From 3b0f01377f526a42662c2ff4843d49f860f44bea Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Wojciech=20Tyczy=C5=84ski?= <wojciech.tyczynski@sky.uk>
Date: Wed, 19 Apr 2023 19:03:07 +0200
Subject: [PATCH] fix(DASH): Fix seeking on multiperiod content after variant
 change (#5110)

Fixes an issue where `createSegmentIndex()` creates a reference in
cached Stream and not on a new Stream. Now cached value is reused in
period flattening.

Updated assertion in Period Combiner to catch potential issues within
old approach.

Without this fix I've noticed problems around seeking on multiperiod
content after variant change.
---
 lib/dash/dash_parser.js | 97 +++++++++++++++++++++--------------------
 lib/util/periods.js     |  8 ++--
 2 files changed, 53 insertions(+), 52 deletions(-)

diff --git a/lib/dash/dash_parser.js b/lib/dash/dash_parser.js
index 69c07c091c..ce4b20578e 100644
--- a/lib/dash/dash_parser.js
+++ b/lib/dash/dash_parser.js
@@ -1277,55 +1277,56 @@ shaka.dash.DashParser = class {
         context.period.id + ',' + context.representation.id : '';
 
     /** @type {shaka.extern.Stream} */
-    const stream = {
-      id: this.globalId_++,
-      originalId: context.representation.id,
-      createSegmentIndex: async () => {
-        // If we have a stream with the same context id stored in the map
-        // that has no segmentIndex, we should set the segmentIndex for it.
-        const storedInMap = contextId && context.dynamic &&
-              this.streamMap_[contextId];
-
-        const currentStream = storedInMap ? this.streamMap_[contextId] : stream;
-        if (!currentStream.segmentIndex) {
-          currentStream.segmentIndex = await streamInfo.generateSegmentIndex();
-        }
-      },
+    let stream;
 
-      closeSegmentIndex: () => {
-        if (stream.segmentIndex) {
-          stream.segmentIndex.release();
-          stream.segmentIndex = null;
-        }
-      },
-      segmentIndex: null,
-      mimeType: context.representation.mimeType,
-      codecs: context.representation.codecs,
-      frameRate: context.representation.frameRate,
-      pixelAspectRatio: context.representation.pixelAspectRatio,
-      bandwidth: context.bandwidth,
-      width: context.representation.width,
-      height: context.representation.height,
-      kind,
-      encrypted: contentProtection.drmInfos.length > 0,
-      drmInfos: contentProtection.drmInfos,
-      keyIds,
-      language,
-      label,
-      type: context.adaptationSet.contentType,
-      primary: isPrimary,
-      trickModeVideo: null,
-      emsgSchemeIdUris:
-          context.representation.emsgSchemeIdUris,
-      roles,
-      forced: forced,
-      channelsCount: context.representation.numChannels,
-      audioSamplingRate: context.representation.audioSamplingRate,
-      spatialAudio: spatialAudio,
-      closedCaptions,
-      hdr,
-      tilesLayout,
-      matchedStreams: [],
+    if (contextId && this.streamMap_[contextId]) {
+      stream = this.streamMap_[contextId];
+    } else {
+      stream = {
+        id: this.globalId_++,
+        originalId: context.representation.id,
+        createSegmentIndex: () => Promise.resolve(),
+        closeSegmentIndex: () => {
+          if (stream.segmentIndex) {
+            stream.segmentIndex.release();
+            stream.segmentIndex = null;
+          }
+        },
+        segmentIndex: null,
+        mimeType: context.representation.mimeType,
+        codecs: context.representation.codecs,
+        frameRate: context.representation.frameRate,
+        pixelAspectRatio: context.representation.pixelAspectRatio,
+        bandwidth: context.bandwidth,
+        width: context.representation.width,
+        height: context.representation.height,
+        kind,
+        encrypted: contentProtection.drmInfos.length > 0,
+        drmInfos: contentProtection.drmInfos,
+        keyIds,
+        language,
+        label,
+        type: context.adaptationSet.contentType,
+        primary: isPrimary,
+        trickModeVideo: null,
+        emsgSchemeIdUris:
+            context.representation.emsgSchemeIdUris,
+        roles,
+        forced,
+        channelsCount: context.representation.numChannels,
+        audioSamplingRate: context.representation.audioSamplingRate,
+        spatialAudio,
+        closedCaptions,
+        hdr,
+        tilesLayout,
+        matchedStreams: [],
+      };
+    }
+
+    stream.createSegmentIndex = async () => {
+      if (!stream.segmentIndex) {
+        stream.segmentIndex = await streamInfo.generateSegmentIndex();
+      }
     };
 
     if (contextId && context.dynamic && !this.streamMap_[contextId]) {
diff --git a/lib/util/periods.js b/lib/util/periods.js
index e6cbe620b0..e5b9072ab6 100644
--- a/lib/util/periods.js
+++ b/lib/util/periods.js
@@ -673,11 +673,11 @@ shaka.util.PeriodCombiner = class {
     // Also checks if the segmentIndex is still valid after the async
     // operations, to make sure we stop if the active stream has changed.
     if (outputStream.segmentIndex instanceof shaka.media.MetaSegmentIndex) {
-      for (let i = 0; i < streams.length; i++) {
+      for (let i = firstNewPeriodIndex; i < streams.length; i++) {
         const match = streams[i];
-        if (match.segmentIndex && i >= firstNewPeriodIndex) {
-          goog.asserts.assert(match.segmentIndex,
-              'stream should have a segmentIndex.');
+        goog.asserts.assert(match.segmentIndex,
+            'stream should have a segmentIndex.');
+        if (match.segmentIndex) {
           outputStream.segmentIndex.appendSegmentIndex(match.segmentIndex);
         }
       }