/* -*- Mode: C++; tab-width: 2; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
/* vim:set ts=2 sw=2 sts=2 et cindent: */
/* This Source Code Form is subject to the terms of the Mozilla Public
 * 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/. */

#include "MediaChangeMonitor.h"

#include "AnnexB.h"
#include "H264.h"
#include "GeckoProfiler.h"
#include "ImageContainer.h"
#include "MP4Decoder.h"
#include "MediaInfo.h"
#include "PDMFactory.h"
#include "VPXDecoder.h"
#include "mozilla/ProfilerMarkers.h"
#include "mozilla/StaticPrefs_media.h"
#include "mozilla/TaskQueue.h"

namespace mozilla {

// H264ChangeMonitor is used to ensure that only AVCC or AnnexB is fed to the
// underlying MediaDataDecoder. The H264ChangeMonitor allows playback of content
// where the SPS NAL may not be provided in the init segment (e.g. AVC3 or Annex
// B) H264ChangeMonitor will monitor the input data, and will delay creation of
// the MediaDataDecoder until a SPS and PPS NALs have been extracted.

class H264ChangeMonitor : public MediaChangeMonitor::CodecChangeMonitor {
 public:
  explicit H264ChangeMonitor(const VideoInfo& aInfo, bool aFullParsing)
      : mCurrentConfig(aInfo), mFullParsing(aFullParsing) {
    if (CanBeInstantiated()) {
      UpdateConfigFromExtraData(aInfo.mExtraData);
    }
  }

  bool CanBeInstantiated() const override {
    return H264::HasSPS(mCurrentConfig.mExtraData);
  }

  MediaResult CheckForChange(MediaRawData* aSample) override {
    // To be usable we need to convert the sample to 4 bytes NAL size AVCC.
    if (!AnnexB::ConvertSampleToAVCC(aSample)) {
      // We need AVCC content to be able to later parse the SPS.
      // This is a no-op if the data is already AVCC.
      return MediaResult(NS_ERROR_OUT_OF_MEMORY,
                         RESULT_DETAIL("ConvertSampleToAVCC"));
    }

    if (!AnnexB::IsAVCC(aSample)) {
      return MediaResult(NS_ERROR_DOM_MEDIA_FATAL_ERR,
                         RESULT_DETAIL("Invalid H264 content"));
    }

    RefPtr<MediaByteBuffer> extra_data =
        aSample->mKeyframe || !mGotSPS || mFullParsing
            ? H264::ExtractExtraData(aSample)
            : nullptr;

    if (!H264::HasSPS(extra_data) && !H264::HasSPS(mCurrentConfig.mExtraData)) {
      // We don't have inband data and the original config didn't contain a SPS.
      // We can't decode this content.
      return NS_ERROR_NOT_INITIALIZED;
    }

    mGotSPS = true;

    if (!H264::HasSPS(extra_data)) {
      // This sample doesn't contain inband SPS/PPS
      // We now check if the out of band one has changed.
      // This scenario can currently only occur on Android with devices that can
      // recycle a decoder.
      bool hasOutOfBandExtraData = H264::HasSPS(aSample->mExtraData);
      if (!hasOutOfBandExtraData || !mPreviousExtraData ||
          H264::CompareExtraData(aSample->mExtraData, mPreviousExtraData)) {
        if (hasOutOfBandExtraData && !mPreviousExtraData) {
          // We are decoding the first sample, store the out of band sample's
          // extradata so that we can check for future change.
          mPreviousExtraData = aSample->mExtraData;
        }
        return NS_OK;
      }
      extra_data = aSample->mExtraData;
    } else if (H264::CompareExtraData(extra_data, mCurrentConfig.mExtraData)) {
      return NS_OK;
    }

    // Store the sample's extradata so we don't trigger a false positive
    // with the out of band test on the next sample.
    mPreviousExtraData = aSample->mExtraData;
    UpdateConfigFromExtraData(extra_data);

