diff --git a/content/media/mediasource/SourceBuffer.cpp b/content/media/mediasource/SourceBuffer.cpp
index c854dd855c04..c474f46234bb 100644
--- a/content/media/mediasource/SourceBuffer.cpp
+++ b/content/media/mediasource/SourceBuffer.cpp
@@ -490,6 +490,15 @@ SourceBuffer::Evict(double aStart, double aEnd)
   }
 }
 
+bool
+SourceBuffer::ContainsTime(double aTime)
+{
+  double start = 0.0;
+  double end = 0.0;
+  GetBufferedStartEndTime(&start, &end);
+  return aTime >= start && aTime <= end;
+}
+
 NS_IMPL_CYCLE_COLLECTION_INHERITED_1(SourceBuffer, DOMEventTargetHelper,
                                      mMediaSource)
 
diff --git a/content/media/mediasource/SourceBuffer.h b/content/media/mediasource/SourceBuffer.h
index 94262a276a24..1c10312ec1a4 100644
--- a/content/media/mediasource/SourceBuffer.h
+++ b/content/media/mediasource/SourceBuffer.h
@@ -109,6 +109,9 @@ public:
   // Evict data in the source buffer in the given time range.
   void Evict(double aStart, double aEnd);
 
+  // Returns true if the data in the source buffer contains the given time.
+  bool ContainsTime(double aTime);
+
 private:
   SourceBuffer(MediaSource* aMediaSource, const nsACString& aType);
 
diff --git a/content/media/mediasource/SourceBufferList.cpp b/content/media/mediasource/SourceBufferList.cpp
index f3c813d67057..bede8edde48d 100644
--- a/content/media/mediasource/SourceBufferList.cpp
+++ b/content/media/mediasource/SourceBufferList.cpp
@@ -111,6 +111,17 @@ SourceBufferList::Evict(double aStart, double aEnd)
   }
 }
 
+bool
+SourceBufferList::ContainsTime(double aTime)
+{
+  for (uint32_t i = 0; i < mSourceBuffers.Length(); ++i) {
+    if (!mSourceBuffers[i]->ContainsTime(aTime)) {
+      return false;
+    }
+  }
+  return true;
+}
+
 void
 SourceBufferList::Ended()
 {
diff --git a/content/media/mediasource/SourceBufferList.h b/content/media/mediasource/SourceBufferList.h
index 02ffaf80f485..d64bfaf1853d 100644
--- a/content/media/mediasource/SourceBufferList.h
+++ b/content/media/mediasource/SourceBufferList.h
@@ -77,6 +77,9 @@ public:
   // Evicts data for the given time range from each SourceBuffer in the list.
   void Evict(double aStart, double aEnd);
 
+  // Returns true if all SourceBuffers in the list contain data for the given time.
+  bool ContainsTime(double aTime);
+
 private:
   friend class AsyncEventRunner<SourceBufferList>;
   void DispatchSimpleEvent(const char* aName);