeekRange_();
-    }).tickEvery(
-        /* seconds= */ shaka.media.RegionTimeline.REGION_FILTER_INTERVAL);
+    this.filterTimer_ = null;
   }
 
   /** @override */
   release() {
     this.regions_.clear();
-    this.filterTimer_.stop();
+    this.releaseTimer_();
     super.release();
   }
 
   /**
    * @param {T} region
    */
   addRegion(region) {
-    const similarRegion = this.findSimilarRegion_(region);
+    const key = this.generateKey_(region);
 
     // Make sure we don't add duplicate regions. We keep track of this here
     // instead of making the parser track it.
-    if (similarRegion == null) {
-      this.regions_.add(region);
+    if (!this.regions_.has(key)) {
+      this.regions_.set(key, region);
       const event = new shaka.util.FakeEvent('regionadd', new Map([
         ['region', region],
       ]));
       this.dispatchEvent(event);
+      this.setupTimer_();
     }
   }
 
@@ -76,48 +74,42 @@ shaka.media.RegionTimeline = class extends shaka.util.FakeEventTarget {
    */
   filterBySeekRange_() {
     const seekRange = this.getSeekRange_();
-    for (const region of this.regions_) {
+    for (const [key, region] of this.regions_) {
       // Only consider the seek range start here.
       // Future regions might become relevant eventually,
       // but regions that are in the past and can't ever be
       // seeked to will never come up again, and there's no
       // reason to store or process them.
       if (region.endTime < seekRange.start) {
-        this.regions_.delete(region);
+        this.regions_.delete(key);
         const event = new shaka.util.FakeEvent('regionremove', new Map([
           ['region', region],
         ]));
         this.dispatchEvent(event);
       }
     }
+    if (!this.regions_.size) {
+      this.releaseTimer_();
+    }
   }
 
-  /**
-   * Find a region in the timeline that has the same scheme id uri, event id,
-   * start time and end time. If these four parameters match, we assume it
-   * to be the same region. If no similar region can be found, |null| will be
-   * returned.
-   *
-   * @param {T} region
-   * @return {?T}
-   * @private
-   */
-  findSimilarRegion_(region) {
-    const isDiffNegligible = (a, b) => Math.abs(a - b) < 0.1;
-    for (const existing of this.regions_) {
-      // The same scheme ID and time range means that it is similar-enough to
-      // be the same region.
-      const isSimilar = existing.schemeIdUri == region.schemeIdUri &&
-          existing.id == region.id &&
-          isDiffNegligible(existing.startTime, region.startTime) &&
-          isDiffNegligible(existing.endTime, region.endTime);
-
-      if (isSimilar) {
-        return existing;
-      }
+  /** @private */
+  setupTimer_() {
+    if (this.filterTimer_) {
+      return;
     }
+    this.filterTimer_ = new shaka.util.Timer(() => {
+      this.filterBySeekRange_();
+    }).tickEvery(
+        /* seconds= */ shaka.media.RegionTimeline.REGION_FILTER_INTERVAL);
+  }
 
-    return null;
+  /** @private */
+  releaseTimer_() {
+    if (this.filterTimer_) {
+      this.filterTimer_.stop();
+      this.filterTimer_ = null;
+    }
   }
 
   /**
@@ -128,7 +120,17 @@ shaka.media.RegionTimeline = class extends shaka.util.FakeEventTarget {
    * @return {!Iterable<T>}
    */
   regions() {
-    return this.regions_;
+    return this.regions_.values();
+  }
+
+  /**
+   * @param {T} region
+   * @return {string}
+   * @private
+   */
+  generateKey_(region) {
+    return `${region.schemeIdUri}_${region.id}_` +
+      `${region.startTime.toFixed(1)}_${region.endTime.toFixed(1)}`;
   }
 };