    PROFILER_MARKER_TEXT("H264 Stream Change", MEDIA_PLAYBACK, {},
                         "H264ChangeMonitor::CheckForChange has detected a "
                         "change in the stream and will request a new decoder");
    return NS_ERROR_DOM_MEDIA_NEED_NEW_DECODER;
  }

  const TrackInfo& Config() const override { return mCurrentConfig; }

  MediaResult PrepareSample(MediaDataDecoder::ConversionRequired aConversion,
                            MediaRawData* aSample,
                            bool aNeedKeyFrame) override {
    MOZ_DIAGNOSTIC_ASSERT(
        aConversion == MediaDataDecoder::ConversionRequired::kNeedAnnexB ||
            aConversion == MediaDataDecoder::ConversionRequired::kNeedAVCC,
        "Conversion must be either AVCC or AnnexB");

    aSample->mExtraData = mCurrentConfig.mExtraData;
    aSample->mTrackInfo = mTrackInfo;

    if (aConversion == MediaDataDecoder::ConversionRequired::kNeedAnnexB) {
      auto res = AnnexB::ConvertSampleToAnnexB(aSample, aNeedKeyFrame);
      if (res.isErr()) {
        return MediaResult(res.unwrapErr(),
                           RESULT_DETAIL("ConvertSampleToAnnexB"));
      }
    }

    return NS_OK;
  }

 private:
  void UpdateConfigFromExtraData(MediaByteBuffer* aExtraData) {
    SPSData spsdata;
    if (H264::DecodeSPSFromExtraData(aExtraData, spsdata) &&
        spsdata.pic_width > 0 && spsdata.pic_height > 0) {
      H264::EnsureSPSIsSane(spsdata);
      mCurrentConfig.mImage.width = spsdata.pic_width;
      mCurrentConfig.mImage.height = spsdata.pic_height;
      mCurrentConfig.mDisplay.width = spsdata.display_width;
      mCurrentConfig.mDisplay.height = spsdata.display_height;
      mCurrentConfig.mColorDepth = spsdata.ColorDepth();
      mCurrentConfig.mColorSpace = spsdata.ColorSpace();
      mCurrentConfig.mColorRange = spsdata.video_full_range_flag
                                       ? gfx::ColorRange::FULL
                                       : gfx::ColorRange::LIMITED;
    }
    mCurrentConfig.mExtraData = aExtraData;
    mTrackInfo = new TrackInfoSharedPtr(mCurrentConfig, mStreamID++);
  }

  VideoInfo mCurrentConfig;
  uint32_t mStreamID = 0;
  const bool mFullParsing;
  bool mGotSPS = false;
  RefPtr<TrackInfoSharedPtr> mTrackInfo;
  RefPtr<MediaByteBuffer> mPreviousExtraData;
};

class VPXChangeMonitor : public MediaChangeMonitor::CodecChangeMonitor {
 public:
  explicit VPXChangeMonitor(const VideoInfo& aInfo)
      : mCurrentConfig(aInfo),
        mCodec(VPXDecoder::IsVP8(aInfo.mMimeType) ? VPXDecoder::Codec::VP8
                                                  : VPXDecoder::Codec::VP9) {
    mTrackInfo = new TrackInfoSharedPtr(mCurrentConfig, mStreamID++);
  }

  bool CanBeInstantiated() const override {
    // We want to see at least one sample before we create a decoder so that we
    // can create the vpcC content on mCurrentConfig.mExtraData.
    return mCodec == VPXDecoder::Codec::VP8 || mInfo ||
           mCurrentConfig.mCrypto.IsEncrypted();
  }

  MediaResult CheckForChange(MediaRawData* aSample) override {
    // Don't look at encrypted content.
    if (aSample->mCrypto.IsEncrypted()) {
      return NS_OK;
    }
    auto dataSpan = Span<const uint8_t>(aSample->Data(), aSample->Size());

    // We don't trust the keyframe flag as set on the MediaRawData.
    VPXDecoder::VPXStreamInfo info;
    if (!VPXDecoder::GetStreamInfo(dataSpan, info, mCodec)) {
      return NS_ERROR_DOM_MEDIA_DECODE_ERR;
    }
    // For both VP8 and VP9, we only look for resolution changes
    // on keyframes. Other resolution changes are invalid.
    if (!info.mKeyFrame) {
      return NS_OK;
    }

