--- a/dom/media/VideoUtils.cpp
+++ b/dom/media/VideoUtils.cpp
@@ -4,16 +4,17 @@
 
 #include "VideoUtils.h"
 
 #include "mozilla/Base64.h"
 #include "mozilla/TaskQueue.h"
 #include "mozilla/Telemetry.h"
 #include "mozilla/Function.h"
 
+#include "MediaContentType.h"
 #include "MediaPrefs.h"
 #include "MediaResource.h"
 #include "TimeUnits.h"
 #include "nsMathUtils.h"
 #include "nsSize.h"
 #include "VorbisUtils.h"
 #include "ImageContainer.h"
 #include "mozilla/SharedThreadPool.h"
@@ -471,9 +472,55 @@ IsVP8CodecString(const nsAString& aCodec
 
 bool
 IsVP9CodecString(const nsAString& aCodec)
 {
   return aCodec.EqualsLiteral("vp9") ||
          aCodec.EqualsLiteral("vp9.0");
 }
 
+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;
+}
+
+UniquePtr<TrackInfo>
+CreateTrackInfoWithMIMEType(const nsACString& aCodecMIMEType)
+{
+  UniquePtr<TrackInfo> trackInfo;
+  if (StartsWith(aCodecMIMEType, "audio/")) {
+    trackInfo.reset(new AudioInfo());
+    trackInfo->mMimeType = aCodecMIMEType;
+  } else if (StartsWith(aCodecMIMEType, "video/")) {
+    trackInfo.reset(new VideoInfo());
+    trackInfo->mMimeType = aCodecMIMEType;
+  }
+  return trackInfo;
+}
+
+UniquePtr<TrackInfo>
+CreateTrackInfoWithMIMETypeAndContentTypeExtraParameters(
+  const nsACString& aCodecMIMEType,
+  const MediaContentType& aContentType)
+{
+  UniquePtr<TrackInfo> trackInfo = CreateTrackInfoWithMIMEType(aCodecMIMEType);
+  if (trackInfo) {
+    VideoInfo* videoInfo = trackInfo->GetAsVideoInfo();
+    if (videoInfo) {
+      Maybe<int32_t> maybeWidth = aContentType.GetWidth();
+      if (maybeWidth && *maybeWidth > 0) {
+        videoInfo->mImage.width = *maybeWidth;
+      }
+      Maybe<int32_t> maybeHeight = aContentType.GetHeight();
+      if (maybeHeight && *maybeHeight > 0) {
+        videoInfo->mImage.height = *maybeHeight;
+      }
+    }
+  }
+  return trackInfo;
+}
+
 } // end namespace mozilla

--- a/dom/media/VideoUtils.h
+++ b/dom/media/VideoUtils.h
@@ -2,21 +2,23 @@
 /* vim:set ts=2 sw=2 sts=2 et cindent: */
 /* This Source Code Form is subject to the terms of the Mozilla Public
  * License, v. 2.0. If a copy of the MPL was not distributed with this
  * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
 
 #ifndef VideoUtils_h
 #define VideoUtils_h
 
+#include "MediaInfo.h"
 #include "mozilla/Attributes.h"
 #include "mozilla/CheckedInt.h"
 #include "mozilla/MozPromise.h"
 #include "mozilla/ReentrantMonitor.h"
 #include "mozilla/RefPtr.h"
+#include "mozilla/UniquePtr.h"
 
 #include "nsAutoPtr.h"
 #include "nsIThread.h"
 #include "nsSize.h"
 #include "nsRect.h"
 
 #include "nsThreadUtils.h"
 #include "prtime.h"
@@ -34,16 +36,18 @@ using mozilla::CheckedUint32;
 // dependent on other changes which we don't want to wait for. We plan to
 // remove this file in the near future.
 
 
 // This belongs in xpcom/monitor/Monitor.h, once we've made
 // mozilla::Monitor non-reentrant.
 namespace mozilla {
 
+class MediaContentType;
+
 // EME Key System String.
 extern const nsLiteralCString kEMEKeySystemClearkey;
 extern const nsLiteralCString kEMEKeySystemWidevine;
 extern const nsLiteralCString kEMEKeySystemPrimetime;
 
 /**
  * ReentrantMonitorConditionallyEnter
  *
@@ -342,16 +346,27 @@ bool
 IsAACCodecString(const nsAString& aCodec);
 
 bool
 IsVP8CodecString(const nsAString& aCodec);
 
 bool
 IsVP9CodecString(const nsAString& aCodec);
 
+// Try and create a TrackInfo with a given codec MIME type.
+UniquePtr<TrackInfo>
+CreateTrackInfoWithMIMEType(const nsACString& aCodecMIMEType);
+
+// Try and create a TrackInfo with a given codec MIME type, and optional extra
+// parameters from a content type (its MIME type and codecs are ignored).
+UniquePtr<TrackInfo>
+CreateTrackInfoWithMIMETypeAndContentTypeExtraParameters(
+  const nsACString& aCodecMIMEType,
+  const MediaContentType& aContentType);
+
 template <typename String>
 class StringListRange
 {
   typedef typename String::char_type CharType;
   typedef const CharType* Pointer;
 
 public:
   // Iterator into range, trims items and skips empty items.