gecko-dev/dom/media/ADTSDemuxer.cpp

/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
/* vim: set ts=8 sts=2 et sw=2 tw=80: */
/* 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 "ADTSDemuxer.h"

#include "TimeUnits.h"
#include "VideoUtils.h"
#include "mozilla/UniquePtr.h"
#include <inttypes.h>

extern mozilla::LazyLogModule gMediaDemuxerLog;
#define ADTSLOG(msg, ...) \
  DDMOZ_LOG(gMediaDemuxerLog, LogLevel::Debug, msg, ##__VA_ARGS__)
#define ADTSLOGV(msg, ...) \
  DDMOZ_LOG(gMediaDemuxerLog, LogLevel::Verbose, msg, ##__VA_ARGS__)

namespace mozilla {
namespace adts {

// adts::FrameHeader - Holds the ADTS frame header and its parsing
// state.
//
// ADTS Frame Structure
//
// 11111111 1111BCCD EEFFFFGH HHIJKLMM MMMMMMMM MMMOOOOO OOOOOOPP(QQQQQQQQ
// QQQQQQQQ)
//
// Header consists of 7 or 9 bytes(without or with CRC).
// Letter   Length(bits)  Description
// { sync } 12            syncword 0xFFF, all bits must be 1
// B        1             MPEG Version: 0 for MPEG-4, 1 for MPEG-2
// C        2             Layer: always 0
// D        1             protection absent, Warning, set to 1 if there is no
//                        CRC and 0 if there is CRC
// E        2             profile, the MPEG-4 Audio Object Type minus 1
// F        4             MPEG-4 Sampling Frequency Index (15 is forbidden)
// H        3             MPEG-4 Channel Configuration (in the case of 0, the
//                        channel configuration is sent via an in-band PCE)
// M        13            frame length, this value must include 7 or 9 bytes of
//                        header length: FrameLength =
//                          (ProtectionAbsent == 1 ? 7 : 9) + size(AACFrame)
// O        11            Buffer fullness
// P        2             Number of AAC frames(RDBs) in ADTS frame minus 1, for
//                        maximum compatibility always use 1 AAC frame per ADTS
//                        frame
// Q        16            CRC if protection absent is 0
class FrameHeader {
 public:
  uint32_t mFrameLength;
  uint32_t mSampleRate;
  uint32_t mSamples;
  uint32_t mChannels;
  uint8_t mObjectType;
  uint8_t mSamplingIndex;
  uint8_t mChannelConfig;
  uint8_t mNumAACFrames;
  bool mHaveCrc;

  // Returns whether aPtr matches a valid ADTS header sync marker
  static bool MatchesSync(const uint8_t* aPtr) {
    return aPtr[0] == 0xFF && (aPtr[1] & 0xF6) == 0xF0;
  }

  FrameHeader() { Reset(); }

  // Header size
  uint64_t HeaderSize() const { return (mHaveCrc) ? 9 : 7; }

  bool IsValid() const { return mFrameLength > 0; }

  // Resets the state to allow for a new parsing session.
  void Reset() { PodZero(this); }

  // Returns whether the byte creates a valid sequence up to this point.
  bool Parse(const uint8_t* aPtr) {
    const uint8_t* p = aPtr;

    if (!MatchesSync(p)) {
      return false;
    }

    // AAC has 1024 samples per frame per channel.
    mSamples = 1024;

    mHaveCrc = !(p[1] & 0x01);
    mObjectType = ((p[2] & 0xC0) >> 6) + 1;
    mSamplingIndex = (p[2] & 0x3C) >> 2;
    mChannelConfig = (p[2] & 0x01) << 2 | (p[3] & 0xC0) >> 6;
    mFrameLength = static_cast<uint32_t>(
        (p[3] & 0x03) << 11 | (p[4] & 0xFF) << 3 | (p[5] & 0xE0) >> 5);
    mNumAACFrames = (p[6] & 0x03) + 1;

    static const uint32_t SAMPLE_RATES[16] = {96000, 88200, 64000, 48000, 44100,
                                              32000, 24000, 22050, 16000, 12000,
                                              11025, 8000,  7350};
    mSampleRate = SAMPLE_RATES[mSamplingIndex];

