--- a/dom/media/MediaFormatReader.cpp
+++ b/dom/media/MediaFormatReader.cpp
@@ -271,30 +271,41 @@ MediaFormatReader::OnDemuxerInitDone(nsr
 {
   MOZ_ASSERT(OnTaskQueue());
   mDemuxerInitRequest.Complete();
 
   mDemuxerInitDone = true;
 
   UniquePtr<MetadataTags> tags(MakeUnique<MetadataTags>());
 
+  RefPtr<PDMFactory> platform;
+  if (!IsWaitingOnCDMResource()) {
+    platform = new PDMFactory();
+  }
+
   // To decode, we need valid video and a place to put it.
   bool videoActive = !!mDemuxer->GetNumberTracks(TrackInfo::kVideoTrack) &&
     GetImageContainer();
 
   if (videoActive) {
     // We currently only handle the first video track.
     mVideo.mTrackDemuxer = mDemuxer->GetTrackDemuxer(TrackInfo::kVideoTrack, 0);
     if (!mVideo.mTrackDemuxer) {
       mMetadataPromise.Reject(ReadMetadataFailureReason::METADATA_ERROR, __func__);
       return;
     }
+
     UniquePtr<TrackInfo> videoInfo = mVideo.mTrackDemuxer->GetInfo();
     videoActive = videoInfo && videoInfo->IsValid();
     if (videoActive) {
+      if (platform && !platform->SupportsMimeType(videoInfo->mMimeType, nullptr)) {
+        // We have no decoder for this track. Error.
+        mMetadataPromise.Reject(ReadMetadataFailureReason::METADATA_ERROR, __func__);
+        return;
+      }
       mInfo.mVideo = *videoInfo->GetAsVideoInfo();
       for (const MetadataTag& tag : videoInfo->mTags) {
         tags->Put(tag.mKey, tag.mValue);
       }
       mVideo.mCallback = new DecoderCallback(this, TrackInfo::kVideoTrack);
       mVideo.mTimeRanges = mVideo.mTrackDemuxer->GetBuffered();
       mTrackDemuxersMayBlock |= mVideo.mTrackDemuxer->GetSamplesMayBlock();
     } else {
@@ -305,19 +316,23 @@ MediaFormatReader::OnDemuxerInitDone(nsr
 
   bool audioActive = !!mDemuxer->GetNumberTracks(TrackInfo::kAudioTrack);
   if (audioActive) {
     mAudio.mTrackDemuxer = mDemuxer->GetTrackDemuxer(TrackInfo::kAudioTrack, 0);
     if (!mAudio.mTrackDemuxer) {
       mMetadataPromise.Reject(ReadMetadataFailureReason::METADATA_ERROR, __func__);
       return;
     }
+
     UniquePtr<TrackInfo> audioInfo = mAudio.mTrackDemuxer->GetInfo();
     // We actively ignore audio tracks that we know we can't play.
-    audioActive = audioInfo && audioInfo->IsValid();
+    audioActive = audioInfo && audioInfo->IsValid() &&
+                  (!platform ||
+                   platform->SupportsMimeType(audioInfo->mMimeType, nullptr));
+
     if (audioActive) {
       mInfo.mAudio = *audioInfo->GetAsAudioInfo();
       for (const MetadataTag& tag : audioInfo->mTags) {
         tags->Put(tag.mKey, tag.mValue);
       }
       mAudio.mCallback = new DecoderCallback(this, TrackInfo::kAudioTrack);
       mAudio.mTimeRanges = mAudio.mTrackDemuxer->GetBuffered();
       mTrackDemuxersMayBlock |= mAudio.mTrackDemuxer->GetSamplesMayBlock();