diff --git a/dom/media/fmp4/MP4Decoder.cpp b/dom/media/fmp4/MP4Decoder.cpp
index 7133ec197c7d..30dc6cc2c2f7 100644
--- a/dom/media/fmp4/MP4Decoder.cpp
+++ b/dom/media/fmp4/MP4Decoder.cpp
@@ -168,6 +168,13 @@ MP4Decoder::IsH264(const nsACString& aMimeType)
          aMimeType.EqualsLiteral("video/avc");
 }
 
+/* static */
+bool
+MP4Decoder::IsAAC(const nsACString& aMimeType)
+{
+  return aMimeType.EqualsLiteral("audio/mp4a-latm");
+}
+
 /* static */
 bool
 MP4Decoder::IsEnabled()
diff --git a/dom/media/fmp4/MP4Decoder.h b/dom/media/fmp4/MP4Decoder.h
index 0bf8b9959bbc..ad5fba7b5440 100644
--- a/dom/media/fmp4/MP4Decoder.h
+++ b/dom/media/fmp4/MP4Decoder.h
@@ -40,6 +40,11 @@ public:
   // space matters.
   static bool IsH264(const nsACString& aMimeType);
 
+  // Return true if aMimeType is a one of the strings used by our demuxers to
+  // identify AAC. Does not parse general content type strings, i.e. white
+  // space matters.
+  static bool IsAAC(const nsACString& aMimeType);
+
   // Returns true if the MP4 backend is preffed on.
   static bool IsEnabled();