Remove position from SegmentReference

As part of Period-flattening, I'm trying to remove our dependence on the "position" field of SegmentReference. With that eliminated, we can more easily concatenate Arrays of SegmentReferences without modifying them. - Make SegmentIndex iterable - Add specialized seek() and current() methods to SegmentIterator - Remove position from SegmentReference - Make positions in SegmentIndex API stable without field in reference - Remove brittle hard-coded positions in tests (except SegmentIndex tests, where they would be hard to avoid in testing methods separately) - Use SegmentIterator in StreamingEngine to track the next segment between switches Issue #892 (refactor StreamingEngine) Issue #1339 (period flattening) Change-Id: I666cc21249c34ee6cbc138a59109d9f1159fa127
shaka-project · Mar 23, 2020 · 1ab3f9c · 1ab3f9c
1 parent 6202b93
commit 1ab3f9c
Show file tree

Hide file tree

Showing 32 changed files with 639 additions and 515 deletions.
diff --git a/build/eslint-plugin-shaka-rules/private.js b/build/eslint-plugin-shaka-rules/private.js
@@ -68,7 +68,7 @@ module.exports = {
     return {
       'ClassBody > MethodDefinition': (node) => {
         const comment = source.getCommentsBefore(node).pop();
-        const nameIsPrivate = node.key.name.endsWith('_');
+        const nameIsPrivate = node.key.name && node.key.name.endsWith('_');
         if (!comment) {
           if (nameIsPrivate) {
             ctx.report({

diff --git a/docs/tutorials/manifest-parser.md b/docs/tutorials/manifest-parser.md
@@ -177,13 +177,12 @@ It handles merging new segments, and expanding the list of segments for live
 streams.
 
 ```js
-var references = refs.map(function(r, position) {
+var references = refs.map(function(r) {
   // Should return an array of possible URI choices; this is used for failover
   // in the event of network error.  This is a function to defer calculations.
   var getUris = function() { return [r.uri]; };
 
   return new shaka.media.SegmentReference(
-      position,
       r.start, r.end, getUris,
       /* startByte */ 0,
       /* endByte */ null,
@@ -329,7 +328,7 @@ MyManifestParser.prototype.loadReference_ =
     function(position, start, end, initSegmentReference) {
   var getUris = function() { return ['https://example.com/ref_' + position]; };
   return new shaka.media.SegmentReference(
-      position, start, end, getUris,
+      start, end, getUris,
       /* startByte */ 0,
       /* endByte */ null,
       initSegmentReference,

diff --git a/lib/dash/segment_list.js b/lib/dash/segment_list.js
@@ -236,7 +236,6 @@ shaka.dash.SegmentList = class {
       const getUris = () => mediaUri;
       references.push(
           new shaka.media.SegmentReference(
-              i + startNumber,
               periodStart + startTime,
               periodStart + endTime,
               getUris,

diff --git a/lib/dash/segment_template.js b/lib/dash/segment_template.js
@@ -376,7 +376,6 @@ shaka.dash.SegmentTemplate = class {
           'Generated a segment outside of the period!');
 
       return new shaka.media.SegmentReference(
-          position,
           segmentStart,
           segmentEnd,
           getUris,
@@ -471,7 +470,6 @@ shaka.dash.SegmentTemplate = class {
           };
 
       references.push(new shaka.media.SegmentReference(
-          segmentReplacement,
           periodStart + start,
           periodStart + end,
           createUris,

diff --git a/lib/hls/hls_parser.js b/lib/hls/hls_parser.js
@@ -1422,7 +1422,6 @@ shaka.hls.HlsParser = class {
     }
 
     return new shaka.media.SegmentReference(
-        position,
         startTime,
         endTime,
         () => [absoluteSegmentUri],

diff --git a/lib/media/mp4_segment_index_parser.js b/lib/media/mp4_segment_index_parser.js
@@ -151,7 +151,6 @@ shaka.media.Mp4SegmentIndexParser = class {
 
       references.push(
           new shaka.media.SegmentReference(
-              references.length,
               nativeStartTime + timestampOffset,
               nativeEndTime + timestampOffset,
               (() => { return uris; }),

diff --git a/lib/media/segment_index.js b/lib/media/segment_index.js
@@ -4,6 +4,7 @@
  */
 
 goog.provide('shaka.media.SegmentIndex');
+goog.provide('shaka.media.SegmentIterator');
 
 goog.require('goog.asserts');
 goog.require('shaka.media.SegmentReference');
@@ -15,14 +16,14 @@ goog.require('shaka.util.Timer');
  * SegmentIndex.
