diff --git a/dom/media/mediasource/MediaSource.cpp b/dom/media/mediasource/MediaSource.cpp
index 0b3d77be62..a5b2065599 100644
--- a/dom/media/mediasource/MediaSource.cpp
+++ b/dom/media/mediasource/MediaSource.cpp
@@ -338,6 +338,58 @@ MediaSource::Enabled(JSContext* cx, JSObject* aGlobal)
 return Preferences::GetBool("media.mediasource.enabled");
 }
 
+void
+MediaSource::SetLiveSeekableRange(double aStart, double aEnd, ErrorResult& aRv)
+{
+  MOZ_ASSERT(NS_IsMainThread());
+
+  // 1. If the readyState attribute is not "open" then throw an InvalidStateError
+  // exception and abort these steps.
+  // 2. If the updating attribute equals true on any SourceBuffer in
+  // sourceBuffers, then throw an InvalidStateError exception and abort these
+  // steps.
+  if (mReadyState != MediaSourceReadyState::Open ||
+      mSourceBuffers->AnyUpdating()) {
+    aRv.Throw(NS_ERROR_DOM_INVALID_STATE_ERR);
+    return;
+  }
+
+  // 3. If start is negative or greater than end, then throw a TypeError
+  // exception and abort these steps.
+  if (aStart < 0 || aStart > aEnd) {
+    aRv.Throw(NS_ERROR_DOM_TYPE_ERR);
+    return;
+  }
+
+  // 4. Set live seekable range to be a new normalized TimeRanges object
+  // containing a single range whose start position is start and end position is
+  // end.
+  mLiveSeekableRange =
+    Some(media::TimeInterval(media::TimeUnit::FromSeconds(aStart),
+                             media::TimeUnit::FromSeconds(aEnd)));
+}
+
+void
+MediaSource::ClearLiveSeekableRange(ErrorResult& aRv)
+{
+  MOZ_ASSERT(NS_IsMainThread());
+
+  // 1. If the readyState attribute is not "open" then throw an InvalidStateError
+  // exception and abort these steps.
+  // 2. If the updating attribute equals true on any SourceBuffer in
+  // sourceBuffers, then throw an InvalidStateError exception and abort these
+  // steps.
+  if (mReadyState != MediaSourceReadyState::Open ||
+      mSourceBuffers->AnyUpdating()) {
+    aRv.Throw(NS_ERROR_DOM_INVALID_STATE_ERR);
+    return;
+  }
+
+  // 3. If live seekable range contains a range, then set live seekable range to
+  // be a new empty TimeRanges object.
+  mLiveSeekableRange.reset();
+}
+
 bool
 MediaSource::Attach(MediaSourceDecoder* aDecoder)
 {
diff --git a/dom/media/mediasource/MediaSource.h b/dom/media/mediasource/MediaSource.h
index 60106fb0cf..6f6790813b 100644
--- a/dom/media/mediasource/MediaSource.h
+++ b/dom/media/mediasource/MediaSource.h
@@ -19,6 +19,7 @@
 #include "nsID.h"
 #include "nsISupports.h"
 #include "nscore.h"
+#include "TimeUnits.h"
 
 struct JSContext;
 class JSObject;
@@ -64,6 +65,10 @@ public:
   void RemoveSourceBuffer(SourceBuffer& aSourceBuffer, ErrorResult& aRv);
 
   void EndOfStream(const Optional<MediaSourceEndOfStreamError>& aError, ErrorResult& aRv);
+
+  void SetLiveSeekableRange(double aStart, double aEnd, ErrorResult& aRv);
+  void ClearLiveSeekableRange(ErrorResult& aRv);
+
   static bool IsTypeSupported(const GlobalObject&, const nsAString& aType);
 
   static bool Enabled(JSContext* cx, JSObject* aGlobal);
@@ -118,6 +123,12 @@ public:
   // buffered data. Used for debugging purposes.
   void GetMozDebugReaderData(nsAString& aString);
 
+  bool HasLiveSeekableRange() const { return mLiveSeekableRange.isSome(); }
+  media::TimeInterval LiveSeekableRange() const
+  {
+    return mLiveSeekableRange.value();
+  }
+
 private:
   // MediaSourceDecoder uses DurationChange to set the duration
   // without hitting the checks in SetDuration.
@@ -154,6 +165,8 @@ private:
   nsRefPtr<nsIPrincipal> mPrincipal;
 
   MediaSourceReadyState mReadyState;
+  
+  Maybe<media::TimeInterval> mLiveSeekableRange;
 
   bool mFirstSourceBufferInitialized;
 };
diff --git a/dom/media/mediasource/MediaSourceDecoder.cpp b/dom/media/mediasource/MediaSourceDecoder.cpp
index 711816e278..30d3ab0b25 100644
--- a/dom/media/mediasource/MediaSourceDecoder.cpp
+++ b/dom/media/mediasource/MediaSourceDecoder.cpp
@@ -91,6 +91,21 @@ MediaSourceDecoder::GetSeekable()
     // Return empty range.
   } else if (duration > 0 && mozilla::IsInfinite(duration)) {
     media::TimeIntervals buffered = mReader->GetBuffered();
+
+    // 1. If live seekable range is not empty:
+    if (mMediaSource->HasLiveSeekableRange()) {
+      // 1. Let union ranges be the union of live seekable range and the
+      // HTMLMediaElement.buffered attribute.
+      media::TimeIntervals unionRanges =
+        buffered + mMediaSource->LiveSeekableRange();
+      // 2. Return a single range with a start time equal to the earliest start
+      // time in union ranges and an end time equal to the highest end time in
+      // union ranges and abort these steps.
+      seekable +=
+        media::TimeInterval(unionRanges.GetStart(), unionRanges.GetEnd());
+      return seekable;
+    }
+
     if (buffered.Length()) {
       seekable +=
         media::TimeInterval(media::TimeUnit::FromSeconds(0), buffered.GetEnd());
diff --git a/dom/webidl/MediaSource.webidl b/dom/webidl/MediaSource.webidl
index 562f8ebb8b..95a7026fe9 100644
--- a/dom/webidl/MediaSource.webidl
+++ b/dom/webidl/MediaSource.webidl
@@ -34,6 +34,10 @@ interface MediaSource : EventTarget {
   void removeSourceBuffer(SourceBuffer sourceBuffer);
   [Throws]
   void endOfStream(optional MediaSourceEndOfStreamError error);
+  [Throws]
+  void setLiveSeekableRange(double start, double end);
+  [Throws]
+  void clearLiveSeekableRange();
   static boolean isTypeSupported(DOMString type);
   [ChromeOnly]
   readonly attribute DOMString mozDebugReaderData;