    nsresult rv = NS_OK;
    if (mInfo) {
      if (mInfo.ref().IsCompatible(info)) {
        return rv;
      }
      // We can't properly determine the image rect once we've had a resolution
      // change.
      mCurrentConfig.ResetImageRect();
      PROFILER_MARKER_TEXT(
          "VPX Stream Change", MEDIA_PLAYBACK, {},
          "VPXChangeMonitor::CheckForChange has detected a change in the "
          "stream and will request a new decoder");
      rv = NS_ERROR_DOM_MEDIA_NEED_NEW_DECODER;
    } else if (mCurrentConfig.mImage != info.mImage ||
               mCurrentConfig.mDisplay != info.mDisplay) {
      PROFILER_MARKER_TEXT("VPX Stream Init Discrepancy", MEDIA_PLAYBACK, {},
                           "VPXChangeMonitor::CheckForChange has detected a "
                           "discrepancy between initialization data and stream "
                           "content and will request a new decoder");
      rv = NS_ERROR_DOM_MEDIA_NEED_NEW_DECODER;
    }
    mInfo = Some(info);
    mCurrentConfig.mImage = info.mImage;
    mCurrentConfig.mDisplay = info.mDisplay;
    mCurrentConfig.mColorDepth = gfx::ColorDepthForBitDepth(info.mBitDepth);
    mCurrentConfig.mColorSpace = info.ColorSpace();
    mCurrentConfig.mColorRange = info.ColorRange();
    if (mCodec == VPXDecoder::Codec::VP9) {
      VPXDecoder::GetVPCCBox(mCurrentConfig.mExtraData, info);
    }
    mTrackInfo = new TrackInfoSharedPtr(mCurrentConfig, mStreamID++);

    return rv;
  }

  const TrackInfo& Config() const override { return mCurrentConfig; }

  MediaResult PrepareSample(MediaDataDecoder::ConversionRequired aConversion,
                            MediaRawData* aSample,
                            bool aNeedKeyFrame) override {
    aSample->mTrackInfo = mTrackInfo;

    return NS_OK;
  }

 private:
  VideoInfo mCurrentConfig;
  const VPXDecoder::Codec mCodec;
  Maybe<VPXDecoder::VPXStreamInfo> mInfo;
  uint32_t mStreamID = 0;
  RefPtr<TrackInfoSharedPtr> mTrackInfo;
};

MediaChangeMonitor::MediaChangeMonitor(
    PlatformDecoderModule* aPDM,
    UniquePtr<CodecChangeMonitor>&& aCodecChangeMonitor,
    MediaDataDecoder* aDecoder, const CreateDecoderParams& aParams)
    : mChangeMonitor(std::move(aCodecChangeMonitor)),
      mPDM(aPDM),
      mCurrentConfig(aParams.VideoConfig()),
      mDecoder(aDecoder),
      mParams(aParams) {}

/* static */
RefPtr<PlatformDecoderModule::CreateDecoderPromise> MediaChangeMonitor::Create(
    PlatformDecoderModule* aPDM, const CreateDecoderParams& aParams) {
  UniquePtr<CodecChangeMonitor> changeMonitor;
  const VideoInfo& currentConfig = aParams.VideoConfig();
  if (VPXDecoder::IsVPX(currentConfig.mMimeType)) {
    changeMonitor = MakeUnique<VPXChangeMonitor>(currentConfig);
  } else {
    MOZ_ASSERT(MP4Decoder::IsH264(currentConfig.mMimeType));
    changeMonitor = MakeUnique<H264ChangeMonitor>(
        currentConfig, aParams.mOptions.contains(
                           CreateDecoderParams::Option::FullH264Parsing));
  }

  if (!changeMonitor->CanBeInstantiated()) {
    // nothing found yet, will try again later
    return PlatformDecoderModule::CreateDecoderPromise::CreateAndResolve(
        new MediaChangeMonitor(aPDM, std::move(changeMonitor), nullptr,
                               aParams),
        __func__);
  }

  RefPtr<PlatformDecoderModule::CreateDecoderPromise> p =
      aPDM->AsyncCreateDecoder(aParams)->Then(
          GetCurrentSerialEventTarget(), __func__,
          [params = CreateDecoderParamsForAsync(aParams), pdm = RefPtr{aPDM},
           changeMonitor = std::move(changeMonitor)](
              RefPtr<MediaDataDecoder>&& aDecoder) mutable {
            RefPtr<MediaDataDecoder> decoder = new MediaChangeMonitor(
                pdm, std::move(changeMonitor), aDecoder, params);
            return PlatformDecoderModule::CreateDecoderPromise::
                CreateAndResolve(decoder, __func__);
          },
          [](MediaResult aError) {
            return PlatformDecoderModule::CreateDecoderPromise::CreateAndReject(
                aError, __func__);
          });
  return p;
}

MediaChangeMonitor::~MediaChangeMonitor() = default;

