Move the MP3 code to it's own directory

1 files changed, 1340 insertions, 0 deletions

diff --git a/dom/media/mp3/MP3Demuxer.cpp b/dom/media/mp3/MP3Demuxer.cpp
new file mode 100644
index 000000000..5a98cabfe
--- /dev/null
+++ b/dom/media/mp3/MP3Demuxer.cpp
@@ -0,0 +1,1340 @@
+/* -*- 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 "MP3Demuxer.h"
+
+#include <inttypes.h>
+#include <algorithm>
+
+#include "mozilla/Assertions.h"
+#include "mozilla/EndianUtils.h"
+#include "nsAutoPtr.h"
+#include "VideoUtils.h"
+#include "TimeUnits.h"
+#include "prenv.h"
+
+#ifdef PR_LOGGING
+extern mozilla::LazyLogModule gMediaDemuxerLog;
+#define MP3LOG(msg, ...) \
+  MOZ_LOG(gMediaDemuxerLog, LogLevel::Debug, ("MP3Demuxer " msg, ##__VA_ARGS__))
+#define MP3LOGV(msg, ...) \
+  MOZ_LOG(gMediaDemuxerLog, LogLevel::Verbose, ("MP3Demuxer " msg, ##__VA_ARGS__))
+#else
+#define MP3LOG(msg, ...)
+#define MP3LOGV(msg, ...)
+#endif
+
+using mozilla::media::TimeUnit;
+using mozilla::media::TimeInterval;
+using mozilla::media::TimeIntervals;
+using mp4_demuxer::ByteReader;
+
+namespace mozilla {
+
+// MP3Demuxer
+
+MP3Demuxer::MP3Demuxer(MediaResource* aSource)
+  : mSource(aSource)
+{}
+
+bool
+MP3Demuxer::InitInternal() {
+  if (!mTrackDemuxer) {
+    mTrackDemuxer = new MP3TrackDemuxer(mSource);
+  }
+  return mTrackDemuxer->Init();
+}
+
+RefPtr<MP3Demuxer::InitPromise>
+MP3Demuxer::Init() {
+  if (!InitInternal()) {
+    MP3LOG("MP3Demuxer::Init() failure: waiting for data");
+
+    return InitPromise::CreateAndReject(
+      NS_ERROR_DOM_MEDIA_METADATA_ERR, __func__);
+  }
+
+  MP3LOG("MP3Demuxer::Init() successful");
+  return InitPromise::CreateAndResolve(NS_OK, __func__);
+}
+
+bool
+MP3Demuxer::HasTrackType(TrackInfo::TrackType aType) const {
+  return aType == TrackInfo::kAudioTrack;
+}
+
+uint32_t
+MP3Demuxer::GetNumberTracks(TrackInfo::TrackType aType) const {
+  return aType == TrackInfo::kAudioTrack ? 1u : 0u;
+}
+
+already_AddRefed<MediaTrackDemuxer>
+MP3Demuxer::GetTrackDemuxer(TrackInfo::TrackType aType, uint32_t aTrackNumber) {
+  if (!mTrackDemuxer) {
+    return nullptr;
+  }
+  return RefPtr<MP3TrackDemuxer>(mTrackDemuxer).forget();
+}
+
+bool
+MP3Demuxer::IsSeekable() const {
+  return true;
+}
+
+void
+MP3Demuxer::NotifyDataArrived() {
+  // TODO: bug 1169485.
+  NS_WARNING("Unimplemented function NotifyDataArrived");
+  MP3LOGV("NotifyDataArrived()");
+}
+
+void
+MP3Demuxer::NotifyDataRemoved() {
+  // TODO: bug 1169485.
