--- a/dom/media/MediaMIMETypes.cpp
+++ b/dom/media/MediaMIMETypes.cpp
@@ -5,16 +5,44 @@
  * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
 
 #include "MediaMIMETypes.h"
 
 #include "nsContentTypeParser.h"
 
 namespace mozilla {
 
+template <int N>
+static bool
+StartsWith(const nsACString& string, const char (&prefix)[N])
+{
+    if (N - 1 > string.Length()) {
+      return false;
+    }
+    return memcmp(string.Data(), prefix, N - 1) == 0;
+}
+
+bool
+MediaMIMEType::HasApplicationMajorType() const
+{
+  return StartsWith(mMIMEType, "application/");
+}
+
+bool
+MediaMIMEType::HasAudioMajorType() const
+{
+  return StartsWith(mMIMEType, "audio/");
+}
+
+bool
+MediaMIMEType::HasVideoMajorType() const
+{
+  return StartsWith(mMIMEType, "video/");
+}
+
 MediaMIMEType::MediaMIMEType(const nsACString& aType)
   : mMIMEType(aType)
 {
 }
 
 Maybe<MediaMIMEType>
 MakeMediaMIMEType(const nsAString& aType)
 {

--- a/dom/media/MediaMIMETypes.h
+++ b/dom/media/MediaMIMETypes.h
@@ -71,16 +71,26 @@ public:
   {
     return mMIMEType.Equals(aOther.mMIMEType);
   }
   bool operator!=(const MediaMIMEType& aOther) const
   {
     return !mMIMEType.Equals(aOther.mMIMEType);
   }
 
+  // True if type starts with "application/".
+  bool HasApplicationMajorType() const;
+  // True if type starts with "audio/".
+  // Note that some audio content could be stored in a "video/..." container!
+  bool HasAudioMajorType() const;
+  // True if type starts with "video/".
+  // Note that this does not guarantee 100% that the content is actually video!
+  // (e.g., "video/webm" could contain a vorbis audio track.)
+  bool HasVideoMajorType() const;
+
 private:
   friend Maybe<MediaMIMEType> MakeMediaMIMEType(const nsAString& aType);
   friend class MediaExtendedMIMEType;
   explicit MediaMIMEType(const nsACString& aType);
 
   nsCString mMIMEType; // UTF8 MIME "type/subtype".
 };