1 files changed, 7 insertions, 2 deletions
diff --git a/dom/media/fmp4/MP4Demuxer.cpp b/dom/media/fmp4/MP4Demuxer.cpp
index 70b176699..646897468 100644
--- a/dom/media/fmp4/MP4Demuxer.cpp
+++ b/dom/media/fmp4/MP4Demuxer.cpp
@@ -349,8 +349,13 @@ MP4TrackDemuxer::GetNextSample()
   if (sample->mCrypto.mValid) {
     nsAutoPtr<MediaRawDataWriter> writer(sample->CreateWriter());
     writer->mCrypto.mMode = mInfo->mCrypto.mMode;
-    writer->mCrypto.mIVSize = mInfo->mCrypto.mIVSize;
-    writer->mCrypto.mKeyId.AppendElements(mInfo->mCrypto.mKeyId);
+
+    // Only use the default key parsed from the moov if we haven't already got
+    // one from the sample group description.
+    if (writer->mCrypto.mKeyId.Length() == 0) {
+      writer->mCrypto.mIVSize = mInfo->mCrypto.mIVSize;
+      writer->mCrypto.mKeyId.AppendElements(mInfo->mCrypto.mKeyId);
+    }
   }
   return sample.forget();
 }