fix(hls): Handle unaligned HLS streams on VOD

This reverts the HLS parser to using per-stream mediaSequenceToStartTime
values for VOD, which will allow us to play unaligned HLS streams on
that sort of content.

Issue shaka-project#4308

lib/hls/hls_parser.js

@@ -76,6 +76,8 @@ shaka.hls.HlsParser = class {
      * that each stream of a type (video, audio, etc) has the same mappings of
      * sequence number to start time.
      * This map stores those relationships.
+     * Only used during livestreams; we do not assume that VOD content is
+     * synchronized in that way.
      * @private {!Map.<string, !Map.<number, number>>}
      */
     this.mediaSequenceToStartTimeByType_ = new Map();
@@ -313,6 +315,19 @@ shaka.hls.HlsParser = class {
     }
   }
 
+  /**
+   * @param {!shaka.hls.HlsParser.StreamInfo} streamInfo
+   * @return {!Map.<number, number>}
+   * @private
+   */
+  getMediaSequenceToStartTimeFor_(streamInfo) {
+    if (this.isLive_()) {
+      return this.mediaSequenceToStartTimeByType_.get(streamInfo.type);
+    } else {
+      return streamInfo.mediaSequenceToStartTime;
+    }
+  }
+
   /**
    * Updates a stream.
    *
@@ -350,7 +365,7 @@ shaka.hls.HlsParser = class {
     const stream = streamInfo.stream;
 
     const mediaSequenceToStartTime =
-        this.mediaSequenceToStartTimeByType_.get(streamInfo.type);
+        this.getMediaSequenceToStartTimeFor_(streamInfo);
     const segments = this.createSegments_(
         streamInfo.verbatimMediaPlaylistUri, playlist, stream.type,
         stream.mimeType, mediaSequenceToStartTime, mediaVariables);
@@ -410,7 +425,7 @@ shaka.hls.HlsParser = class {
       goog.asserts.assert(segmentIndex,
           'Only loaded streams should be synced');
       const mediaSequenceToStartTime =
-          this.mediaSequenceToStartTimeByType_.get(streamInfo.type);
+          this.getMediaSequenceToStartTimeFor_(streamInfo);
       const segment0 = segmentIndex.earliestReference();
       if (segment0) {
         // This looks inefficient, but iteration order is insertion order.
@@ -533,7 +548,7 @@ shaka.hls.HlsParser = class {
         'Negative maxTimestamp after adjustment!');
 
     const mediaSequenceToStartTime =
-        this.mediaSequenceToStartTimeByType_.get(streamInfo.type);
+        this.getMediaSequenceToStartTimeFor_(streamInfo);
     for (const [key, value] of mediaSequenceToStartTime) {
       mediaSequenceToStartTime.set(key, value + offset);
     }
@@ -1524,6 +1539,7 @@ shaka.hls.HlsParser = class {
       // These values are filled out or updated after lazy-loading:
       absoluteMediaPlaylistUri: initialMediaPlaylistUri,
       maxTimestamp: 0,
+      mediaSequenceToStartTime: new Map(),
       canSkipSegments: false,
       hasEndList: false,
       firstSequenceNumber: -1,
@@ -1565,6 +1581,8 @@ shaka.hls.HlsParser = class {
       streamInfo.maxTimestamp = realStreamInfo.maxTimestamp;
       streamInfo.canSkipSegments = realStreamInfo.canSkipSegments;
       streamInfo.hasEndList = realStreamInfo.hasEndList;
+      streamInfo.mediaSequenceToStartTime =
+          realStreamInfo.mediaSequenceToStartTime;
       stream.segmentIndex = realStream.segmentIndex;
       stream.encrypted = realStream.encrypted;
       stream.drmInfos = realStream.drmInfos;
@@ -1793,8 +1811,8 @@ shaka.hls.HlsParser = class {
           shaka.util.Error.Code.HLS_KEYFORMATS_NOT_SUPPORTED);
     }
 
-    const mediaSequenceToStartTime =
-        this.mediaSequenceToStartTimeByType_.get(type);
+    const mediaSequenceToStartTime = this.isLive_() ?
+        this.mediaSequenceToStartTimeByType_.get(type) : new Map();
     const segments = this.createSegments_(verbatimMediaPlaylistUri, playlist,
         type, mimeType, mediaSequenceToStartTime, mediaVariables);
 
@@ -1836,6 +1854,7 @@ shaka.hls.HlsParser = class {
       canSkipSegments,
       hasEndList: false,
       firstSequenceNumber: -1,
+      mediaSequenceToStartTime,
     };
   }
 
@@ -2981,6 +3000,7 @@ shaka.hls.HlsParser = class {
  *   verbatimMediaPlaylistUri: string,
  *   absoluteMediaPlaylistUri: string,
  *   maxTimestamp: number,
+ *   mediaSequenceToStartTime: !Map.<number, number>,
  *   canSkipSegments: boolean,
  *   hasEndList: boolean,
  *   firstSequenceNumber: number
@@ -3003,6 +3023,9 @@ shaka.hls.HlsParser = class {
  *   and updated to reflect any redirects.
  * @property {number} maxTimestamp
  *   The maximum timestamp found in the stream.
+ * @property {!Map.<number, number>} mediaSequenceToStartTime
+ *   A map of media sequence numbers to media start times.
+ *   Only used for VOD content.
  * @property {boolean} canSkipSegments
  *  True if the server supports delta playlist updates, and we can send a
  *  request for a playlist that can skip older media segments.