+  NS_WARNING("Unimplemented function NotifyDataRemoved");
+  MP3LOGV("NotifyDataRemoved()");
+}
+
+
+// MP3TrackDemuxer
+
+MP3TrackDemuxer::MP3TrackDemuxer(MediaResource* aSource)
+  : mSource(aSource)
+  , mOffset(0)
+  , mFirstFrameOffset(0)
+  , mNumParsedFrames(0)
+  , mFrameIndex(0)
+  , mTotalFrameLen(0)
+  , mSamplesPerFrame(0)
+  , mSamplesPerSecond(0)
+  , mChannels(0)
+{
+  Reset();
+}
+
+bool
+MP3TrackDemuxer::Init() {
+  Reset();
+  FastSeek(TimeUnit());
+  // Read the first frame to fetch sample rate and other meta data.
+  RefPtr<MediaRawData> frame(GetNextFrame(FindFirstFrame()));
+
+  MP3LOG("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());
+
+  if (!mInfo) {
+    mInfo = MakeUnique<AudioInfo>();
+  }
+
+  mInfo->mRate = mSamplesPerSecond;
+  mInfo->mChannels = mChannels;
+  mInfo->mBitDepth = 16;
+  mInfo->mMimeType = "audio/mpeg";
+  mInfo->mDuration = Duration().ToMicroseconds();
+
+  MP3LOG("Init mInfo={mRate=%d mChannels=%d mBitDepth=%d mDuration=%" PRId64 "}",
+         mInfo->mRate, mInfo->mChannels, mInfo->mBitDepth,
+         mInfo->mDuration);
+
+  return mSamplesPerSecond && mChannels;
+}
+
+media::TimeUnit
+MP3TrackDemuxer::SeekPosition() const {
+  TimeUnit pos = Duration(mFrameIndex);
+  if (Duration() > TimeUnit()) {
+    pos = std::min(Duration(), pos);
+  }
+  return pos;
+}
+
+const FrameParser::Frame&
+MP3TrackDemuxer::LastFrame() const {
+  return mParser.PrevFrame();
+}
+
+RefPtr<MediaRawData>
+MP3TrackDemuxer::DemuxSample() {
+  return GetNextFrame(FindNextFrame());
+}
+
+const ID3Parser::ID3Header&
+MP3TrackDemuxer::ID3Header() const {
+  return mParser.ID3Header();
+}
+
+const FrameParser::VBRHeader&
+MP3TrackDemuxer::VBRInfo() const {
+  return mParser.VBRInfo();
+}
+
+UniquePtr<TrackInfo>
+MP3TrackDemuxer::GetInfo() const {
+  return mInfo->Clone();
+}
+
+RefPtr<MP3TrackDemuxer::SeekPromise>
+MP3TrackDemuxer::Seek(TimeUnit aTime) {
+  // Efficiently seek to the position.
+  FastSeek(aTime);
+  // Correct seek position by scanning the next frames.
+  const TimeUnit seekTime = ScanUntil(aTime);
+
+  return SeekPromise::CreateAndResolve(seekTime, __func__);
+}
+
+TimeUnit
+MP3TrackDemuxer::FastSeek(const TimeUnit& aTime) {
+  MP3LOG("FastSeek(%" PRId64 ") avgFrameLen=%f mNumParsedFrames=%" PRIu64
+         " mFrameIndex=%" PRId64 " mOffset=%" PRIu64,
+         aTime.ToMicroseconds(), AverageFrameLength(), mNumParsedFrames,
+         mFrameIndex, mOffset);
+
+  const auto& vbr = mParser.VBRInfo();
+  if (!aTime.ToMicroseconds()) {
+    // Quick seek to the beginning of the stream.
+    mFrameIndex = 0;
+  } else if (vbr.IsTOCPresent() && Duration().ToMicroseconds() > 0) {
+    // Use TOC for more precise seeking.