    MOZ_ASSERT(mChannelConfig < 8);
    mChannels = (mChannelConfig == 7) ? 8 : mChannelConfig;

    return true;
  }
};

// adts::Frame - Frame meta container used to parse and hold a frame
// header and side info.
class Frame {
 public:
  Frame() : mOffset(0), mHeader() {}

  uint64_t Offset() const { return mOffset; }
  size_t Length() const {
    // TODO: If fields are zero'd when invalid, this check wouldn't be
    // necessary.
    if (!mHeader.IsValid()) {
      return 0;
    }

    return mHeader.mFrameLength;
  }

  // Returns the offset to the start of frame's raw data.
  uint64_t PayloadOffset() const { return mOffset + mHeader.HeaderSize(); }

  // Returns the length of the frame's raw data (excluding the header) in bytes.
  size_t PayloadLength() const {
    // TODO: If fields are zero'd when invalid, this check wouldn't be
    // necessary.
    if (!mHeader.IsValid()) {
      return 0;
    }

    return mHeader.mFrameLength - mHeader.HeaderSize();
  }

  // Returns the parsed frame header.
  const FrameHeader& Header() const { return mHeader; }

  bool IsValid() const { return mHeader.IsValid(); }

  // Resets the frame header and data.
  void Reset() {
    mHeader.Reset();
    mOffset = 0;
  }

  // Returns whether the valid
  bool Parse(uint64_t aOffset, const uint8_t* aStart, const uint8_t* aEnd) {
    MOZ_ASSERT(aStart && aEnd);

    bool found = false;
    const uint8_t* ptr = aStart;
    // Require at least 7 bytes of data at the end of the buffer for the minimum
    // ADTS frame header.
    while (ptr < aEnd - 7 && !found) {
      found = mHeader.Parse(ptr);
      ptr++;
    }

    mOffset = aOffset + (static_cast<size_t>(ptr - aStart)) - 1u;

    return found;
  }

 private:
  // The offset to the start of the header.
  uint64_t mOffset;

  // The currently parsed frame header.
  FrameHeader mHeader;
};

class FrameParser {
 public:
  // Returns the currently parsed frame. Reset via Reset or EndFrameSession.
  const Frame& CurrentFrame() const { return mFrame; }

  // Returns the first parsed frame. Reset via Reset.
  const Frame& FirstFrame() const { return mFirstFrame; }

  // Resets the parser. Don't use between frames as first frame data is reset.
  void Reset() {
    EndFrameSession();
    mFirstFrame.Reset();
  }

  // Clear the last parsed frame to allow for next frame parsing, i.e.:
  // - sets PrevFrame to CurrentFrame
  // - resets the CurrentFrame
  // - resets ID3Header if no valid header was parsed yet
  void EndFrameSession() { mFrame.Reset(); }

  // Parses contents of given ByteReader for a valid frame header and returns
  // true if one was found. After returning, the variable passed to
  // 'aBytesToSkip' holds the amount of bytes to be skipped (if any) in order to
  // jump across a large ID3v2 tag spanning multiple buffers.
  bool Parse(uint64_t aOffset, const uint8_t* aStart, const uint8_t* aEnd) {
    const bool found = mFrame.Parse(aOffset, aStart, aEnd);

    if (mFrame.Length() && !mFirstFrame.Length()) {
      mFirstFrame = mFrame;
    }

    return found;
  }

 private:
  // We keep the first parsed frame around for static info access, the
  // previously parsed frame for debugging and the currently parsed frame.
  Frame mFirstFrame;
  Frame mFrame;
};

