From 62f24d22491353bf3a37f451c74a26b77f892197 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?=C3=81lvaro=20Velad=20Galv=C3=A1n?= <ladvan91@hotmail.com>
Date: Mon, 12 Jun 2023 18:13:30 +0200
Subject: [PATCH] feat: Set segmentPrefetchLimit to 2 by default for low
 latency streaming (#5275)

---
 docs/tutorials/config.md         | 12 +++++++-----
 lib/player.js                    |  8 ++++++--
 lib/util/player_configuration.js |  2 ++
 test/player_unit.js              |  8 ++++++--
 4 files changed, 21 insertions(+), 9 deletions(-)

diff --git a/docs/tutorials/config.md b/docs/tutorials/config.md
index b147be4cc1..3d94cc5392 100644
--- a/docs/tutorials/config.md
+++ b/docs/tutorials/config.md
@@ -122,18 +122,20 @@ buffering settings) while some will not have any effect until the next call to
 #### Low latency streaming
 
 With `.streaming.lowLatencyMode` set to true,
-`.streaming.inaccurateManifestTolerance` is set to 0 by default, and
-`.streaming.rebufferingGoal` is set to 0.01 by default.
+`.streaming.inaccurateManifestTolerance` is set to 0 by default,
+`.streaming.rebufferingGoal` is set to 0.01 by default, and
+`.streaming.segmentPrefetchLimit` is set to 2 by default.
 
-To customize the values of inaccurateManifestTolerance and rebufferingGoal
-with low latency mode, you can set the fields in the same or subsequent
-call to configure().
+To customize the values of inaccurateManifestTolerance, rebufferingGoal and
+segmentPrefetchLimit with low latency mode, you can set the fields in the same
+or subsequent call to configure().
 ```js
 player.configure({
   streaming: {
     lowLatencyMode: true,
     inaccurateManifestTolerance: 0,
     rebufferingGoal: 0.01,
+    segmentPrefetchLimit: 2,
   }
 });
 
diff --git a/lib/player.js b/lib/player.js
index d704cd5eb9..67adda8146 100644
--- a/lib/player.js
+++ b/lib/player.js
@@ -3205,8 +3205,9 @@ shaka.Player = class extends shaka.util.FakeEventTarget {
     }
 
     // If lowLatencyMode is enabled, and inaccurateManifestTolerance and
-    // rebufferingGoal are not specified, set inaccurateManifestTolerance to 0
-    // and rebufferingGoal to 0.01 by default for low latency streaming.
+    // rebufferingGoal and segmentPrefetchLimit are not specified, set
+    // inaccurateManifestTolerance to 0 and rebufferingGoal to 0.01 and
+    // segmentPrefetchLimit to 2 by default for low latency streaming.
     if (config['streaming'] && config['streaming']['lowLatencyMode']) {
       if (config['streaming']['inaccurateManifestTolerance'] == undefined) {
         config['streaming']['inaccurateManifestTolerance'] = 0;
@@ -3214,6 +3215,9 @@ shaka.Player = class extends shaka.util.FakeEventTarget {
       if (config['streaming']['rebufferingGoal'] == undefined) {
         config['streaming']['rebufferingGoal'] = 0.01;
       }
+      if (config['streaming']['segmentPrefetchLimit'] == undefined) {
+        config['streaming']['segmentPrefetchLimit'] = 2;
+      }
     }
     const ret = shaka.util.PlayerConfiguration.mergeConfigObjects(
         this.config_, config, this.defaultConfig_());
diff --git a/lib/util/player_configuration.js b/lib/util/player_configuration.js
index af23f1d24b..71b1105cc3 100644
--- a/lib/util/player_configuration.js
+++ b/lib/util/player_configuration.js
@@ -206,6 +206,8 @@ shaka.util.PlayerConfiguration = class {
       observeQualityChanges: false,
       maxDisabledTime: 30,
       parsePrftBox: false,
+      // When low latency streaming is enabled, segmentPrefetchLimit will
+      // default to 2 if not specified.
       segmentPrefetchLimit: 0,
     };
 
diff --git a/test/player_unit.js b/test/player_unit.js
index c7f7dea61b..54c892aff9 100644
--- a/test/player_unit.js
+++ b/test/player_unit.js
@@ -1291,19 +1291,23 @@ describe('Player', () => {
           lowLatencyMode: true,
           rebufferingGoal: 1,
           inaccurateManifestTolerance: 1,
+          segmentPrefetchLimit: 1,
         },
       });
       expect(player.getConfiguration().streaming.rebufferingGoal).toBe(1);
       expect(player.getConfiguration().streaming.inaccurateManifestTolerance)
           .toBe(1);
+      expect(player.getConfiguration().streaming.segmentPrefetchLimit).toBe(1);
 
       // When low latency streaming gets enabled, rebufferingGoal will default
-      // to 0.01 if unless specified, and inaccurateManifestTolerance will
-      // default to 0 unless specified.
+      // to 0.01 if unless specified, inaccurateManifestTolerance will
+      // default to 0 unless specified, and segmentPrefetchLimit will
+      // default to 2 unless specified.
       player.configure('streaming.lowLatencyMode', true);
       expect(player.getConfiguration().streaming.rebufferingGoal).toBe(0.01);
       expect(player.getConfiguration().streaming.inaccurateManifestTolerance)
           .toBe(0);
+      expect(player.getConfiguration().streaming.segmentPrefetchLimit).toBe(2);
     });
   });