+    const float durationFrac = static_cast<float>(aTime.ToMicroseconds()) /
+                                                  Duration().ToMicroseconds();
+    mFrameIndex = FrameIndexFromOffset(vbr.Offset(durationFrac));
+  } else if (AverageFrameLength() > 0) {
+    mFrameIndex = FrameIndexFromTime(aTime);
+  }
+
+  mOffset = OffsetFromFrameIndex(mFrameIndex);
+
+  if (mOffset > mFirstFrameOffset && StreamLength() > 0) {
+    mOffset = std::min(StreamLength() - 1, mOffset);
+  }
+
+  mParser.EndFrameSession();
+
+  MP3LOG("FastSeek End TOC=%d avgFrameLen=%f mNumParsedFrames=%" PRIu64
+         " mFrameIndex=%" PRId64 " mFirstFrameOffset=%llu mOffset=%" PRIu64
+         " SL=%llu NumBytes=%u",
+         vbr.IsTOCPresent(), AverageFrameLength(), mNumParsedFrames, mFrameIndex,
+         mFirstFrameOffset, mOffset, StreamLength(), vbr.NumBytes().valueOr(0));
+
+  return Duration(mFrameIndex);
+}
+
+TimeUnit
+MP3TrackDemuxer::ScanUntil(const TimeUnit& aTime) {
+  MP3LOG("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);
+  }
+
+  if (Duration(mFrameIndex + 1) > aTime) {
+    return SeekPosition();
+  }
+
+  MediaByteRange nextRange = FindNextFrame();
+  while (SkipNextFrame(nextRange) && Duration(mFrameIndex + 1) < aTime) {
+    nextRange = FindNextFrame();
+    MP3LOGV("ScanUntil* avgFrameLen=%f mNumParsedFrames=%" PRIu64
+            " mFrameIndex=%" PRId64 " mOffset=%" PRIu64 " Duration=%" PRId64,
+            AverageFrameLength(), mNumParsedFrames,
+            mFrameIndex, mOffset, Duration(mFrameIndex + 1).ToMicroseconds());
+  }
+
+  MP3LOG("ScanUntil End avgFrameLen=%f mNumParsedFrames=%" PRIu64
+         " mFrameIndex=%" PRId64 " mOffset=%" PRIu64,
+         AverageFrameLength(), mNumParsedFrames, mFrameIndex, mOffset);
+
+  return SeekPosition();
+}
+
+RefPtr<MP3TrackDemuxer::SamplesPromise>
+MP3TrackDemuxer::GetSamples(int32_t aNumSamples) {
+  MP3LOGV("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);
+
+  if (!aNumSamples) {
+    return SamplesPromise::CreateAndReject(
+        NS_ERROR_DOM_MEDIA_DEMUXER_ERR, __func__);
+  }
+
+  RefPtr<SamplesHolder> frames = new SamplesHolder();
+
+  while (aNumSamples--) {
+    RefPtr<MediaRawData> frame(GetNextFrame(FindNextFrame()));
+    if (!frame) {
+      break;
+    }
+
+    frames->mSamples.AppendElement(frame);
+  }
+
+  MP3LOGV("GetSamples() End mSamples.Size()=%d aNumSamples=%d mOffset=%" PRIu64
+          " mNumParsedFrames=%" PRIu64 " mFrameIndex=%" PRId64
+          " mTotalFrameLen=%" PRIu64 " mSamplesPerFrame=%d mSamplesPerSecond=%d "
+          "mChannels=%d",
+          frames->mSamples.Length(), aNumSamples, mOffset, mNumParsedFrames,
+          mFrameIndex, mTotalFrameLen, mSamplesPerFrame, mSamplesPerSecond,
+          mChannels);
+
+  if (frames->mSamples.IsEmpty()) {
+    return SamplesPromise::CreateAndReject(
+        NS_ERROR_DOM_MEDIA_END_OF_STREAM, __func__);
+  }
+  return SamplesPromise::CreateAndResolve(frames, __func__);
+}
+
+void
+MP3TrackDemuxer::Reset() {
+  MP3LOG("Reset()");
+
+  FastSeek(TimeUnit());
+  mParser.Reset();
+}
+
+RefPtr<MP3TrackDemuxer::SkipAccessPointPromise>
+MP3TrackDemuxer::SkipToNextRandomAccessPoint(TimeUnit aTimeThreshold) {
+  // Will not be called for audio-only resources.