// Initialize the AAC AudioSpecificConfig.
// Only handles two-byte version for AAC-LC.
static void InitAudioSpecificConfig(const Frame& frame,
                                    MediaByteBuffer* aBuffer) {
  const FrameHeader& header = frame.Header();
  MOZ_ASSERT(header.IsValid());

  int audioObjectType = header.mObjectType;
  int samplingFrequencyIndex = header.mSamplingIndex;
  int channelConfig = header.mChannelConfig;

  uint8_t asc[2];
  asc[0] = (audioObjectType & 0x1F) << 3 | (samplingFrequencyIndex & 0x0E) >> 1;
  asc[1] = (samplingFrequencyIndex & 0x01) << 7 | (channelConfig & 0x0F) << 3;

  aBuffer->AppendElements(asc, 2);
}

}  // namespace adts

using media::TimeUnit;

// ADTSDemuxer

ADTSDemuxer::ADTSDemuxer(MediaResource* aSource) : mSource(aSource) {
  DDLINKCHILD("source", aSource);
}

bool ADTSDemuxer::InitInternal() {
  if (!mTrackDemuxer) {
    mTrackDemuxer = new ADTSTrackDemuxer(mSource);
    DDLINKCHILD("track demuxer", mTrackDemuxer.get());
  }
  return mTrackDemuxer->Init();
}

RefPtr<ADTSDemuxer::InitPromise> ADTSDemuxer::Init() {
  if (!InitInternal()) {
    ADTSLOG("Init() failure: waiting for data");

    return InitPromise::CreateAndReject(NS_ERROR_DOM_MEDIA_METADATA_ERR,
                                        __func__);
  }

  ADTSLOG("Init() successful");
  return InitPromise::CreateAndResolve(NS_OK, __func__);
}

uint32_t ADTSDemuxer::GetNumberTracks(TrackInfo::TrackType aType) const {
  return (aType == TrackInfo::kAudioTrack) ? 1 : 0;
}

already_AddRefed<MediaTrackDemuxer> ADTSDemuxer::GetTrackDemuxer(
    TrackInfo::TrackType aType, uint32_t aTrackNumber) {
  if (!mTrackDemuxer) {
    return nullptr;
  }

  return RefPtr<ADTSTrackDemuxer>(mTrackDemuxer).forget();
}

bool ADTSDemuxer::IsSeekable() const {
  int64_t length = mSource->GetLength();
  if (length > -1) return true;
  return false;
}

// ADTSTrackDemuxer
ADTSTrackDemuxer::ADTSTrackDemuxer(MediaResource* aSource)
    : mSource(aSource),
      mParser(new adts::FrameParser()),
      mOffset(0),
      mNumParsedFrames(0),
      mFrameIndex(0),
      mTotalFrameLen(0),
      mSamplesPerFrame(0),
      mSamplesPerSecond(0),
      mChannels(0) {
  DDLINKCHILD("source", aSource);
  Reset();
}

ADTSTrackDemuxer::~ADTSTrackDemuxer() { delete mParser; }

bool ADTSTrackDemuxer::Init() {
  FastSeek(TimeUnit::Zero());
  // Read the first frame to fetch sample rate and other meta data.
  RefPtr<MediaRawData> frame(GetNextFrame(FindNextFrame(true)));

  ADTSLOG("Init StreamLength()=%" PRId64 " first-frame-found=%d",
          StreamLength(), !!frame);

  if (!frame) {
    return false;
  }

  // Rewind back to the stream begin to avoid dropping the first frame.
  FastSeek(TimeUnit::Zero());

  if (!mSamplesPerSecond) {
    return false;
  }

  if (!mInfo) {
    mInfo = MakeUnique<AudioInfo>();
  }

  mInfo->mRate = mSamplesPerSecond;
  mInfo->mChannels = mChannels;
  mInfo->mBitDepth = 16;
  mInfo->mDuration = Duration();

