diff --git a/dom/media/ipc/RemoteDecoderModule.cpp b/dom/media/ipc/RemoteDecoderModule.cpp
index dfbb2305091a..af0827d0ca94 100644
--- a/dom/media/ipc/RemoteDecoderModule.cpp
+++ b/dom/media/ipc/RemoteDecoderModule.cpp
@@ -19,6 +19,7 @@
 #include "RemoteMediaDataDecoder.h"
 #include "RemoteVideoDecoder.h"
 #include "OpusDecoder.h"
+#include "VideoUtils.h"
 #include "VorbisDecoder.h"
 #include "WAVDecoder.h"
 
@@ -105,6 +106,16 @@ already_AddRefed<MediaDataDecoder> RemoteDecoderModule::CreateAudioDecoder(
     return nullptr;
   }
 
+  // OpusDataDecoder will check this option to provide the same info
+  // that IsDefaultPlaybackDeviceMono provides.  We want to avoid calls
+  // to IsDefaultPlaybackDeviceMono on RDD because initializing audio
+  // backends on RDD will be blocked by the sandbox.
+  CreateDecoderParams::OptionSet options(aParams.mOptions);
+  if (OpusDataDecoder::IsOpus(aParams.mConfig.mMimeType) &&
+      IsDefaultPlaybackDeviceMono()) {
+    options += CreateDecoderParams::Option::DefaultPlaybackDeviceMono;
+  }
+
   RefPtr<RemoteAudioDecoderChild> child = new RemoteAudioDecoderChild();
   MediaResult result(NS_OK);
   // We can use child as a ref here because this is a sync dispatch. In
@@ -116,7 +127,7 @@ already_AddRefed<MediaDataDecoder> RemoteDecoderModule::CreateAudioDecoder(
   // thread during this single dispatch.
   RefPtr<Runnable> task =
       NS_NewRunnableFunction("RemoteDecoderModule::CreateAudioDecoder", [&]() {
-        result = child->InitIPDL(aParams.AudioConfig(), aParams.mOptions);
+        result = child->InitIPDL(aParams.AudioConfig(), options);
         if (NS_FAILED(result)) {
           // Release RemoteAudioDecoderChild here, while we're on
           // manager thread.  Don't just let the RefPtr go out of scope.
diff --git a/dom/media/platforms/PlatformDecoderModule.h b/dom/media/platforms/PlatformDecoderModule.h
index feba83226fcf..a5ba14775cbb 100644
--- a/dom/media/platforms/PlatformDecoderModule.h
+++ b/dom/media/platforms/PlatformDecoderModule.h
@@ -53,6 +53,8 @@ struct MOZ_STACK_CLASS CreateDecoderParams final {
                                   // initialization data are dropped. Pass this
                                   // option to raise an error if frames are
                                   // delivered before initialization data.
+    DefaultPlaybackDeviceMono,    // Currently only used by Opus on RDD to avoid
+                                  // initialization of audio backends on RDD
 
     SENTINEL  // one past the last valid value
   };
diff --git a/dom/media/platforms/agnostic/AgnosticDecoderModule.cpp b/dom/media/platforms/agnostic/AgnosticDecoderModule.cpp
index 8ff8acbccdcb..c23466dc22a9 100644
--- a/dom/media/platforms/agnostic/AgnosticDecoderModule.cpp
+++ b/dom/media/platforms/agnostic/AgnosticDecoderModule.cpp
@@ -88,7 +88,14 @@ already_AddRefed<MediaDataDecoder> AgnosticDecoderModule::CreateAudioDecoder(
   if (VorbisDataDecoder::IsVorbis(config.mMimeType)) {
     m = new VorbisDataDecoder(aParams);
   } else if (OpusDataDecoder::IsOpus(config.mMimeType)) {
-    m = new OpusDataDecoder(aParams);
+    CreateDecoderParams params(aParams);
+    // Check IsDefaultPlaybackDeviceMono here and set the option in
+    // mOptions so OpusDataDecoder doesn't have to do it later (in case
+    // it is running on RDD).
+    if (IsDefaultPlaybackDeviceMono()) {
+      params.mOptions += CreateDecoderParams::Option::DefaultPlaybackDeviceMono;
+    }
+    m = new OpusDataDecoder(params);
   } else if (WaveDataDecoder::IsWave(config.mMimeType)) {
     m = new WaveDataDecoder(aParams);
   }
diff --git a/dom/media/platforms/agnostic/OpusDecoder.cpp b/dom/media/platforms/agnostic/OpusDecoder.cpp
index 1808a7415195..b53387c53fc3 100644
--- a/dom/media/platforms/agnostic/OpusDecoder.cpp
+++ b/dom/media/platforms/agnostic/OpusDecoder.cpp
@@ -35,7 +35,9 @@ OpusDataDecoder::OpusDataDecoder(const CreateDecoderParams& aParams)
       mDecodedHeader(false),
       mPaddingDiscarded(false),
       mFrames(0),
-      mChannelMap(AudioConfig::ChannelLayout::UNKNOWN_MAP) {}
+      mChannelMap(AudioConfig::ChannelLayout::UNKNOWN_MAP),
+      mDefaultPlaybackDeviceMono(aParams.mOptions.contains(
+          CreateDecoderParams::Option::DefaultPlaybackDeviceMono)) {}
 
 OpusDataDecoder::~OpusDataDecoder() {
   if (mOpusDecoder) {
@@ -99,8 +101,7 @@ RefPtr<MediaDataDecoder::InitPromise> OpusDataDecoder::Init() {
   // needs to be disabled when the output is downmixed to mono. Playback number
   // of channels are set in AudioSink, using the same method
   // `DecideAudioPlaybackChannels()`, and triggers downmix if needed.
-  if (IsDefaultPlaybackDeviceMono() ||
-      DecideAudioPlaybackChannels(mInfo) == 1) {
+  if (mDefaultPlaybackDeviceMono || DecideAudioPlaybackChannels(mInfo) == 1) {
     opus_multistream_decoder_ctl(mOpusDecoder,
                                  OPUS_SET_PHASE_INVERSION_DISABLED(1));
   }
diff --git a/dom/media/platforms/agnostic/OpusDecoder.h b/dom/media/platforms/agnostic/OpusDecoder.h
index 91c02f03ae99..c134ef1e6f4a 100644
--- a/dom/media/platforms/agnostic/OpusDecoder.h
+++ b/dom/media/platforms/agnostic/OpusDecoder.h
@@ -68,6 +68,7 @@ class OpusDataDecoder : public MediaDataDecoder,
   Maybe<int64_t> mLastFrameTime;
   AutoTArray<uint8_t, 8> mMappingTable;
   AudioConfig::ChannelLayout::ChannelMap mChannelMap;
+  bool mDefaultPlaybackDeviceMono;
 };
 
 }  // namespace mozilla