diff --git a/dom/media/mp4/MP4Demuxer.cpp b/dom/media/mp4/MP4Demuxer.cpp
index 569b7896c691..4e82485f73bd 100644
--- a/dom/media/mp4/MP4Demuxer.cpp
+++ b/dom/media/mp4/MP4Demuxer.cpp
@@ -414,10 +414,11 @@ already_AddRefed<MediaRawData> MP4TrackDemuxer::GetNextSample() {
     if (mType == kH264 && !sample->mCrypto.IsEncrypted()) {
       H264::FrameType type = H264::GetFrameType(sample);
       switch (type) {
-        case H264::FrameType::I_FRAME:
-          [[fallthrough]];
+        case H264::FrameType::I_FRAME_IDR:
+        case H264::FrameType::I_FRAME_OTHER:
         case H264::FrameType::OTHER: {
-          bool keyframe = type == H264::FrameType::I_FRAME;
+          bool keyframe = type == H264::FrameType::I_FRAME_OTHER ||
+                          type == H264::FrameType::I_FRAME_IDR;
           if (sample->mKeyframe != keyframe) {
             NS_WARNING(nsPrintfCString("Frame incorrectly marked as %skeyframe "
                                        "@ pts:%" PRId64 " dur:%" PRId64
diff --git a/dom/media/platforms/agnostic/bytestreams/H264.cpp b/dom/media/platforms/agnostic/bytestreams/H264.cpp
index 226931463a49..e3c60bb35da8 100644
--- a/dom/media/platforms/agnostic/bytestreams/H264.cpp
+++ b/dom/media/platforms/agnostic/bytestreams/H264.cpp
@@ -958,18 +958,18 @@ uint32_t H264::ComputeMaxRefFrames(const mozilla::MediaByteBuffer* aExtraData) {
     int8_t nalType = AssertedCast<int8_t>(*p & 0x1f);
     if (nalType == H264_NAL_IDR_SLICE) {
       // IDR NAL.
-      return FrameType::I_FRAME;
+      return FrameType::I_FRAME_IDR;
     }
     if (nalType == H264_NAL_SEI) {
       RefPtr<mozilla::MediaByteBuffer> decodedNAL = DecodeNALUnit(p, nalLen);
       SEIRecoveryData data;
       if (DecodeRecoverySEI(decodedNAL, data)) {
-        return FrameType::I_FRAME;
+        return FrameType::I_FRAME_OTHER;
       }
     } else if (nalType == H264_NAL_SLICE) {
       RefPtr<mozilla::MediaByteBuffer> decodedNAL = DecodeNALUnit(p, nalLen);
       if (DecodeISlice(decodedNAL)) {
-        return FrameType::I_FRAME;
+        return FrameType::I_FRAME_OTHER;
       }
     }
   }
diff --git a/dom/media/platforms/agnostic/bytestreams/H264.h b/dom/media/platforms/agnostic/bytestreams/H264.h
index c62d6b15e135..bcf01f0555cc 100644
--- a/dom/media/platforms/agnostic/bytestreams/H264.h
+++ b/dom/media/platforms/agnostic/bytestreams/H264.h
@@ -516,7 +516,14 @@ class H264 {
       const mozilla::MediaByteBuffer* aExtraData);
 
   enum class FrameType {
-    I_FRAME,
+    // IDR is a special iframe, according to the spec T-REC-H.264-202408, 3.69 :
+    // "An IDR picture causes the decoding process to mark all reference
+    // pictures as "unused for reference" immediately after the decoding of the
+    // IDR picture. All coded pictures that follow an IDR picture in decoding
+    // order can be decoded without inter prediction from any picture that
+    // precedes the IDR picture in decoding order."
+    I_FRAME_IDR,
+    I_FRAME_OTHER,
     OTHER,
     INVALID,
   };
diff --git a/dom/media/platforms/wrappers/MediaChangeMonitor.cpp b/dom/media/platforms/wrappers/MediaChangeMonitor.cpp
index 1840a99d9aed..46fd2be056be 100644
--- a/dom/media/platforms/wrappers/MediaChangeMonitor.cpp
+++ b/dom/media/platforms/wrappers/MediaChangeMonitor.cpp
@@ -74,10 +74,17 @@ static bool IsBeingProfiledOrLogEnabled() {
 