  // AAC Specific information
  mInfo->mMimeType = "audio/mp4a-latm";

  // Configure AAC codec-specific values.
  // For AAC, mProfile and mExtendedProfile contain the audioObjectType from
  // Table 1.3 -- Audio Profile definition, ISO/IEC 14496-3. Eg. 2 == AAC LC
  mInfo->mProfile = mInfo->mExtendedProfile =
      mParser->FirstFrame().Header().mObjectType;
  AudioCodecSpecificBinaryBlob blob;
  InitAudioSpecificConfig(mParser->FirstFrame(), blob.mBinaryBlob);
  mInfo->mCodecSpecificConfig = AudioCodecSpecificVariant{std::move(blob)};

  ADTSLOG("Init mInfo={mRate=%u mChannels=%u mBitDepth=%u mDuration=%" PRId64
          "}",
          mInfo->mRate, mInfo->mChannels, mInfo->mBitDepth,
          mInfo->mDuration.ToMicroseconds());

  // AAC encoder delay is by default 2112 audio frames.
  // See
  // https://developer.apple.com/library/content/documentation/QuickTime/QTFF/QTFFAppenG/QTFFAppenG.html
  // So we always seek 2112 frames prior the seeking point.
  mPreRoll = TimeUnit::FromMicroseconds(2112 * 1000000ULL / mSamplesPerSecond);
  return mChannels;
}

UniquePtr<TrackInfo> ADTSTrackDemuxer::GetInfo() const {
  return mInfo->Clone();
}

RefPtr<ADTSTrackDemuxer::SeekPromise> ADTSTrackDemuxer::Seek(
    const TimeUnit& aTime) {
  // Efficiently seek to the position.
  const TimeUnit time = aTime > mPreRoll ? aTime - mPreRoll : TimeUnit::Zero();
  FastSeek(time);
  // Correct seek position by scanning the next frames.
  const TimeUnit seekTime = ScanUntil(time);

  return SeekPromise::CreateAndResolve(seekTime, __func__);
}

TimeUnit ADTSTrackDemuxer::FastSeek(const TimeUnit& aTime) {
  ADTSLOG("FastSeek(%" PRId64 ") avgFrameLen=%f mNumParsedFrames=%" PRIu64
          " mFrameIndex=%" PRId64 " mOffset=%" PRIu64,
          aTime.ToMicroseconds(), AverageFrameLength(), mNumParsedFrames,
          mFrameIndex, mOffset);

  const uint64_t firstFrameOffset = mParser->FirstFrame().Offset();
  if (!aTime.ToMicroseconds()) {
    // Quick seek to the beginning of the stream.
    mOffset = firstFrameOffset;
  } else if (AverageFrameLength() > 0) {
    mOffset =
        firstFrameOffset + FrameIndexFromTime(aTime) * AverageFrameLength();
  }

  const int64_t streamLength = StreamLength();
  if (mOffset > firstFrameOffset && streamLength > 0) {
    mOffset = std::min(static_cast<uint64_t>(streamLength - 1), mOffset);
  }

  mFrameIndex = FrameIndexFromOffset(mOffset);
  mParser->EndFrameSession();

  ADTSLOG("FastSeek End avgFrameLen=%f mNumParsedFrames=%" PRIu64
          " mFrameIndex=%" PRId64 " mFirstFrameOffset=%" PRIu64
          " mOffset=%" PRIu64 " SL=%" PRIu64 "",
          AverageFrameLength(), mNumParsedFrames, mFrameIndex, firstFrameOffset,
          mOffset, streamLength);

  return Duration(mFrameIndex);
}

TimeUnit ADTSTrackDemuxer::ScanUntil(const TimeUnit& aTime) {
  ADTSLOG("ScanUntil(%" PRId64 ") avgFrameLen=%f mNumParsedFrames=%" PRIu64
          " mFrameIndex=%" PRId64 " mOffset=%" PRIu64,
          aTime.ToMicroseconds(), AverageFrameLength(), mNumParsedFrames,
          mFrameIndex, mOffset);

