diff --git a/dom/media/MediaRecorder.cpp b/dom/media/MediaRecorder.cpp
index f88e3ef44b74..66ba1880aac9 100644
--- a/dom/media/MediaRecorder.cpp
+++ b/dom/media/MediaRecorder.cpp
@@ -474,6 +474,7 @@ class MediaRecorder::Session : public PrincipalChangeObserver<MediaStreamTrack>,
         mRunningState(RunningState::Idling) {
     MOZ_ASSERT(NS_IsMainThread());
 
+    aRecorder->GetMimeType(mMimeType);
     mMaxMemory = Preferences::GetUint("media.recorder.max_memory",
                                       MAX_ALLOW_MEMORY_BUFFER);
     mLastBlobTimeStamp = TimeStamp::Now();
@@ -950,9 +951,9 @@ class MediaRecorder::Session : public PrincipalChangeObserver<MediaStreamTrack>,
     // At this stage, the API doesn't allow UA to choose the output mimeType
     // format.
 
-    mEncoder = MediaEncoder::CreateEncoder(
-        mEncoderThread, NS_LITERAL_STRING(""), audioBitrate, videoBitrate,
-        aTrackTypes, aTrackRate);
+    mEncoder =
+        MediaEncoder::CreateEncoder(mEncoderThread, mMimeType, audioBitrate,
+                                    videoBitrate, aTrackTypes, aTrackRate);
 
