From c1a94baae7505c362be26062923a8fa938e47095 Mon Sep 17 00:00:00 2001
From: baconz <baconz@users.noreply.github.com>
Date: Sun, 2 Jul 2023 23:07:29 -0700
Subject: [PATCH] fix: gap jumping when gap exists at start position (#5384)

Before playback starts the video element reports as seeking == true, but
because we haven't installed our seek listener yet, the gap controller
does not receive the seek event.

To work around this, we explicitly tell the gap controller when playback
starts so that it knows the startup position, and can synthesize a seek
event.
---
 lib/media/gap_jumping_controller.js | 19 +++++++++++++++++--
 lib/media/playhead.js               | 11 +++++++++++
 lib/media/video_wrapper.js          |  7 ++++++-
 3 files changed, 34 insertions(+), 3 deletions(-)

diff --git a/lib/media/gap_jumping_controller.js b/lib/media/gap_jumping_controller.js
index cea9059c58..27d93ab6c1 100644
--- a/lib/media/gap_jumping_controller.js
+++ b/lib/media/gap_jumping_controller.js
@@ -58,6 +58,9 @@ shaka.media.GapJumpingController = class {
     /** @private {number} */
     this.prevReadyState_ = video.readyState;
 
+    /** @private {number} */
+    this.startTime_ = 0;
+
     /** @private {number} */
     this.gapsJumped_ = 0;
 
@@ -123,6 +126,18 @@ shaka.media.GapJumpingController = class {
     this.onPollGapJump_();
   }
 
+  /**
+   * Called when playback has started and the video element is
+   * listening for seeks.
+   *
+   * @param {number} startTime
+   */
+  onStarted(startTime) {
+    if (this.video_.seeking && !this.seekingEventReceived_) {
+      this.seekingEventReceived_ = true;
+      this.startTime_ = startTime;
+    }
+  }
 
   /** Called when a seek has started. */
   onSeeking() {
@@ -164,8 +179,8 @@ shaka.media.GapJumpingController = class {
     // while paused on a livestream.  We make an exception for time 0, since we
     // may be _required_ to seek on startup before play can begin, but only if
     // autoplay is enabled.
-    if (this.video_.paused && (this.video_.currentTime != 0 ||
-      (!this.video_.autoplay && this.video_.currentTime == 0))) {
+    if (this.video_.paused && (this.video_.currentTime != this.startTime_ ||
+      (!this.video_.autoplay && this.video_.currentTime == this.startTime_))) {
       return;
     }
 
diff --git a/lib/media/playhead.js b/lib/media/playhead.js
index 9cad395943..27a3a2e4aa 100644
--- a/lib/media/playhead.js
+++ b/lib/media/playhead.js
@@ -251,6 +251,7 @@ shaka.media.MediaSourcePlayhead = class {
     this.videoWrapper_ = new shaka.media.VideoWrapper(
         mediaElement,
         () => this.onSeeking_(),
+        (realStartTime) => this.onStarted_(realStartTime),
         this.getStartTime_(startTime));
 
     /** @type {shaka.util.Timer} */
@@ -390,6 +391,16 @@ shaka.media.MediaSourcePlayhead = class {
     }
   }
 
+  /**
+   * Called when the video element has started up and is listening for new seeks
+   *
+   * @param {number} startTime
+   * @private
+   */
+  onStarted_(startTime) {
+    this.gapController_.onStarted(startTime);
+  }
+
   /**
    * Handles when a seek happens on the video.
    *
diff --git a/lib/media/video_wrapper.js b/lib/media/video_wrapper.js
index 6ddc5e0346..a76539e804 100644
--- a/lib/media/video_wrapper.js
+++ b/lib/media/video_wrapper.js
@@ -27,15 +27,19 @@ shaka.media.VideoWrapper = class {
   /**
    * @param {!HTMLMediaElement} video
    * @param {function()} onSeek Called when the video seeks.
+   * @param {function(number)} onStarted Called when the video has started.
    * @param {number} startTime The time to start at.
    */
-  constructor(video, onSeek, startTime) {
+  constructor(video, onSeek, onStarted, startTime) {
     /** @private {HTMLMediaElement} */
     this.video_ = video;
 
     /** @private {function()} */
     this.onSeek_ = onSeek;
 
+    /** @private {function(number)} */
+    this.onStarted_ = onStarted;
+
     /** @private {number} */
     this.startTime_ = startTime;
 
@@ -165,6 +169,7 @@ shaka.media.VideoWrapper = class {
     this.started_ = true;
 
     this.eventManager_.listen(this.video_, 'seeking', () => this.onSeek_());
+    this.onStarted_(this.video_.currentTime);
   }
 };