From 68f7a0eb2a8574645592e069c63813e0c97c5e66 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?=C3=81lvaro=20Velad=20Galv=C3=A1n?= <ladvan91@hotmail.com>
Date: Thu, 29 Jun 2023 21:59:45 +0200
Subject: [PATCH] feat: Optimize appendBuffer operations for init segments
 (#5377)

---
 lib/media/media_source_engine.js | 59 ++++++++++++++++++--------------
 1 file changed, 33 insertions(+), 26 deletions(-)

diff --git a/lib/media/media_source_engine.js b/lib/media/media_source_engine.js
index 94e915b377..b83795d6d9 100644
--- a/lib/media/media_source_engine.js
+++ b/lib/media/media_source_engine.js
@@ -133,6 +133,9 @@ shaka.media.MediaSourceEngine = class {
     /** @private {boolean} */
     this.ignoreManifestTimestampsInSegmentsMode_ = false;
 
+    /** @private {boolean} */
+    this.attemptTimestampOffsetCalculation_ = false;
+
     /** @private {!shaka.util.PublicPromise.<number>} */
     this.textSequenceModeOffset_ = new shaka.util.PublicPromise();
   }
@@ -383,6 +386,10 @@ shaka.media.MediaSourceEngine = class {
     this.ignoreManifestTimestampsInSegmentsMode_ =
       ignoreManifestTimestampsInSegmentsMode;
 
+    this.attemptTimestampOffsetCalculation_ = !this.sequenceMode_ &&
+        this.manifestType_ == shaka.media.ManifestParser.HLS &&
+        !this.ignoreManifestTimestampsInSegmentsMode_;
+
     for (const contentType of streamsByType.keys()) {
       const stream = streamsByType.get(contentType);
       this.initSourceBuffer_(contentType, stream);
@@ -751,39 +758,39 @@ shaka.media.MediaSourceEngine = class {
       return;
     }
 
-    const attemptTimestampOffsetCalculation = !this.sequenceMode_ &&
-        this.manifestType_ == shaka.media.ManifestParser.HLS &&
-        !this.ignoreManifestTimestampsInSegmentsMode_;
-
     let timestampOffset = this.sourceBuffers_[contentType].timestampOffset;
 
     let mimeType = this.sourceBufferTypes_[contentType];
     if (this.transmuxers_[contentType]) {
       mimeType = this.transmuxers_[contentType].getOrginalMimeType();
     }
-    const timestamp = this.getTimestampAndDispatchMetadata_(
-        contentType, data, reference, mimeType, timestampOffset);
-    if (timestamp != null && reference) {
-      const calculatedTimestampOffset = reference.startTime - timestamp;
-      const timestampOffsetDifference =
-          Math.abs(timestampOffset - calculatedTimestampOffset);
-      if (timestampOffsetDifference >= 0.1 || seeked || adaptation) {
-        timestampOffset = calculatedTimestampOffset;
-        if (attemptTimestampOffsetCalculation) {
-          this.enqueueOperation_(contentType, () => this.abort_(contentType));
-          this.enqueueOperation_(
-              contentType,
-              () => this.setTimestampOffset_(contentType, timestampOffset));
+    if (reference) {
+      const timestamp = this.getTimestampAndDispatchMetadata_(
+          contentType, data, reference, mimeType, timestampOffset);
+      if (timestamp != null) {
+        const calculatedTimestampOffset = reference.startTime - timestamp;
+        const timestampOffsetDifference =
+            Math.abs(timestampOffset - calculatedTimestampOffset);
+        if (timestampOffsetDifference >= 0.1 || seeked || adaptation) {
+          timestampOffset = calculatedTimestampOffset;
+          if (this.attemptTimestampOffsetCalculation_) {
+            this.enqueueOperation_(
+                contentType,
+                () => this.abort_(contentType));
+            this.enqueueOperation_(
+                contentType,
+                () => this.setTimestampOffset_(contentType, timestampOffset));
+          }
+        }
+        // Timestamps can only be reliably extracted from video, not audio.
+        // Packed audio formats do not have internal timestamps at all.
+        // Prefer video for this when available.
+        const isBestSourceBufferForTimestamps =
+            contentType == ContentType.VIDEO ||
+            !(ContentType.VIDEO in this.sourceBuffers_);
+        if (this.sequenceMode_ && isBestSourceBufferForTimestamps) {
+          this.textSequenceModeOffset_.resolve(timestampOffset);
         }
-      }
-      // Timestamps can only be reliably extracted from video, not audio.
-      // Packed audio formats do not have internal timestamps at all.
-      // Prefer video for this when available.
-      const isBestSourceBufferForTimestamps =
-          contentType == ContentType.VIDEO ||
-          !(ContentType.VIDEO in this.sourceBuffers_);
-      if (this.sequenceMode_ && isBestSourceBufferForTimestamps) {
-        this.textSequenceModeOffset_.resolve(timestampOffset);
       }
     }
     if (hasClosedCaptions && contentType == ContentType.VIDEO) {