     if (!mEncoder) {
       LOG(LogLevel::Error, ("Session.InitEncoder !mEncoder %p", this));
diff --git a/dom/media/encoder/MediaEncoder.cpp b/dom/media/encoder/MediaEncoder.cpp
index 0649adbbd406..dae45e4e5e14 100644
--- a/dom/media/encoder/MediaEncoder.cpp
+++ b/dom/media/encoder/MediaEncoder.cpp
@@ -637,33 +637,76 @@ already_AddRefed<MediaEncoder> MediaEncoder::CreateEncoder(
   }
 #ifdef MOZ_WEBM_ENCODER
   else if (MediaEncoder::IsWebMEncoderEnabled() &&
-           (aMIMEType.EqualsLiteral(VIDEO_WEBM) ||
-            (aTrackTypes & ContainerWriter::CREATE_VIDEO_TRACK))) {
+           aMIMEType.EqualsLiteral(VIDEO_WEBM)) {
     if (aTrackTypes & ContainerWriter::CREATE_AUDIO_TRACK &&
         MediaDecoder::IsOpusEnabled()) {
       audioEncoder = MakeAndAddRef<OpusTrackEncoder>(aTrackRate);
-      NS_ENSURE_TRUE(audioEncoder, nullptr);
     }
-    if (Preferences::GetBool("media.recorder.video.frame_drops", true)) {
-      videoEncoder = MakeAndAddRef<VP8TrackEncoder>(
-          driftCompensator, aTrackRate, FrameDroppingMode::ALLOW);
-    } else {
-      videoEncoder = MakeAndAddRef<VP8TrackEncoder>(
-          driftCompensator, aTrackRate, FrameDroppingMode::DISALLOW);
+    if (aTrackTypes & ContainerWriter::CREATE_VIDEO_TRACK) {
+      if (Preferences::GetBool("media.recorder.video.frame_drops", true)) {
+        videoEncoder = MakeAndAddRef<VP8TrackEncoder>(
+            driftCompensator, aTrackRate, FrameDroppingMode::ALLOW);
+      } else {
+        videoEncoder = MakeAndAddRef<VP8TrackEncoder>(
+            driftCompensator, aTrackRate, FrameDroppingMode::DISALLOW);
+      }
+    }
+    writer = MakeUnique<WebMWriter>(aTrackTypes);
+    mimeType = NS_LITERAL_STRING(VIDEO_WEBM);
+  } else if (MediaEncoder::IsWebMEncoderEnabled() &&
+             aMIMEType.EqualsLiteral(AUDIO_WEBM) &&
+             aTrackTypes & ContainerWriter::CREATE_AUDIO_TRACK) {
+    if (aTrackTypes & ContainerWriter::CREATE_AUDIO_TRACK &&
+        MediaDecoder::IsOpusEnabled()) {
+      audioEncoder = MakeAndAddRef<OpusTrackEncoder>(aTrackRate);
+    }
+    if (aTrackTypes & ContainerWriter::CREATE_VIDEO_TRACK) {
+      if (Preferences::GetBool("media.recorder.video.frame_drops", true)) {
+        videoEncoder = MakeAndAddRef<VP8TrackEncoder>(
+            driftCompensator, aTrackRate, FrameDroppingMode::ALLOW);
+      } else {
+        videoEncoder = MakeAndAddRef<VP8TrackEncoder>(
+            driftCompensator, aTrackRate, FrameDroppingMode::DISALLOW);
+      }
+      mimeType = NS_LITERAL_STRING(VIDEO_WEBM);
+    } else {
+      mimeType = NS_LITERAL_STRING(AUDIO_WEBM);
+    }
+    writer = MakeUnique<WebMWriter>(aTrackTypes);
+  }
+#endif  // MOZ_WEBM_ENCODER
+  else if (MediaDecoder::IsOggEnabled() && MediaDecoder::IsOpusEnabled() &&
+           aMIMEType.EqualsLiteral(AUDIO_OGG) &&
+           aTrackTypes & ContainerWriter::CREATE_AUDIO_TRACK) {
+    writer = MakeUnique<OggWriter>();
+    audioEncoder = MakeAndAddRef<OpusTrackEncoder>(aTrackRate);
+    mimeType = NS_LITERAL_STRING(AUDIO_OGG);
+  }
+#ifdef MOZ_WEBM_ENCODER
+  else if (MediaEncoder::IsWebMEncoderEnabled() &&
+           (aTrackTypes & ContainerWriter::CREATE_VIDEO_TRACK ||
+            !MediaDecoder::IsOggEnabled())) {
+    if (aTrackTypes & ContainerWriter::CREATE_AUDIO_TRACK &&
+        MediaDecoder::IsOpusEnabled()) {
+      audioEncoder = MakeAndAddRef<OpusTrackEncoder>(aTrackRate);
+    }
+    if (aTrackTypes & ContainerWriter::CREATE_VIDEO_TRACK) {
+      if (Preferences::GetBool("media.recorder.video.frame_drops", true)) {
+        videoEncoder = MakeAndAddRef<VP8TrackEncoder>(
+            driftCompensator, aTrackRate, FrameDroppingMode::ALLOW);
+      } else {
+        videoEncoder = MakeAndAddRef<VP8TrackEncoder>(
+            driftCompensator, aTrackRate, FrameDroppingMode::DISALLOW);
+      }
     }
     writer = MakeUnique<WebMWriter>(aTrackTypes);
-    NS_ENSURE_TRUE(writer, nullptr);
-    NS_ENSURE_TRUE(videoEncoder, nullptr);
     mimeType = NS_LITERAL_STRING(VIDEO_WEBM);
   }
 #endif  // MOZ_WEBM_ENCODER
   else if (MediaDecoder::IsOggEnabled() && MediaDecoder::IsOpusEnabled() &&
-           (aMIMEType.EqualsLiteral(AUDIO_OGG) ||
-            (aTrackTypes & ContainerWriter::CREATE_AUDIO_TRACK))) {
+           aTrackTypes & ContainerWriter::CREATE_AUDIO_TRACK) {
     writer = MakeUnique<OggWriter>();
     audioEncoder = MakeAndAddRef<OpusTrackEncoder>(aTrackRate);
-    NS_ENSURE_TRUE(writer, nullptr);
-    NS_ENSURE_TRUE(audioEncoder, nullptr);
     mimeType = NS_LITERAL_STRING(AUDIO_OGG);
   } else {
     LOG(LogLevel::Error,
@@ -672,7 +715,8 @@ already_AddRefed<MediaEncoder> MediaEncoder::CreateEncoder(
   }
 
   LOG(LogLevel::Info,
-      ("Create encoder result:a[%p](%u bps) v[%p](%u bps) w[%p] mimeType = %s.",
+      ("Create encoder result:a[%p](%u bps) v[%p](%u bps) w[%p] mimeType = "
+       "%s.",
        audioEncoder.get(), aAudioBitrate, videoEncoder.get(), aVideoBitrate,
        writer.get(), NS_ConvertUTF16toUTF8(mimeType).get()));
 
@@ -801,7 +845,8 @@ nsresult MediaEncoder::GetEncodedData(
     }
   }
 
-  // In audio only or video only case, let unavailable track's flag to be true.
+  // In audio only or video only case, let unavailable track's flag to be
+  // true.
   bool isAudioCompleted = !mAudioEncoder || mAudioEncoder->IsEncodingComplete();
   bool isVideoCompleted = !mVideoEncoder || mVideoEncoder->IsEncodingComplete();
   rv = mWriter->GetContainerData(