RefPtr<MediaDataDecoder::InitPromise> MediaChangeMonitor::Init() {
  mThread = GetCurrentSerialEventTarget();
  if (mDecoder) {
    RefPtr<InitPromise> p = mInitPromise.Ensure(__func__);
    RefPtr<MediaChangeMonitor> self = this;
    mDecoder->Init()
        ->Then(GetCurrentSerialEventTarget(), __func__,
               [self, this](InitPromise::ResolveOrRejectValue&& aValue) {
                 mInitPromiseRequest.Complete();
                 if (aValue.IsResolve()) {
                   mDecoderInitialized = true;
                   mConversionRequired = Some(mDecoder->NeedsConversion());
                   mCanRecycleDecoder = Some(CanRecycleDecoder());
                 }
                 return mInitPromise.ResolveOrRejectIfExists(std::move(aValue),
                                                             __func__);
               })
        ->Track(mInitPromiseRequest);
    return p;
  }

  // We haven't been able to initialize a decoder due to missing
  // extradata.
  return MediaDataDecoder::InitPromise::CreateAndResolve(TrackType::kVideoTrack,
                                                         __func__);
}

RefPtr<MediaDataDecoder::DecodePromise> MediaChangeMonitor::Decode(
    MediaRawData* aSample) {
  AssertOnThread();
  MOZ_RELEASE_ASSERT(mFlushPromise.IsEmpty(),
                     "Flush operation didn't complete");

  MOZ_RELEASE_ASSERT(
      !mDecodePromiseRequest.Exists() && !mInitPromiseRequest.Exists(),
      "Can't request a new decode until previous one completed");

  MediaResult rv = CheckForChange(aSample);

  if (rv == NS_ERROR_NOT_INITIALIZED) {
    // We are missing the required init data to create the decoder.
    if (mParams.mOptions.contains(
            CreateDecoderParams::Option::ErrorIfNoInitializationData)) {
      // This frame can't be decoded and should be treated as an error.
      return DecodePromise::CreateAndReject(rv, __func__);
    }
    // Swallow the frame, and await delivery of init data.
    return DecodePromise::CreateAndResolve(DecodedData(), __func__);
  }
  if (rv == NS_ERROR_DOM_MEDIA_INITIALIZING_DECODER) {
    // The decoder is pending initialization.
    RefPtr<DecodePromise> p = mDecodePromise.Ensure(__func__);
    return p;
  }

  if (NS_FAILED(rv)) {
    return DecodePromise::CreateAndReject(rv, __func__);
  }

  if (mNeedKeyframe && !aSample->mKeyframe) {
    return DecodePromise::CreateAndResolve(DecodedData(), __func__);
  }

  rv = mChangeMonitor->PrepareSample(*mConversionRequired, aSample,
                                     mNeedKeyframe);
  if (NS_FAILED(rv)) {
    return DecodePromise::CreateAndReject(rv, __func__);
  }

  mNeedKeyframe = false;

  return mDecoder->Decode(aSample);
}

RefPtr<MediaDataDecoder::FlushPromise> MediaChangeMonitor::Flush() {
  AssertOnThread();
  mDecodePromiseRequest.DisconnectIfExists();
  mDecodePromise.RejectIfExists(NS_ERROR_DOM_MEDIA_CANCELED, __func__);
  mNeedKeyframe = true;
  mPendingFrames.Clear();

  MOZ_RELEASE_ASSERT(mFlushPromise.IsEmpty(), "Previous flush didn't complete");

  /*
    When we detect a change of content in the byte stream, we first drain the
    current decoder (1), flush (2), shut it down (3) create a new decoder (4)
    and initialize it (5). It is possible for MediaChangeMonitor::Flush to be
    called during any of those times. If during (1):
      - mDrainRequest will not be empty.
      - The old decoder can still be used, with the current extradata as
    stored in mCurrentConfig.mExtraData.

    If during (2):
      - mFlushRequest will not be empty.
      - The old decoder can still be used, with the current extradata as
    stored in mCurrentConfig.mExtraData.

    If during (3):
      - mShutdownRequest won't be empty.
      - mDecoder is empty.
      - The old decoder is no longer referenced by the MediaChangeMonitor.

