fix(dash): Fix performance regression

Author: Alvaro Velad

lib/dash/dash_parser.js

@@ -22,7 +22,6 @@ goog.require('shaka.text.TextEngine');
 goog.require('shaka.util.CmcdManager');
 goog.require('shaka.util.Error');
 goog.require('shaka.util.Functional');
-goog.require('shaka.util.Iterables');
 goog.require('shaka.util.LanguageUtils');
 goog.require('shaka.util.ManifestParserUtils');
 goog.require('shaka.util.MimeUtils');
@@ -104,7 +103,7 @@ shaka.dash.DashParser = class {
 
     /**
      * Period IDs seen in previous manifest.
-     * @private {!Array.<number>}
+     * @private {!Array.<string>}
      */
     this.lastManifestUpdatePeriodIds_ = [];
 
@@ -556,23 +555,22 @@ shaka.dash.DashParser = class {
     const periods = [];
     let prevEnd = 0;
     const periodNodes = XmlUtils.findChildren(mpd, 'Period');
-    // This uses a for-loop rather than a for-of loop because this needs to look
-    // ahead to the next element.
-    const enumerate = (it) => shaka.util.Iterables.enumerate(it);
-    for (const {i, item: elem, next} of enumerate(periodNodes)) {
+    for (let i = 0; i < periodNodes.length; i++) {
+      const elem = periodNodes[i];
       const start = /** @type {number} */ (
         XmlUtils.parseAttr(elem, 'start', XmlUtils.parseDuration, prevEnd));
       const periodId = elem.id;
       const givenDuration =
           XmlUtils.parseAttr(elem, 'duration', XmlUtils.parseDuration);
 
       let periodDuration = null;
-      if (next) {
+      if (i + 1 < periodNodes.length) {
+        const nextPeriod = periodNodes[i + 1];
         // "The difference between the start time of a Period and the start time
         // of the following Period is the duration of the media content
         // represented by this Period."
         const nextStart =
-            XmlUtils.parseAttr(next, 'start', XmlUtils.parseDuration);
+            XmlUtils.parseAttr(nextPeriod, 'start', XmlUtils.parseDuration);
         if (nextStart != null) {
           periodDuration = nextStart - start;
         }
@@ -637,7 +635,7 @@ shaka.dash.DashParser = class {
         start: start,
         duration: periodDuration,
         node: elem,
-        isLastPeriod: periodDuration == null || !next,
+        isLastPeriod: periodDuration == null || (i + 1 == periodNodes.length),
       };
       const period = this.parsePeriod_(context, baseUris, info);
       periods.push(period);
@@ -647,12 +645,12 @@ shaka.dash.DashParser = class {
       }
 
       if (periodDuration == null) {
-        if (next) {
+        if (i + 1 < periodNodes.length) {
           // If the duration is still null and we aren't at the end, then we
           // will skip any remaining periods.
           shaka.log.warning(
               'Skipping Period', i + 1, 'and any subsequent Periods:', 'Period',
-              i + 1, 'does not have a valid start time.', next);
+              i + 1, 'does not have a valid start time.', periodNodes[i + 1]);
         }
 
         // The duration is unknown, so the end is unknown.

lib/dash/mpd_utils.js

@@ -142,8 +142,8 @@ shaka.dash.MpdUtils = class {
     const timeline = [];
     let lastEndTime = -unscaledPresentationTimeOffset;
 
-    const enumerate = (it) => shaka.util.Iterables.enumerate(it);
-    for (const {item: timePoint, next} of enumerate(timePoints)) {
+    for (let i = 0; i < timePoints.length; ++i) {
+      const timePoint = timePoints[i];
       let t = XmlUtils.parseAttr(timePoint, 't', XmlUtils.parseNonNegativeInt);
       const d =
           XmlUtils.parseAttr(timePoint, 'd', XmlUtils.parseNonNegativeInt);
@@ -165,9 +165,10 @@ shaka.dash.MpdUtils = class {
 
       let repeat = r || 0;
       if (repeat < 0) {
-        if (next) {
-          const nextStartTime =
-              XmlUtils.parseAttr(next, 't', XmlUtils.parseNonNegativeInt);
+        if (i + 1 < timePoints.length) {
+          const nextTimePoint = timePoints[i + 1];
+          const nextStartTime = XmlUtils.parseAttr(
+              nextTimePoint, 't', XmlUtils.parseNonNegativeInt);
           if (nextStartTime == null) {
             shaka.log.warning(
                 'An "S" element cannot have a negative repeat',

lib/dash/segment_template.js

@@ -14,7 +14,6 @@ goog.require('shaka.media.InitSegmentReference');
 goog.require('shaka.media.SegmentIndex');
 goog.require('shaka.media.SegmentReference');
 goog.require('shaka.util.Error');
-goog.require('shaka.util.Iterables');
 goog.require('shaka.util.ManifestParserUtils');
 goog.require('shaka.util.ObjectUtils');
 goog.requireType('shaka.dash.DashParser');
@@ -504,8 +503,11 @@ shaka.dash.SegmentTemplate = class {
 
     /** @type {!Array.<!shaka.media.SegmentReference>} */
     const references = [];
-    const enum_ = (it) => shaka.util.Iterables.enumerate(it);
-    for (const {i, item: {start, unscaledStart, end}} of enum_(info.timeline)) {
+    for (let i = 0; i < info.timeline.length; i++) {
+      const start = info.timeline[i].start;
+      const unscaledStart = info.timeline[i].unscaledStart;
+      const end = info.timeline[i].end;
+
       // Note: i = k - 1, where k indicates the k'th segment listed in the MPD.
       // (See section 5.3.9.5.3 of the DASH spec.)
       const segmentReplacement = i + info.startNumber;

lib/util/string_utils.js

@@ -158,9 +158,8 @@ shaka.util.StringUtils = class {
   static toUTF16(str, littleEndian) {
     const result = new ArrayBuffer(str.length * 2);
     const view = new DataView(result);
-    const enumerate = (it) => shaka.util.Iterables.enumerate(it);
-    for (const {i, item} of enumerate(str)) {
-      const value = item.charCodeAt(0);
+    for (let i = 0; i < str.length; ++i) {
+      const value = str.charCodeAt(i);
       view.setUint16(/* position= */ i * 2, value, littleEndian);
     }
     return result;

lib/util/uint8array_utils.js

@@ -74,9 +74,8 @@ shaka.util.Uint8ArrayUtils = class {
     // byte.
     const bytes = window.atob(str.replace(/-/g, '+').replace(/_/g, '/'));
     const result = new Uint8Array(bytes.length);
-    const enumerate = (it) => shaka.util.Iterables.enumerate(it);
-    for (const {i, item} of enumerate(bytes)) {
-      result[i] = item.charCodeAt(0);
+    for (let i = 0; i < bytes.length; ++i) {
+      result[i] = bytes.charCodeAt(i);
     }
     return result;
   }