  if (!aTime.ToMicroseconds()) {
    return FastSeek(aTime);
  }

  if (Duration(mFrameIndex) > aTime) {
    FastSeek(aTime);
  }

  while (SkipNextFrame(FindNextFrame()) && Duration(mFrameIndex + 1) < aTime) {
    ADTSLOGV("ScanUntil* avgFrameLen=%f mNumParsedFrames=%" PRIu64
             " mFrameIndex=%" PRId64 " mOffset=%" PRIu64 " Duration=%" PRId64,
             AverageFrameLength(), mNumParsedFrames, mFrameIndex, mOffset,
             Duration(mFrameIndex + 1).ToMicroseconds());
  }

  ADTSLOG("ScanUntil End avgFrameLen=%f mNumParsedFrames=%" PRIu64
          " mFrameIndex=%" PRId64 " mOffset=%" PRIu64,
          AverageFrameLength(), mNumParsedFrames, mFrameIndex, mOffset);

  return Duration(mFrameIndex);
}

RefPtr<ADTSTrackDemuxer::SamplesPromise> ADTSTrackDemuxer::GetSamples(
    int32_t aNumSamples) {
  ADTSLOGV("GetSamples(%d) Begin mOffset=%" PRIu64 " mNumParsedFrames=%" PRIu64
           " mFrameIndex=%" PRId64 " mTotalFrameLen=%" PRIu64
           " mSamplesPerFrame=%d "
           "mSamplesPerSecond=%d mChannels=%d",
           aNumSamples, mOffset, mNumParsedFrames, mFrameIndex, mTotalFrameLen,
           mSamplesPerFrame, mSamplesPerSecond, mChannels);

  MOZ_ASSERT(aNumSamples);

  RefPtr<SamplesHolder> frames = new SamplesHolder();

  while (aNumSamples--) {
    RefPtr<MediaRawData> frame(GetNextFrame(FindNextFrame()));
    if (!frame) break;
    frames->AppendSample(frame);
  }

  ADTSLOGV(
      "GetSamples() End mSamples.Size()=%zu aNumSamples=%d mOffset=%" PRIu64
      " mNumParsedFrames=%" PRIu64 " mFrameIndex=%" PRId64
      " mTotalFrameLen=%" PRIu64
      " mSamplesPerFrame=%d mSamplesPerSecond=%d "
      "mChannels=%d",
      frames->GetSamples().Length(), aNumSamples, mOffset, mNumParsedFrames,
      mFrameIndex, mTotalFrameLen, mSamplesPerFrame, mSamplesPerSecond,
      mChannels);

  if (frames->GetSamples().IsEmpty()) {
    return SamplesPromise::CreateAndReject(NS_ERROR_DOM_MEDIA_END_OF_STREAM,
                                           __func__);
  }

  return SamplesPromise::CreateAndResolve(frames, __func__);
}

void ADTSTrackDemuxer::Reset() {
  ADTSLOG("Reset()");
  MOZ_ASSERT(mParser);
  if (mParser) {
    mParser->Reset();
  }
  FastSeek(TimeUnit::Zero());
}

RefPtr<ADTSTrackDemuxer::SkipAccessPointPromise>
ADTSTrackDemuxer::SkipToNextRandomAccessPoint(const TimeUnit& aTimeThreshold) {
  // Will not be called for audio-only resources.
  return SkipAccessPointPromise::CreateAndReject(
      SkipFailureHolder(NS_ERROR_DOM_MEDIA_DEMUXER_ERR, 0), __func__);
}

int64_t ADTSTrackDemuxer::GetResourceOffset() const { return mOffset; }

media::TimeIntervals ADTSTrackDemuxer::GetBuffered() {
  auto duration = Duration();