  *
  * @implements {shaka.util.IDestroyable}
+ * @implements {Iterable.<!shaka.media.SegmentReference>}
  * @export
  */
 shaka.media.SegmentIndex = class {
   /**
    * @param {!Array.<!shaka.media.SegmentReference>} references The list of
    *   SegmentReferences, which must be sorted first by their start times
-   *   (ascending) and second by their end times (ascending).  They must have
-   *   continuous, increasing positions.
+   *   (ascending) and second by their end times (ascending).
    */
   constructor(references) {
     if (goog.DEBUG) {
@@ -34,6 +35,14 @@ shaka.media.SegmentIndex = class {
 
     /** @private {shaka.util.Timer} */
     this.timer_ = null;
+
+    /**
+     * The number of references that have been removed from the front of the
+     * array.  Used to create stable positions in the find/get APIs.
+     *
+     * @private {number}
+     */
+    this.numEvicted_ = 0;
   }
 
 
@@ -60,8 +69,8 @@ shaka.media.SegmentIndex = class {
    * time.
    *
    * @param {number} time
-   * @return {?number} The position of the segment, or null
-   *   if the position of the segment could not be determined.
+   * @return {?number} The position of the segment, or null if the position of
+   *   the segment could not be determined.
    * @export
    */
   find(time) {
@@ -72,11 +81,11 @@ shaka.media.SegmentIndex = class {
       const r = this.references_[i];
       // Note that a segment ends immediately before the end time.
       if ((time >= r.startTime) && (time < r.endTime)) {
-        return r.position;
+        return i + this.numEvicted_;
       }
     }
     if (this.references_.length && time < this.references_[0].startTime) {
-      return this.references_[0].position;
+      return this.numEvicted_;
     }
 
     return null;
@@ -86,7 +95,7 @@ shaka.media.SegmentIndex = class {
   /**
    * Gets the SegmentReference for the segment at the given position.
    *
-   * @param {number} position The position of the segment.
+   * @param {number} position The position of the segment as returned by find().
    * @return {shaka.media.SegmentReference} The SegmentReference, or null if
    *   no such SegmentReference exists.
    * @export
@@ -96,7 +105,7 @@ shaka.media.SegmentIndex = class {
       return null;
     }
 
-    const index = position - this.references_[0].position;
+    const index = position - this.numEvicted_;
     if (index < 0 || index >= this.references_.length) {
       return null;
     }
@@ -127,8 +136,7 @@ shaka.media.SegmentIndex = class {
    *
    * @param {!Array.<!shaka.media.SegmentReference>} references The list of
    *   SegmentReferences, which must be sorted first by their start times
-   *   (ascending) and second by their end times (ascending).  They must have
-   *   continuous, increasing positions.
+   *   (ascending) and second by their end times (ascending).
    * @export
    */
   merge(references) {
@@ -188,7 +196,16 @@ shaka.media.SegmentIndex = class {
    * @export
    */
   evict(time) {
+    const oldSize = this.references_.length;
+
     this.references_ = this.references_.filter((ref) => ref.endTime > time);
+
+    const newSize = this.references_.length;
+    const diff = oldSize - newSize;
+
+    // Tracking the number of evicted refs will keep their "positions" stable
+    // for the caller.
+    this.numEvicted_ += diff;
   }
 
 
@@ -224,6 +241,7 @@ shaka.media.SegmentIndex = class {
       const firstReference = this.references_[0];
       if (firstReference.endTime <= periodStart) {
         this.references_.shift();
+        this.numEvicted_++;
       } else {
         break;
       }
@@ -237,7 +255,6 @@ shaka.media.SegmentIndex = class {
     const lastReference = this.references_[this.references_.length - 1];
     this.references_[this.references_.length - 1] =
         new shaka.media.SegmentReference(
-            lastReference.position,
             lastReference.startTime,
             /* endTime= */ periodEnd,
             lastReference.getUris,
@@ -272,6 +289,12 @@ shaka.media.SegmentIndex = class {
   }
 
 
+  /** @return {!shaka.media.SegmentIterator} */
+  [Symbol.iterator]() {
+    return new shaka.media.SegmentIterator(this);
+  }
+
+
   /**
    * Create a SegmentIndex for a single segment of the given start time and
    * duration at the given URIs.
