--- a/dom/media/MediaCache.cpp
+++ b/dom/media/MediaCache.cpp
@@ -2013,16 +2013,19 @@ MediaCacheStream::NotifyDataReceived(uin
 
   if (mLoadID != aLoadID) {
     // mChannelOffset is updated to a new position when loading a new channel.
     // We should discard the data coming from the old channel so it won't be
     // stored to the wrong positoin.
     return;
   }
 
+  // True if we commit any blocks to the cache.
+  bool cacheUpdated = false;
+
   auto source = MakeSpan<const uint8_t>(aData, aCount);
 
   // We process the data one block (or part of a block) at a time
   while (!source.IsEmpty()) {
     // The data we've collected so far in the partial block.
     auto partial = MakeSpan<const uint8_t>(mPartialBlockBuffer.get(),
                                            OffsetInBlock(mChannelOffset));
 
@@ -2040,16 +2043,17 @@ MediaCacheStream::NotifyDataReceived(uin
       mMediaCache->AllocateAndWriteBlock(
         this,
         OffsetToBlockIndexUnchecked(mChannelOffset),
         mMetadataInPartialBlockBuffer ? MODE_METADATA : MODE_PLAYBACK,
         partial,
         source.First(remaining));
       source = source.From(remaining);
       mChannelOffset += remaining;
+      cacheUpdated = true;
     } else {
       // The buffer to be filled in the partial block.
       auto buf = MakeSpan<uint8_t>(mPartialBlockBuffer.get() + partial.Length(),
                                    remaining);
       memcpy(buf.Elements(), source.Elements(), source.Length());
       mChannelOffset += source.Length();
       break;
     }
@@ -2059,20 +2063,22 @@ MediaCacheStream::NotifyDataReceived(uin
   while (MediaCacheStream* stream = iter.Next()) {
     if (stream->mStreamLength >= 0) {
       // The stream is at least as long as what we've read
       stream->mStreamLength = std::max(stream->mStreamLength, mChannelOffset);
     }
     stream->mClient->CacheClientNotifyDataReceived();
   }
 
-  // Notify in case there's a waiting reader
   // XXX it would be fairly easy to optimize things a lot more to
   // avoid waking up reader threads unnecessarily
-  mon.NotifyAll();
+  if (cacheUpdated) {
+    // Wake up the reader who is waiting for the committed blocks.
+    mon.NotifyAll();
+  }
 }
 
 void
 MediaCacheStream::FlushPartialBlockInternal(bool aNotifyAll,
                                             ReentrantMonitorAutoEnter& aReentrantMonitor)
 {
   NS_ASSERTION(NS_IsMainThread(), "Only call on main thread");