feat(HLS): Support byterange optimization on servers with support to …

…blocking playlist reload (shaka-project#5347)

Some servers only support blocking playlist reload for a short time
(example: 3 partial segment times). If we are using byte range
optimization we must change the reload time to be that of a complete
segment and avoid these problems.

lib/hls/hls_parser.js

@@ -212,6 +212,9 @@ shaka.hls.HlsParser = class {
 
     /** @private {boolean} */
     this.lowLatencyMode_ = false;
+
+    /** @private {boolean} */
+    this.lowLatencyByterangeOptimization_ = false;
   }
 
 
@@ -385,8 +388,6 @@ shaka.hls.HlsParser = class {
           shaka.util.Error.Code.HLS_INVALID_PLAYLIST_HIERARCHY);
     }
 
-    this.determineLastTargetDuration_(playlist);
-
     /** @type {!Array.<!shaka.hls.Tag>} */
     const variablesTags = shaka.hls.Utils.filterTagsByName(playlist.tags,
         'EXT-X-DEFINE');
@@ -446,6 +447,8 @@ shaka.hls.HlsParser = class {
       // until we've seen the ENDLIST tag for all active playlists.
       streamInfo.hasEndList = true;
     }
+
+    this.determineLastTargetDuration_(playlist);
   }
 
 
@@ -2265,6 +2268,10 @@ shaka.hls.HlsParser = class {
 
     this.determinePresentationType_(playlist);
 
+    if (this.isLive_()) {
+      this.determineLastTargetDuration_(playlist);
+    }
+
     if (!mimeType) {
       mimeType = await this.guessMimeType_(type, codecs, playlist,
           mediaVariables);
@@ -2282,14 +2289,12 @@ shaka.hls.HlsParser = class {
 
     const mediaSequenceToStartTime = this.isLive_() ?
         this.mediaSequenceToStartTimeByType_.get(type) : new Map();
-    const prevLowLatencyMode = this.lowLatencyMode_;
     const segments = this.createSegments_(verbatimMediaPlaylistUri, playlist,
         type, mimeType, mediaSequenceToStartTime, mediaVariables);
 
-    // This happens when autoLowLatencyMode is true, so we need set the
-    // correct lowLatencyPresentationDelay_
-    if (prevLowLatencyMode != this.lowLatencyMode_) {
-      this.determinePresentationType_(playlist);
+    // This new calculation is necessary for Low Latency streams.
+    if (this.isLive_()) {
+      this.determineLastTargetDuration_(playlist);
     }
 
     const firstStartTime = segments[0].startTime;
@@ -2609,8 +2614,6 @@ shaka.hls.HlsParser = class {
       } else {
         this.setPresentationType_(PresentationType.EVENT);
       }
-
-      this.determineLastTargetDuration_(playlist);
     }
   }
 
@@ -2620,11 +2623,34 @@ shaka.hls.HlsParser = class {
    * @private
    */
   determineLastTargetDuration_(playlist) {
+    let lastTargetDuration = Infinity;
+    const segments = playlist.segments;
+    if (segments.length) {
+      let segmentIndex = segments.length - 1;
+      while (segmentIndex >= 0) {
+        const segment = segments[segmentIndex];
+        const extinfTag =
+            shaka.hls.Utils.getFirstTagWithName(segment.tags, 'EXTINF');
+        if (extinfTag) {
+          // The EXTINF tag format is '#EXTINF:<duration>,[<title>]'.
+          // We're interested in the duration part.
+          const extinfValues = extinfTag.value.split(',');
+          lastTargetDuration = Number(extinfValues[0]);
+          break;
+        }
+        segmentIndex--;
+      }
+    }
+
     const targetDurationTag = this.getRequiredTag_(playlist.tags,
         'EXT-X-TARGETDURATION');
     const targetDuration = Number(targetDurationTag.value);
     const partialTargetDurationTag =
       shaka.hls.Utils.getFirstTagWithName(playlist.tags, 'EXT-X-PART-INF');
+    if (partialTargetDurationTag) {
+      this.partialTargetDuration_ = Number(
+          partialTargetDurationTag.getRequiredAttrValue('PART-TARGET'));
+    }
     // Get the server-recommended min distance from the live edge.
     const serverControlTag = shaka.hls.Utils.getFirstTagWithName(
         playlist.tags, 'EXT-X-SERVER-CONTROL');
@@ -2635,34 +2661,19 @@ shaka.hls.HlsParser = class {
     // targetDuration value across all playlists.
     // 1. Update the shortest one to use as update period and segment
     // availability time (for LIVE).
-    if (this.lowLatencyMode_ && partialTargetDurationTag) {
+    if (this.lowLatencyMode_ && this.partialTargetDuration_) {
       // For low latency streaming, use the partial segment target duration.
-      this.partialTargetDuration_ = Number(
-          partialTargetDurationTag.getRequiredAttrValue('PART-TARGET'));
-      this.lastTargetDuration_ = Math.min(
-          this.partialTargetDuration_, this.lastTargetDuration_);
+      if (this.lowLatencyByterangeOptimization_) {
+        this.lastTargetDuration_ = Math.min(
+            lastTargetDuration, this.lastTargetDuration_);
+      } else {
+        this.lastTargetDuration_ = Math.min(
+            this.partialTargetDuration_, this.lastTargetDuration_);
+      }
       // Use 'PART-HOLD-BACK' as the presentation delay for low latency mode.
       this.lowLatencyPresentationDelay_ = serverControlTag ? Number(
           serverControlTag.getRequiredAttrValue('PART-HOLD-BACK')) : 0;
     } else {
-      let lastTargetDuration = Infinity;
-      const segments = playlist.segments;
-      if (segments.length) {
-        let segmentIndex = segments.length - 1;
-        while (segmentIndex >= 0) {
-          const segment = segments[segmentIndex];
-          const extinfTag =
-              shaka.hls.Utils.getFirstTagWithName(segment.tags, 'EXTINF');
-          if (extinfTag) {
-            // The EXTINF tag format is '#EXTINF:<duration>,[<title>]'.
-            // We're interested in the duration part.
-            const extinfValues = extinfTag.value.split(',');
-            lastTargetDuration = Number(extinfValues[0]);
-            break;
-          }
-          segmentIndex--;
-        }
-      }
       this.lastTargetDuration_ = Math.min(
           lastTargetDuration, this.lastTargetDuration_);
       // Use 'HOLD-BACK' as the presentation delay for default if defined.
@@ -3047,6 +3058,7 @@ shaka.hls.HlsParser = class {
     );
 
     if (segmentWithByteRangeOptimization) {
+      this.lowLatencyByterangeOptimization_ = true;
       reference.markAsByterangeOptimization();
 
       if (isPreloadSegment) {