@@ -284,7 +307,6 @@ shaka.media.SegmentIndex = class {
    */
   static forSingleSegment(startTime, duration, uris) {
     const reference = new shaka.media.SegmentReference(
-        /* position= */ 1,
         /* startTime= */ startTime,
         /* endTime= */ startTime + duration,
         /* getUris= */ () => uris,
@@ -301,8 +323,7 @@ shaka.media.SegmentIndex = class {
 
 if (goog.DEBUG) {
   /**
-   * Asserts that the given SegmentReferences are sorted and have continuous,
-   * increasing positions.
+   * Asserts that the given SegmentReferences are sorted.
    *
    * @param {!Array.<shaka.media.SegmentReference>} references
    * @private
@@ -313,9 +334,6 @@ if (goog.DEBUG) {
         return true;
       }
       const r1 = references[i - 1];
-      if (r2.position != r1.position + 1) {
-        return false;
-      }
       if (r1.startTime < r2.startTime) {
         return true;
       } else if (r1.startTime > r2.startTime) {
@@ -331,3 +349,61 @@ if (goog.DEBUG) {
   };
 }
 
+
+/**
+ * An iterator over a SegmentIndex's references.
+ *
+ * @implements {Iterator.<shaka.media.SegmentReference>}
+ * @export
+ */
+shaka.media.SegmentIterator = class {
+  /** @param {shaka.media.SegmentIndex} segmentIndex */
+  constructor(segmentIndex) {
+    /** @private {shaka.media.SegmentIndex} */
+    this.segmentIndex_ = segmentIndex;
+
+    /** @private {number} */
+    this.nextPosition_ = 0;
+  }
+
+  /**
+   * Move the iterator to a given timestamp in the underlying SegmentIndex.
+   *
+   * @param {number} time
+   * @return {shaka.media.SegmentReference}
+   * @export
+   */
+  seek(time) {
+    const position = this.segmentIndex_.find(time);
+    if (position == null) {
+      // An arbitrary, large number whose position will not find anything in the
+      // segment index, even when incremented.
+      this.nextPosition_ = 2**31;
+      return null;
+    }
+
+    this.nextPosition_ = position;
+    // Post-increment so that next() returns the one after this.
+    return this.segmentIndex_.get(this.nextPosition_++);
+  }
+
+  /**
+   * @return {shaka.media.SegmentReference}
+   * @export
+   */
+  current() {
+    return this.segmentIndex_.get(this.nextPosition_ - 1);
+  }
+
+  /**
+   * @override
+   * @export
+   */
+  next() {
+    const ref = this.segmentIndex_.get(this.nextPosition_++);
+    return {
+      'value': ref,
+      'done': !ref,
+    };
+  }
+};
diff --git a/lib/media/segment_reference.js b/lib/media/segment_reference.js
@@ -81,12 +81,6 @@ shaka.media.InitSegmentReference = class {
  */
 shaka.media.SegmentReference = class {
   /**
-   * @param {number} position The segment's position.
-   *   The following should hold true between any two SegmentReferences r1 and
-   *   r2:
-   *   IF r2.position > r1.position THEN
-   *     [ (r2.startTime > r1.startTime) OR
-   *       (r2.startTime == r1.startTime AND r2.endTime >= r1.endTime) ]
    * @param {number} startTime The segment's start time in seconds.
    * @param {number} endTime The segment's end time in seconds.  The segment
    *   ends the instant before this time, so |endTime| must be strictly greater
@@ -123,17 +117,13 @@ shaka.media.SegmentReference = class {
    *   MediaSource.
    */
   constructor(
-      position, startTime, endTime, uris, startByte, endByte,
-      initSegmentReference, timestampOffset, appendWindowStart,
-      appendWindowEnd) {
+      startTime, endTime, uris, startByte, endByte, initSegmentReference,
+      timestampOffset, appendWindowStart, appendWindowEnd) {
     goog.asserts.assert(startTime < endTime,
         'startTime must be less than endTime');
     goog.asserts.assert((startByte < endByte) || (endByte == null),
         'startByte must be < endByte');
 
-    /** @const {number} */
-    this.position = position;
-
     /** @type {number} */
     this.startTime = startTime;
 
@@ -162,16 +152,6 @@ shaka.media.SegmentReference = class {
     this.appendWindowEnd = appendWindowEnd;
   }
 
-  /**
-   * Returns the segment's position.
-   *
-   * @return {number} The segment's position.
-   * @export
-   */
-  getPosition() {
-    return this.position;
-  }
-
   /**
    * Returns the segment's start time in seconds.
    *