+  return SkipAccessPointPromise::CreateAndReject(
+    SkipFailureHolder(NS_ERROR_DOM_MEDIA_DEMUXER_ERR, 0), __func__);
+}
+
+int64_t
+MP3TrackDemuxer::GetResourceOffset() const {
+  return mOffset;
+}
+
+TimeIntervals
+MP3TrackDemuxer::GetBuffered() {
+  AutoPinned<MediaResource> stream(mSource.GetResource());
+  TimeIntervals buffered;
+
+  if (Duration() > TimeUnit() && stream->IsDataCachedToEndOfResource(0)) {
+    // Special case completely cached files. This also handles local files.
+    buffered += TimeInterval(TimeUnit(), Duration());
+    MP3LOGV("buffered = [[%" PRId64 ", %" PRId64 "]]",
+            TimeUnit().ToMicroseconds(), Duration().ToMicroseconds());
+    return buffered;
+  }
+
+  MediaByteRangeSet ranges;
+  nsresult rv = stream->GetCachedRanges(ranges);
+  NS_ENSURE_SUCCESS(rv, buffered);
+
+  for (const auto& range: ranges) {
+    if (range.IsEmpty()) {
+      continue;
+    }
+    TimeUnit start = Duration(FrameIndexFromOffset(range.mStart));
+    TimeUnit end = Duration(FrameIndexFromOffset(range.mEnd));
+    MP3LOGV("buffered += [%" PRId64 ", %" PRId64 "]",
+            start.ToMicroseconds(), end.ToMicroseconds());
+    buffered += TimeInterval(start, end);
+  }
+
+  return buffered;
+}
+
+int64_t
+MP3TrackDemuxer::StreamLength() const {
+  return mSource.GetLength();
+}
+
+TimeUnit
+MP3TrackDemuxer::Duration() const {
+  if (!mNumParsedFrames) {
+    return TimeUnit::FromMicroseconds(-1);
+  }
+
+  int64_t numFrames = 0;
+  const auto numAudioFrames = mParser.VBRInfo().NumAudioFrames();
+  if (mParser.VBRInfo().IsValid() && numAudioFrames.valueOr(0) + 1 > 1) {
+    // VBR headers don't include the VBR header frame.
+    numFrames = numAudioFrames.value() + 1;
+  } else {
+    const int64_t streamLen = StreamLength();
+    if (streamLen < 0) {
+      // Unknown length, we can't estimate duration.
+      return TimeUnit::FromMicroseconds(-1);
+    }
+    if (AverageFrameLength() > 0) {
+      numFrames = (streamLen - mFirstFrameOffset) / AverageFrameLength();
+    }
+  }
+  return Duration(numFrames);
+}
+
+TimeUnit
+MP3TrackDemuxer::Duration(int64_t aNumFrames) const {
+  if (!mSamplesPerSecond) {
+    return TimeUnit::FromMicroseconds(-1);
+  }
+
+  const double usPerFrame = USECS_PER_S * mSamplesPerFrame / mSamplesPerSecond;
+  return TimeUnit::FromMicroseconds(aNumFrames * usPerFrame);
+}
+
+MediaByteRange
+MP3TrackDemuxer::FindFirstFrame() {
+  static const int MIN_SUCCESSIVE_FRAMES = 4;
+
+  MediaByteRange candidateFrame = FindNextFrame();
+  int numSuccFrames = candidateFrame.Length() > 0;
+  MediaByteRange currentFrame = candidateFrame;
+  MP3LOGV("FindFirst() first candidate frame: mOffset=%" PRIu64 " Length()=%" PRIu64,
+          candidateFrame.mStart, candidateFrame.Length());
+
+  while (candidateFrame.Length() && numSuccFrames < MIN_SUCCESSIVE_FRAMES) {
+    mParser.EndFrameSession();
+    mOffset = currentFrame.mEnd;
+    const MediaByteRange prevFrame = currentFrame;
+
+    // FindNextFrame() here will only return frames consistent with our candidate frame.
+    currentFrame = FindNextFrame();
+    numSuccFrames += currentFrame.Length() > 0;
+    // Multiple successive false positives, which wouldn't be caught by the consistency
+    // checks alone, can be detected by wrong alignment (non-zero gap between frames).
