Bug 1718223 - Allow pref to control max throughput of EME decryption …

…r=bryce Adds a pref `media.eme.max-throughput-ms` to allow users to modify EME's maximum decryption rate. The default value is 200ms which is the same as the old hard-coded value. Differential Revision: https://phabricator.services.mozilla.com/D122876
dothq · Aug 18, 2021 · 228fb46 · 228fb46
1 parent 8f12a28
commit 228fb46
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Showing 3 changed files with 17 additions and 5 deletions.
diff --git a/dom/media/platforms/agnostic/eme/DecryptThroughputLimit.h b/dom/media/platforms/agnostic/eme/DecryptThroughputLimit.h
@@ -16,11 +16,13 @@ namespace mozilla {
 
 // We throttle our decrypt so that we don't decrypt more than a certain
 // duration of samples per second. This is to work around bugs in the
-// Widevine CDM. See bug 1338924 and bug 1342822.
+// Widevine CDM. See bugs 1338924, 1342822, 1718223.
 class DecryptThroughputLimit {
  public:
-  explicit DecryptThroughputLimit(nsISerialEventTarget* aTargetThread)
-      : mThrottleScheduler(aTargetThread) {}
+  explicit DecryptThroughputLimit(nsISerialEventTarget* aTargetThread,
+                                  uint32_t aMaxThroughputMs)
+      : mThrottleScheduler(aTargetThread),
+        mMaxThroughput(aMaxThroughputMs / 1000.0) {}
 
   typedef MozPromise<RefPtr<MediaRawData>, MediaResult, true> ThrottlePromise;
 
@@ -31,7 +33,8 @@ class DecryptThroughputLimit {
     MOZ_RELEASE_ASSERT(!mThrottleScheduler.IsScheduled());
 
     const TimeDuration WindowSize = TimeDuration::FromSeconds(0.1);
-    const TimeDuration MaxThroughput = TimeDuration::FromSeconds(0.2);
+    const TimeDuration MaxThroughput =
+        TimeDuration::FromSeconds(mMaxThroughput);
 
     // Forget decrypts that happened before the start of our window.
     const TimeStamp now = TimeStamp::Now();
@@ -86,6 +89,8 @@ class DecryptThroughputLimit {
   DelayedScheduler mThrottleScheduler;
   MozPromiseHolder<ThrottlePromise> mPromiseHolder;
 
+  double mMaxThroughput;
+
   struct DecryptedJob {
     TimeStamp mTimestamp;
     TimeDuration mSampleDuration;

diff --git a/dom/media/platforms/agnostic/eme/EMEDecoderModule.cpp b/dom/media/platforms/agnostic/eme/EMEDecoderModule.cpp
@@ -89,7 +89,9 @@ class EMEDecryptor : public MediaDataDecoder,
   RefPtr<InitPromise> Init() override {
     MOZ_ASSERT(!mIsShutdown);
     mThread = GetCurrentSerialEventTarget();
-    mThroughputLimiter.emplace(mThread);
+    uint32_t maxThroughputMs = StaticPrefs::media_eme_max_throughput_ms();
+    EME_LOG("EME max-throughput-ms=%" PRIu32, maxThroughputMs);
+    mThroughputLimiter.emplace(mThread, maxThroughputMs);
 
     return mDecoder->Init();
   }

diff --git a/modules/libpref/init/StaticPrefList.yaml b/modules/libpref/init/StaticPrefList.yaml
@@ -8044,6 +8044,11 @@
   value: false
   mirror: always
 
+- name: media.eme.max-throughput-ms
+  type: RelaxedAtomicUint32
+  value: 200
+  mirror: always
+
 - name: media.clearkey.persistent-license.enabled
   type: bool
   value: false