  if (!duration.IsPositive()) {
    return media::TimeIntervals();
  }

  AutoPinned<MediaResource> stream(mSource.GetResource());
  return GetEstimatedBufferedTimeRanges(stream, duration.ToMicroseconds());
}

int64_t ADTSTrackDemuxer::StreamLength() const { return mSource.GetLength(); }

TimeUnit ADTSTrackDemuxer::Duration() const {
  if (!mNumParsedFrames) {
    return TimeUnit::FromMicroseconds(-1);
  }

  const int64_t streamLen = StreamLength();
  if (streamLen < 0) {
    // Unknown length, we can't estimate duration.
    return TimeUnit::FromMicroseconds(-1);
  }
  const int64_t firstFrameOffset = mParser->FirstFrame().Offset();
  int64_t numFrames = (streamLen - firstFrameOffset) / AverageFrameLength();
  return Duration(numFrames);
}

TimeUnit ADTSTrackDemuxer::Duration(int64_t aNumFrames) const {
  if (!mSamplesPerSecond) {
    return TimeUnit::FromMicroseconds(-1);
  }

  return FramesToTimeUnit(aNumFrames * mSamplesPerFrame, mSamplesPerSecond);
}

const adts::Frame& ADTSTrackDemuxer::FindNextFrame(
    bool findFirstFrame /*= false*/) {
  static const int BUFFER_SIZE = 4096;
  static const int MAX_SKIPPED_BYTES = 10 * BUFFER_SIZE;

  ADTSLOGV("FindNext() Begin mOffset=%" PRIu64 " mNumParsedFrames=%" PRIu64
           " mFrameIndex=%" PRId64 " mTotalFrameLen=%" PRIu64
           " mSamplesPerFrame=%d mSamplesPerSecond=%d mChannels=%d",
           mOffset, mNumParsedFrames, mFrameIndex, mTotalFrameLen,
           mSamplesPerFrame, mSamplesPerSecond, mChannels);

  uint8_t buffer[BUFFER_SIZE];
  uint32_t read = 0;

  bool foundFrame = false;
  uint64_t frameHeaderOffset = mOffset;

  // Prepare the parser for the next frame parsing session.
  mParser->EndFrameSession();

  // Check whether we've found a valid ADTS frame.
  while (!foundFrame) {
    if ((read = Read(buffer, frameHeaderOffset, BUFFER_SIZE)) == 0) {
      ADTSLOG("FindNext() EOS without a frame");
      break;
    }

    if (frameHeaderOffset - mOffset > MAX_SKIPPED_BYTES) {
      ADTSLOG("FindNext() exceeded MAX_SKIPPED_BYTES without a frame");
      break;
    }

    const adts::Frame& currentFrame = mParser->CurrentFrame();
    foundFrame = mParser->Parse(frameHeaderOffset, buffer, buffer + read);
    if (findFirstFrame && foundFrame) {
      // Check for sync marker after the found frame, since it's
      // possible to find sync marker in AAC data. If sync marker
      // exists after the current frame then we've found a frame
      // header.
      uint64_t nextFrameHeaderOffset =
          currentFrame.Offset() + currentFrame.Length();
      uint32_t read = Read(buffer, nextFrameHeaderOffset, 2);
      if (read != 2 || !adts::FrameHeader::MatchesSync(buffer)) {
        frameHeaderOffset = currentFrame.Offset() + 1;
        mParser->Reset();
        foundFrame = false;
        continue;
      }
    }

    if (foundFrame) {
      break;
    }

    // Minimum header size is 7 bytes.
    uint64_t advance = read - 7;

    // Check for offset overflow.
    if (frameHeaderOffset + advance <= frameHeaderOffset) {
      break;
    }

    frameHeaderOffset += advance;
  }

  if (!foundFrame || !mParser->CurrentFrame().Length()) {
    ADTSLOG(
        "FindNext() Exit foundFrame=%d mParser->CurrentFrame().Length()=%zu ",
        foundFrame, mParser->CurrentFrame().Length());
    mParser->Reset();
    return mParser->CurrentFrame();
  }

