From b9bb199bea931e9ebdd59f42bfe7eb962c1f6226 Mon Sep 17 00:00:00 2001
From: Seth Madison <seth@philo.com>
Date: Fri, 23 Jun 2023 13:44:26 -0700
Subject: [PATCH] feat: Optimizations to improve performance of the period
 combiner.

For manifests with many streams, we saw the bullk of the manifest parse
time going towards period combiner. Specifically: splitting codecs and
comparing DRMs. This change cuts our manifest parse time for large manifests
by nearly 30%.

There are two changes:

1. Memoize the normalized codecs inside the period combiner.
2. Short circuit the DRM compatibility check if the DRMInfos arrays
   are the same object. We run a custom manifest parser and are therefore
   able to re-use the same drm infos array for functionally equivalent drms, but
   short circuiting also helps since in the case that the upstream period combiner
   is comparing a candidate stream with itself.
---
 lib/media/drm_engine.js |  4 ++++
 lib/util/periods.js     | 14 ++++++++++++--
 2 files changed, 16 insertions(+), 2 deletions(-)

diff --git a/lib/media/drm_engine.js b/lib/media/drm_engine.js
index b8bf2687ee..462fd4e523 100644
--- a/lib/media/drm_engine.js
+++ b/lib/media/drm_engine.js
@@ -2005,6 +2005,10 @@ shaka.media.DrmEngine = class {
       return true;
     }
 
+    if (drms1 === drms2) {
+      return true;
+    }
+
     return shaka.media.DrmEngine.getCommonDrmInfos(
         drms1, drms2).length > 0;
   }
diff --git a/lib/util/periods.js b/lib/util/periods.js
index dd54ad0df1..3a3e6939a0 100644
--- a/lib/util/periods.js
+++ b/lib/util/periods.js
@@ -1067,8 +1067,13 @@ shaka.util.PeriodCombiner = class {
    * @private
    */
   static areAVStreamsCompatible_(outputStream, candidate) {
-    const getCodec = (codecs) =>
-      shaka.util.MimeUtils.getNormalizedCodec(codecs);
+    const getCodec = (codecs) => {
+      if (!shaka.util.PeriodCombiner.memoizedCodecs.has(codecs)) {
+        const normalizedCodec = shaka.util.MimeUtils.getNormalizedCodec(codecs);
+        shaka.util.PeriodCombiner.memoizedCodecs.set(codecs, normalizedCodec);
+      }
+      return shaka.util.PeriodCombiner.memoizedCodecs.get(codecs);
+    };
     // Check MIME type and codecs, which should always be the same.
     if (candidate.mimeType != outputStream.mimeType ||
         getCodec(candidate.codecs) != getCodec(outputStream.codecs)) {
@@ -1666,3 +1671,8 @@ shaka.util.PeriodCombiner.BetterOrWorse = {
   EQUAL: 0,
   WORSE: -1,
 };
+
+/**
+ * @private {Map<string, string>}
+ */
+shaka.util.PeriodCombiner.memoizedCodecs = new Map();