    If during (4):
      - mDecoderRequest won't be empty.
      - mDecoder is not set. Steps will continue to (5) to set and initialize it

    If during (5):
      - mInitPromiseRequest won't be empty.
      - mDecoder is set but not usable yet.
  */

  if (mDrainRequest.Exists() || mFlushRequest.Exists() ||
      mShutdownRequest.Exists() || mDecoderRequest.Exists() ||
      mInitPromiseRequest.Exists()) {
    // We let the current decoder complete and will resume after.
    RefPtr<FlushPromise> p = mFlushPromise.Ensure(__func__);
    return p;
  }
  if (mDecoder && mDecoderInitialized) {
    return mDecoder->Flush();
  }
  return FlushPromise::CreateAndResolve(true, __func__);
}

RefPtr<MediaDataDecoder::DecodePromise> MediaChangeMonitor::Drain() {
  AssertOnThread();
  MOZ_RELEASE_ASSERT(!mDrainRequest.Exists());
  mNeedKeyframe = true;
  if (mDecoder) {
    return mDecoder->Drain();
  }
  return DecodePromise::CreateAndResolve(DecodedData(), __func__);
}

RefPtr<ShutdownPromise> MediaChangeMonitor::Shutdown() {
  AssertOnThread();
  mInitPromiseRequest.DisconnectIfExists();
  mInitPromise.RejectIfExists(NS_ERROR_DOM_MEDIA_CANCELED, __func__);
  mDecodePromiseRequest.DisconnectIfExists();
  mDecodePromise.RejectIfExists(NS_ERROR_DOM_MEDIA_CANCELED, __func__);
  mDrainRequest.DisconnectIfExists();
  mFlushRequest.DisconnectIfExists();
  mFlushPromise.RejectIfExists(NS_ERROR_DOM_MEDIA_CANCELED, __func__);
  mShutdownRequest.DisconnectIfExists();

  if (mShutdownPromise) {
    // We have a shutdown in progress, return that promise instead as we can't
    // shutdown a decoder twice.
    RefPtr<ShutdownPromise> p = std::move(mShutdownPromise);
    return p;
  }
  return ShutdownDecoder();
}

RefPtr<ShutdownPromise> MediaChangeMonitor::ShutdownDecoder() {
  AssertOnThread();
  mConversionRequired.reset();
  if (mDecoder) {
    RefPtr<MediaDataDecoder> decoder = std::move(mDecoder);
    return decoder->Shutdown();
  }
  return ShutdownPromise::CreateAndResolve(true, __func__);
}

bool MediaChangeMonitor::IsHardwareAccelerated(
    nsACString& aFailureReason) const {
  if (mDecoder) {
    return mDecoder->IsHardwareAccelerated(aFailureReason);
  }
#ifdef MOZ_APPLEMEDIA
  // On mac, we can assume H264 is hardware accelerated for now.
  // This allows MediaCapabilities to report that playback will be smooth.
  // Which will always be.
  return true;
#else
  return MediaDataDecoder::IsHardwareAccelerated(aFailureReason);
#endif
}

void MediaChangeMonitor::SetSeekThreshold(const media::TimeUnit& aTime) {
  if (mDecoder) {
    mDecoder->SetSeekThreshold(aTime);
  } else {
    MediaDataDecoder::SetSeekThreshold(aTime);
  }
}

RefPtr<MediaChangeMonitor::CreateDecoderPromise>
MediaChangeMonitor::CreateDecoder() {
  MOZ_ASSERT(mThread && mThread->IsOnCurrentThread());

  mCurrentConfig = *mChangeMonitor->Config().GetAsVideoInfo();

  RefPtr<CreateDecoderPromise> p =
      mPDM->AsyncCreateDecoder({mCurrentConfig, mParams})
          ->Then(
              GetCurrentSerialEventTarget(), __func__,
              [self = RefPtr{this}, this](RefPtr<MediaDataDecoder>&& aDecoder) {
                mDecoder = std::move(aDecoder);
                DDLINKCHILD("decoder", mDecoder.get());
                return CreateDecoderPromise::CreateAndResolve(true, __func__);
              },
              [self = RefPtr{this}, this](const MediaResult& aError) {
                // We failed to create a decoder with the existing PDM; attempt
                // once again with a PDMFactory.
                RefPtr<PDMFactory> factory = new PDMFactory();
                RefPtr<CreateDecoderPromise> p =
                    factory
                        ->CreateDecoder({mCurrentConfig, mParams,
                                         CreateDecoderParams::NoWrapper(true)})
                        ->Then(
                            GetCurrentSerialEventTarget(), __func__,
                            [self, this](RefPtr<MediaDataDecoder>&& aDecoder) {
                              mDecoder = std::move(aDecoder);
                              DDLINKCHILD("decoder", mDecoder.get());
                              return CreateDecoderPromise::CreateAndResolve(
                                  true, __func__);
                            },
                            [self](const MediaResult& aError) {
                              return CreateDecoderPromise::CreateAndReject(
                                  aError, __func__);
                            });
                return p;
              });