  ADTSLOGV("FindNext() End mOffset=%" PRIu64 " mNumParsedFrames=%" PRIu64
           " mFrameIndex=%" PRId64 " frameHeaderOffset=%" PRId64
           " mTotalFrameLen=%" PRIu64
           " mSamplesPerFrame=%d mSamplesPerSecond=%d"
           " mChannels=%d",
           mOffset, mNumParsedFrames, mFrameIndex, frameHeaderOffset,
           mTotalFrameLen, mSamplesPerFrame, mSamplesPerSecond, mChannels);

  return mParser->CurrentFrame();
}

bool ADTSTrackDemuxer::SkipNextFrame(const adts::Frame& aFrame) {
  if (!mNumParsedFrames || !aFrame.Length()) {
    RefPtr<MediaRawData> frame(GetNextFrame(aFrame));
    return frame;
  }

  UpdateState(aFrame);

  ADTSLOGV("SkipNext() End mOffset=%" PRIu64 " mNumParsedFrames=%" PRIu64
           " mFrameIndex=%" PRId64 " mTotalFrameLen=%" PRIu64
           " mSamplesPerFrame=%d mSamplesPerSecond=%d mChannels=%d",
           mOffset, mNumParsedFrames, mFrameIndex, mTotalFrameLen,
           mSamplesPerFrame, mSamplesPerSecond, mChannels);

  return true;
}

already_AddRefed<MediaRawData> ADTSTrackDemuxer::GetNextFrame(
    const adts::Frame& aFrame) {
  ADTSLOG("GetNext() Begin({mOffset=%" PRIu64 " HeaderSize()=%" PRIu64
          " Length()=%zu})",
          aFrame.Offset(), aFrame.Header().HeaderSize(),
          aFrame.PayloadLength());
  if (!aFrame.IsValid()) return nullptr;

  const int64_t offset = aFrame.PayloadOffset();
  const uint32_t length = aFrame.PayloadLength();

  RefPtr<MediaRawData> frame = new MediaRawData();
  frame->mOffset = offset;

  UniquePtr<MediaRawDataWriter> frameWriter(frame->CreateWriter());
  if (!frameWriter->SetSize(length)) {
    ADTSLOG("GetNext() Exit failed to allocated media buffer");
    return nullptr;
  }

  const uint32_t read = Read(frameWriter->Data(), offset, length);
  if (read != length) {
    ADTSLOG("GetNext() Exit read=%u frame->Size()=%zu", read, frame->Size());
    return nullptr;
  }

  UpdateState(aFrame);

  frame->mTime = Duration(mFrameIndex - 1);
  frame->mDuration = Duration(1);
  frame->mTimecode = frame->mTime;
  frame->mKeyframe = true;

  MOZ_ASSERT(!frame->mTime.IsNegative());
  MOZ_ASSERT(frame->mDuration.IsPositive());

  ADTSLOGV("GetNext() End mOffset=%" PRIu64 " mNumParsedFrames=%" PRIu64
           " mFrameIndex=%" PRId64 " mTotalFrameLen=%" PRIu64
           " mSamplesPerFrame=%d mSamplesPerSecond=%d mChannels=%d",
           mOffset, mNumParsedFrames, mFrameIndex, mTotalFrameLen,
           mSamplesPerFrame, mSamplesPerSecond, mChannels);

  return frame.forget();
}

int64_t ADTSTrackDemuxer::FrameIndexFromOffset(uint64_t aOffset) const {
  uint64_t frameIndex = 0;

  if (AverageFrameLength() > 0) {
    frameIndex =
        (aOffset - mParser->FirstFrame().Offset()) / AverageFrameLength();
  }

