fix(HLS): Allow sync live streams without PROGRAM-DATE-TIME (#7340)

Author: avelad

lib/hls/hls_parser.js

@@ -152,6 +152,14 @@ shaka.hls.HlsParser = class {
      */
     this.lowestSyncTime_ = Infinity;
 
+    /**
+     * Flag to indicate if any of the media playlists use
+     * EXT-X-PROGRAM-DATE-TIME.
+     *
+     * @private {boolean}
+     */
+    this.usesProgramDateTime_ = false;
+
     /**
      * Whether the streams have previously been "finalized"; that is to say,
      * whether we have loaded enough streams to know information about the asset
@@ -621,9 +629,10 @@ shaka.hls.HlsParser = class {
    * Align the streams by sequence number by dropping early segments.  Then
    * offset the streams to begin at presentation time 0.
    * @param {!Array.<!shaka.hls.HlsParser.StreamInfo>} streamInfos
+   * @param {boolean=} force
    * @private
    */
-  syncStreamsWithSequenceNumber_(streamInfos) {
+  syncStreamsWithSequenceNumber_(streamInfos, force = false) {
     // We assume that, when this is first called, we have enough info to
     // determine how to use the program date times (e.g. we have both a video
     // and an audio, and all other videos and audios match those).
@@ -678,7 +687,7 @@ shaka.hls.HlsParser = class {
         this.minSequenceNumber_);
 
     for (const streamInfo of streamInfos) {
-      if (!this.ignoreManifestProgramDateTimeFor_(streamInfo.type)) {
+      if (!this.ignoreManifestProgramDateTimeFor_(streamInfo.type) && !force) {
         continue;
       }
       const segmentIndex = streamInfo.stream.segmentIndex;
@@ -2752,8 +2761,12 @@ shaka.hls.HlsParser = class {
       }
     }
     this.notifySegmentsForStreams_(streamInfos.map((s) => s.stream));
-    if (this.config_.hls.ignoreManifestProgramDateTime) {
-      this.syncStreamsWithSequenceNumber_(streamInfos);
+    const liveWithNoProgramaDateTime =
+        this.isLive_() && !this.usesProgramDateTime_;
+    if (this.config_.hls.ignoreManifestProgramDateTime ||
+        liveWithNoProgramaDateTime) {
+      this.syncStreamsWithSequenceNumber_(
+          streamInfos, liveWithNoProgramaDateTime);
     } else {
       this.syncStreamsWithProgramDateTime_(streamInfos);
       if (this.config_.hls.ignoreManifestProgramDateTimeForTypes.length > 0) {
@@ -3626,6 +3639,7 @@ shaka.hls.HlsParser = class {
         syncTime = shaka.util.TXml.parseDate(dateTimeTag.value);
         goog.asserts.assert(syncTime != null,
             'EXT-X-PROGRAM-DATE-TIME format not valid');
+        this.usesProgramDateTime_ = true;
       }
     }