  mDecoderInitialized = false;
  mNeedKeyframe = true;

  return p;
}

MediaResult MediaChangeMonitor::CreateDecoderAndInit(MediaRawData* aSample) {
  MediaResult rv = mChangeMonitor->CheckForChange(aSample);
  if (!NS_SUCCEEDED(rv) && rv != NS_ERROR_DOM_MEDIA_NEED_NEW_DECODER) {
    return rv;
  }

  if (!mChangeMonitor->CanBeInstantiated()) {
    // Nothing found yet, will try again later.
    return NS_ERROR_NOT_INITIALIZED;
  }

  CreateDecoder()
      ->Then(
          GetCurrentSerialEventTarget(), __func__,
          [self = RefPtr{this}, this, sample = RefPtr{aSample}] {
            mDecoderRequest.Complete();
            mDecoder->Init()
                ->Then(
                    GetCurrentSerialEventTarget(), __func__,
                    [self, sample, this](const TrackType aTrackType) {
                      mInitPromiseRequest.Complete();
                      mDecoderInitialized = true;
                      mConversionRequired = Some(mDecoder->NeedsConversion());
                      mCanRecycleDecoder = Some(CanRecycleDecoder());

                      if (!mFlushPromise.IsEmpty()) {
                        // A Flush is pending, abort the current operation.
                        mFlushPromise.Resolve(true, __func__);
                        return;
                      }

                      DecodeFirstSample(sample);
                    },
                    [self, this](const MediaResult& aError) {
                      mInitPromiseRequest.Complete();

                      if (!mFlushPromise.IsEmpty()) {
                        // A Flush is pending, abort the current operation.
                        mFlushPromise.Reject(aError, __func__);
                        return;
                      }

                      mDecodePromise.Reject(
                          MediaResult(
                              NS_ERROR_DOM_MEDIA_FATAL_ERR,
                              RESULT_DETAIL("Unable to initialize decoder")),
                          __func__);
                    })
                ->Track(mInitPromiseRequest);
          },
          [self = RefPtr{this}, this](const MediaResult& aError) {
            mDecoderRequest.Complete();
            if (!mFlushPromise.IsEmpty()) {
              // A Flush is pending, abort the current operation.
              mFlushPromise.Reject(aError, __func__);
              return;
            }
            mDecodePromise.Reject(
                MediaResult(NS_ERROR_DOM_MEDIA_FATAL_ERR,
                            RESULT_DETAIL("Unable to create decoder")),
                __func__);
          })
      ->Track(mDecoderRequest);
  return NS_ERROR_DOM_MEDIA_INITIALIZING_DECODER;
}

bool MediaChangeMonitor::CanRecycleDecoder() const {
  MOZ_ASSERT(mDecoder);
  return StaticPrefs::media_decoder_recycle_enabled() &&
         mDecoder->SupportDecoderRecycling();
}

void MediaChangeMonitor::DecodeFirstSample(MediaRawData* aSample) {
  // We feed all the data to AnnexB decoder as a non-keyframe could contain
  // the SPS/PPS when used with WebRTC and this data is needed by the decoder.
  if (mNeedKeyframe && !aSample->mKeyframe &&
      *mConversionRequired != ConversionRequired::kNeedAnnexB) {
    mDecodePromise.Resolve(std::move(mPendingFrames), __func__);
    mPendingFrames = DecodedData();
    return;
  }

  MediaResult rv = mChangeMonitor->PrepareSample(*mConversionRequired, aSample,
                                                 mNeedKeyframe);

  if (NS_FAILED(rv)) {
    mDecodePromise.Reject(rv, __func__);
    return;
  }

  if (aSample->mKeyframe) {
    mNeedKeyframe = false;
  }

  RefPtr<MediaChangeMonitor> self = this;
  mDecoder->Decode(aSample)
      ->Then(
          GetCurrentSerialEventTarget(), __func__,
          [self, this](MediaDataDecoder::DecodedData&& aResults) {
            mDecodePromiseRequest.Complete();
            mPendingFrames.AppendElements(std::move(aResults));
            mDecodePromise.Resolve(std::move(mPendingFrames), __func__);
            mPendingFrames = DecodedData();
          },
          [self, this](const MediaResult& aError) {
            mDecodePromiseRequest.Complete();
            mDecodePromise.Reject(aError, __func__);
          })
      ->Track(mDecodePromiseRequest);
}