  ADTSLOGV("FrameIndexFromOffset(%" PRId64 ") -> %" PRId64, aOffset,
           frameIndex);
  return frameIndex;
}

int64_t ADTSTrackDemuxer::FrameIndexFromTime(const TimeUnit& aTime) const {
  int64_t frameIndex = 0;
  if (mSamplesPerSecond > 0 && mSamplesPerFrame > 0) {
    frameIndex = aTime.ToSeconds() * mSamplesPerSecond / mSamplesPerFrame - 1;
  }

  ADTSLOGV("FrameIndexFromOffset(%fs) -> %" PRId64, aTime.ToSeconds(),
           frameIndex);
  return std::max<int64_t>(0, frameIndex);
}

void ADTSTrackDemuxer::UpdateState(const adts::Frame& aFrame) {
  uint32_t frameLength = aFrame.Length();
  // Prevent overflow.
  if (mTotalFrameLen + frameLength < mTotalFrameLen) {
    // These variables have a linear dependency and are only used to derive the
    // average frame length.
    mTotalFrameLen /= 2;
    mNumParsedFrames /= 2;
  }

  // Full frame parsed, move offset to its end.
  mOffset = aFrame.Offset() + frameLength;
  mTotalFrameLen += frameLength;

  if (!mSamplesPerFrame) {
    const adts::FrameHeader& header = aFrame.Header();
    mSamplesPerFrame = header.mSamples;
    mSamplesPerSecond = header.mSampleRate;
    mChannels = header.mChannels;
  }

  ++mNumParsedFrames;
  ++mFrameIndex;
  MOZ_ASSERT(mFrameIndex > 0);
}

uint32_t ADTSTrackDemuxer::Read(uint8_t* aBuffer, int64_t aOffset,
                                int32_t aSize) {
  ADTSLOGV("ADTSTrackDemuxer::Read(%p %" PRId64 " %d)", aBuffer, aOffset,
           aSize);

  const int64_t streamLen = StreamLength();
  if (mInfo && streamLen > 0) {
    int64_t max = streamLen > aOffset ? streamLen - aOffset : 0;
    // Prevent blocking reads after successful initialization.
    aSize = std::min<int64_t>(aSize, max);
  }

  uint32_t read = 0;
  ADTSLOGV("ADTSTrackDemuxer::Read        -> ReadAt(%d)", aSize);
  const nsresult rv = mSource.ReadAt(aOffset, reinterpret_cast<char*>(aBuffer),
                                     static_cast<uint32_t>(aSize), &read);
  NS_ENSURE_SUCCESS(rv, 0);
  return read;
}

double ADTSTrackDemuxer::AverageFrameLength() const {
  if (mNumParsedFrames) {
    return static_cast<double>(mTotalFrameLen) / mNumParsedFrames;
  }

  return 0.0;
}

/* static */
bool ADTSDemuxer::ADTSSniffer(const uint8_t* aData, const uint32_t aLength) {
  if (aLength < 7) {
    return false;
  }
  if (!adts::FrameHeader::MatchesSync(aData)) {
    return false;
  }
  auto parser = MakeUnique<adts::FrameParser>();

  if (!parser->Parse(0, aData, aData + aLength)) {
    return false;
  }
  const adts::Frame& currentFrame = parser->CurrentFrame();
  // Check for sync marker after the found frame, since it's
  // possible to find sync marker in AAC data. If sync marker
  // exists after the current frame then we've found a frame
  // header.
  uint64_t nextFrameHeaderOffset =
      currentFrame.Offset() + currentFrame.Length();
  MOZ_ASSERT(aLength >= nextFrameHeaderOffset);
  return aLength > nextFrameHeaderOffset &&
         aLength - nextFrameHeaderOffset >= 2 &&
         adts::FrameHeader::MatchesSync(aData + nextFrameHeaderOffset);
}

}  // namespace mozilla