 class H264ChangeMonitor : public MediaChangeMonitor::CodecChangeMonitor {
  public:
-  explicit H264ChangeMonitor(const VideoInfo& aInfo, bool aFullParsing)
-      : mCurrentConfig(aInfo), mFullParsing(aFullParsing) {
+  explicit H264ChangeMonitor(const CreateDecoderParams& aParams)
+      : mCurrentConfig(aParams.VideoConfig()),
+        mFullParsing(aParams.mOptions.contains(
+            CreateDecoderParams::Option::FullH264Parsing))
+#ifdef MOZ_WMF_MEDIA_ENGINE
+        ,
+        mIsMediaEnginePlayback(aParams.mMediaEngineId.isSome())
+#endif
+  {
     if (CanBeInstantiated()) {
-      UpdateConfigFromExtraData(aInfo.mExtraData);
+      UpdateConfigFromExtraData(mCurrentConfig.mExtraData);
       auto avcc = AVCCConfig::Parse(mCurrentConfig.mExtraData);
       if (avcc.isOk() && avcc.unwrap().NALUSize() != 4) {
         // `CheckForChange()` will use `AnnexB::ConvertSampleToAVCC()` to change
@@ -169,14 +176,21 @@ class H264ChangeMonitor : public MediaChangeMonitor::CodecChangeMonitor {
     aSample->mTrackInfo = mTrackInfo;
 
     bool appendExtradata = aNeedKeyFrame;
-    if (aSample->mCrypto.IsEncrypted() && !mReceivedFirstEncryptedSample) {
-      LOG("Detected first encrypted sample [%" PRId64 ",%" PRId64
-          "], keyframe=%d",
-          aSample->mTime.ToMicroseconds(),
-          aSample->GetEndTime().ToMicroseconds(), aSample->mKeyframe);
-      mReceivedFirstEncryptedSample = true;
-      appendExtradata = true;
+#ifdef MOZ_WMF_MEDIA_ENGINE
+    // The error SPR_E_INVALID_H264_SLICE_HEADERS is caused by the media engine
+    // being unable to handle an IDR frame without a valid SPS. Therefore, we
+    // ensure that SPS should always be presented in the bytestream for all IDR
+    // frames.
+    if (mIsMediaEnginePlayback &&
+        H264::GetFrameType(aSample) == H264::FrameType::I_FRAME_IDR) {
+      RefPtr<MediaByteBuffer> extradata = H264::ExtractExtraData(aSample);
+      appendExtradata = aNeedKeyFrame || !H264::HasSPS(extradata);
+      LOG("%s need to append extradata for IDR sample [%" PRId64 ",%" PRId64
+          "]",
+          appendExtradata ? "Do" : "No", aSample->mTime.ToMicroseconds(),
+          aSample->GetEndTime().ToMicroseconds());
     }
+#endif
 
     if (aConversion == MediaDataDecoder::ConversionRequired::kNeedAnnexB) {
       auto res = AnnexB::ConvertAVCCSampleToAnnexB(aSample, appendExtradata);
@@ -189,8 +203,6 @@ class H264ChangeMonitor : public MediaChangeMonitor::CodecChangeMonitor {
     return NS_OK;
   }
 
-  void Flush() override { mReceivedFirstEncryptedSample = false; }
-
  private:
   void UpdateConfigFromExtraData(MediaByteBuffer* aExtraData) {
     SPSData spsdata;
@@ -224,14 +236,13 @@ class H264ChangeMonitor : public MediaChangeMonitor::CodecChangeMonitor {
   VideoInfo mCurrentConfig;
   uint32_t mStreamID = 0;
   const bool mFullParsing;
+#ifdef MOZ_WMF_MEDIA_ENGINE
+  // True if the playback is performed by Windows Media Foundation Engine.
+  const bool mIsMediaEnginePlayback;
+#endif
   bool mGotSPS = false;
   RefPtr<TrackInfoSharedPtr> mTrackInfo;
   RefPtr<MediaByteBuffer> mPreviousExtraData;
-
-  // This ensures the first encrypted sample always includes all necessary
-  // information for decoding, as some decoders, such as MediaEngine, require
-  // SPS/PPS to be appended during the clearlead-to-encrypted transition.
-  bool mReceivedFirstEncryptedSample = false;
 };
 
 class HEVCChangeMonitor : public MediaChangeMonitor::CodecChangeMonitor {
@@ -820,9 +831,7 @@ RefPtr<PlatformDecoderModule::CreateDecoderPromise> MediaChangeMonitor::Create(
       changeMonitor = MakeUnique<HEVCChangeMonitor>(config);
     } else {
       MOZ_ASSERT(MP4Decoder::IsH264(config.mMimeType));
-      changeMonitor = MakeUnique<H264ChangeMonitor>(
-          config, aParams.mOptions.contains(
-                      CreateDecoderParams::Option::FullH264Parsing));
+      changeMonitor = MakeUnique<H264ChangeMonitor>(aParams);
     }
   } else {
     MOZ_ASSERT(MP4Decoder::IsAAC(aParams.AudioConfig().mMimeType));