--- a/dom/media/platforms/ffmpeg/FFmpegRDFTTypes.h
+++ b/dom/media/platforms/ffmpeg/FFmpegRDFTTypes.h
@@ -21,9 +21,16 @@ enum RDFTransformType {
 extern "C" {
 
   typedef RDFTContext* (*AvRdftInitFn)(int nbits, enum RDFTransformType trans);
   typedef void (*AvRdftCalcFn)(RDFTContext *s, FFTSample *data);
   typedef void (*AvRdftEndFn)(RDFTContext *s);
 
 }
 
+struct FFmpegRDFTFuncs
+{
+    AvRdftInitFn init;
+    AvRdftCalcFn calc;
+    AvRdftEndFn end;
+};
+
 #endif // FFmpegRDFTTypes_h

--- a/dom/media/platforms/ffmpeg/ffvpx/FFVPXRuntimeLinker.cpp
+++ b/dom/media/platforms/ffmpeg/ffvpx/FFVPXRuntimeLinker.cpp
@@ -57,16 +57,17 @@ MozAVLink(nsIFile* aFile)
 
 /* static */ bool
 FFVPXRuntimeLinker::Init()
 {
   if (sLinkStatus) {
     return sLinkStatus == LinkStatus_SUCCEEDED;
   }
 
+  MOZ_ASSERT(NS_IsMainThread());
   sLinkStatus = LinkStatus_FAILED;
 
   // We retrieve the path of the lgpllibs library as this is where mozavcodec
   // and mozavutil libs are located.
   PathString lgpllibsname = GetLibraryName(nullptr, "lgpllibs");
   if (lgpllibsname.IsEmpty()) {
     return false;
   }
@@ -115,9 +116,25 @@ FFVPXRuntimeLinker::Init()
 FFVPXRuntimeLinker::CreateDecoderModule()
 {
   if (!Init()) {
     return nullptr;
   }
   return FFmpegDecoderModule<FFVPX_VERSION>::Create(&sFFVPXLib);
 }
 
+/* static */ void
+FFVPXRuntimeLinker::GetRDFTFuncs(FFmpegRDFTFuncs* aOutFuncs)
+{
+  MOZ_ASSERT(sLinkStatus != LinkStatus_INIT);
+  if (sFFVPXLib.av_rdft_init &&
+      sFFVPXLib.av_rdft_calc &&
+      sFFVPXLib.av_rdft_end) {
+    aOutFuncs->init = sFFVPXLib.av_rdft_init;
+    aOutFuncs->calc = sFFVPXLib.av_rdft_calc;
+    aOutFuncs->end = sFFVPXLib.av_rdft_end;
+  } else {
+    NS_WARNING("RDFT functions expected but not found");
+    *aOutFuncs = FFmpegRDFTFuncs(); // zero
+  }
+}
+
 } // namespace mozilla

--- a/dom/media/platforms/ffmpeg/ffvpx/FFVPXRuntimeLinker.h
+++ b/dom/media/platforms/ffmpeg/ffvpx/FFVPXRuntimeLinker.h
@@ -4,26 +4,34 @@
  * 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 __FFVPXRuntimeLinker_h__
 #define __FFVPXRuntimeLinker_h__
 
 #include "PlatformDecoderModule.h"
 
+struct FFmpegRDFTFuncs;
+
 namespace mozilla
 {
 
 class FFVPXRuntimeLinker
 {
 public:
+  // Main thread only.
   static bool Init();
+  // Main thread or after Init().
   static already_AddRefed<PlatformDecoderModule> CreateDecoderModule();
 
+  // Call (on any thread) after Init().
+  static void GetRDFTFuncs(FFmpegRDFTFuncs* aOutFuncs);
+
 private:
+  // Set once on the main thread and then read from other threads.
   static enum LinkStatus {
     LinkStatus_INIT = 0,
     LinkStatus_FAILED,
     LinkStatus_SUCCEEDED
   } sLinkStatus;
 };
 
 }

--- a/dom/media/platforms/moz.build
+++ b/dom/media/platforms/moz.build
@@ -43,16 +43,19 @@ DIRS += [
     'omx'
 ]
 
 if CONFIG['MOZ_WMF']:
     DIRS += [ 'wmf' ];
 
 if CONFIG['MOZ_FFVPX'] or CONFIG['MOZ_FFMPEG']:
     # common code to either FFmpeg or FFVPX
+    EXPORTS += [
+        'ffmpeg/FFmpegRDFTTypes.h',
+    ]
     UNIFIED_SOURCES += [
         'ffmpeg/FFmpegLibWrapper.cpp',
     ]
 
 if CONFIG['MOZ_FFVPX']:
     DIRS += [
         'ffmpeg/ffvpx',
     ]