MediaResult MediaChangeMonitor::CheckForChange(MediaRawData* aSample) {
  if (!mDecoder) {
    return CreateDecoderAndInit(aSample);
  }

  MediaResult rv = mChangeMonitor->CheckForChange(aSample);

  if (NS_SUCCEEDED(rv) || rv != NS_ERROR_DOM_MEDIA_NEED_NEW_DECODER) {
    return rv;
  }

  if (*mCanRecycleDecoder) {
    // Do not recreate the decoder, reuse it.
    mNeedKeyframe = true;
    return NS_OK;
  }

  // The content has changed, signal to drain the current decoder and once done
  // create a new one.
  DrainThenFlushDecoder(aSample);
  return NS_ERROR_DOM_MEDIA_INITIALIZING_DECODER;
}

void MediaChangeMonitor::DrainThenFlushDecoder(MediaRawData* aPendingSample) {
  AssertOnThread();
  MOZ_ASSERT(mDecoderInitialized);
  RefPtr<MediaRawData> sample = aPendingSample;
  RefPtr<MediaChangeMonitor> self = this;
  mDecoder->Drain()
      ->Then(
          GetCurrentSerialEventTarget(), __func__,
          [self, sample, this](MediaDataDecoder::DecodedData&& aResults) {
            mDrainRequest.Complete();
            if (!mFlushPromise.IsEmpty()) {
              // A Flush is pending, abort the current operation.
              mFlushPromise.Resolve(true, __func__);
              return;
            }
            if (aResults.Length() > 0) {
              mPendingFrames.AppendElements(std::move(aResults));
              DrainThenFlushDecoder(sample);
              return;
            }
            // We've completed the draining operation, we can now flush the
            // decoder.
            FlushThenShutdownDecoder(sample);
          },
          [self, this](const MediaResult& aError) {
            mDrainRequest.Complete();
            if (!mFlushPromise.IsEmpty()) {
              // A Flush is pending, abort the current operation.
              mFlushPromise.Reject(aError, __func__);
              return;
            }
            mDecodePromise.Reject(aError, __func__);
          })
      ->Track(mDrainRequest);
}

void MediaChangeMonitor::FlushThenShutdownDecoder(
    MediaRawData* aPendingSample) {
  AssertOnThread();
  MOZ_ASSERT(mDecoderInitialized);
  RefPtr<MediaRawData> sample = aPendingSample;
  RefPtr<MediaChangeMonitor> self = this;
  mDecoder->Flush()
      ->Then(
          GetCurrentSerialEventTarget(), __func__,
          [self, sample, this]() {
            mFlushRequest.Complete();

            if (!mFlushPromise.IsEmpty()) {
              // A Flush is pending, abort the current operation.
              mFlushPromise.Resolve(true, __func__);
              return;
            }

            mShutdownPromise = ShutdownDecoder();
            mShutdownPromise
                ->Then(
                    GetCurrentSerialEventTarget(), __func__,
                    [self, sample, this]() {
                      mShutdownRequest.Complete();
                      mShutdownPromise = nullptr;

                      if (!mFlushPromise.IsEmpty()) {
                        // A Flush is pending, abort the current
                        // operation.
                        mFlushPromise.Resolve(true, __func__);
                        return;
                      }

                      MediaResult rv = CreateDecoderAndInit(sample);
                      if (rv == NS_ERROR_DOM_MEDIA_INITIALIZING_DECODER) {
                        // All good so far, will continue later.
                        return;
                      }
                      MOZ_ASSERT(NS_FAILED(rv));
                      mDecodePromise.Reject(rv, __func__);
                      return;
                    },
                    [] { MOZ_CRASH("Can't reach here'"); })
                ->Track(mShutdownRequest);
          },
          [self, this](const MediaResult& aError) {
            mFlushRequest.Complete();
            if (!mFlushPromise.IsEmpty()) {
              // A Flush is pending, abort the current operation.
              mFlushPromise.Reject(aError, __func__);
              return;
            }
            mDecodePromise.Reject(aError, __func__);
          })
      ->Track(mFlushRequest);
}

}  // namespace mozilla