+    const int64_t frameSeparation = currentFrame.mStart - prevFrame.mEnd;
+
+    if (!currentFrame.Length() || frameSeparation != 0) {
+      MP3LOGV("FindFirst() not enough successive frames detected, "
+              "rejecting candidate frame: successiveFrames=%d, last Length()=%" PRIu64
+              ", last frameSeparation=%" PRId64, numSuccFrames, currentFrame.Length(),
+              frameSeparation);
+
+      mParser.ResetFrameData();
+      mOffset = candidateFrame.mStart + 1;
+      candidateFrame = FindNextFrame();
+      numSuccFrames = candidateFrame.Length() > 0;
+      currentFrame = candidateFrame;
+      MP3LOGV("FindFirst() new candidate frame: mOffset=%" PRIu64 " Length()=%" PRIu64,
+              candidateFrame.mStart, candidateFrame.Length());
+    }
+  }
+
+  if (numSuccFrames >= MIN_SUCCESSIVE_FRAMES) {
+    MP3LOG("FindFirst() accepting candidate frame: "
+            "successiveFrames=%d", numSuccFrames);
+  } else {
+    MP3LOG("FindFirst() no suitable first frame found");
+  }
+  return candidateFrame;
+}
+
+static bool
+VerifyFrameConsistency(
+    const FrameParser::Frame& aFrame1, const FrameParser::Frame& aFrame2) {
+  const auto& h1 = aFrame1.Header();
+  const auto& h2 = aFrame2.Header();
+
+  return h1.IsValid() && h2.IsValid() &&
+         h1.Layer() == h2.Layer() &&
+         h1.SlotSize() == h2.SlotSize() &&
+         h1.SamplesPerFrame() == h2.SamplesPerFrame() &&
+         h1.Channels() == h2.Channels() &&
+         h1.SampleRate() == h2.SampleRate() &&
+         h1.RawVersion() == h2.RawVersion() &&
+         h1.RawProtection() == h2.RawProtection();
+}
+
+MediaByteRange
+MP3TrackDemuxer::FindNextFrame() {
+  static const int BUFFER_SIZE = 64;
+  static const int MAX_SKIPPED_BYTES = 1024 * BUFFER_SIZE;
+
+  MP3LOGV("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];
+  int32_t read = 0;
+
+  bool foundFrame = false;
+  int64_t frameHeaderOffset = 0;
+
+  // Check whether we've found a valid MPEG frame.
+  while (!foundFrame) {
+    if ((!mParser.FirstFrame().Length() &&
+         mOffset - mParser.ID3Header().Size() > MAX_SKIPPED_BYTES) ||
+        (read = Read(buffer, mOffset, BUFFER_SIZE)) == 0) {
+      MP3LOG("FindNext() EOS or exceeded MAX_SKIPPED_BYTES without a frame");
+      // This is not a valid MPEG audio stream or we've reached EOS, give up.
+      break;
+    }
+
+    ByteReader reader(buffer, read);
+    uint32_t bytesToSkip = 0;
+    foundFrame = mParser.Parse(&reader, &bytesToSkip);
+    frameHeaderOffset = mOffset + reader.Offset() - FrameParser::FrameHeader::SIZE;
+
+    // If we've found neither an MPEG frame header nor an ID3v2 tag,
+    // the reader shouldn't have any bytes remaining.
+    MOZ_ASSERT(foundFrame || bytesToSkip || !reader.Remaining());
+
+    if (foundFrame && mParser.FirstFrame().Length() &&
+        !VerifyFrameConsistency(mParser.FirstFrame(), mParser.CurrentFrame())) {
+      // We've likely hit a false-positive, ignore it and proceed with the
+      // search for the next valid frame.
+      foundFrame = false;
+      mOffset = frameHeaderOffset + 1;
+      mParser.EndFrameSession();
+    } else {
+      // Advance mOffset by the amount of bytes read and if necessary,
+      // skip an ID3v2 tag which stretches beyond the current buffer.
+      NS_ENSURE_TRUE(mOffset + read + bytesToSkip > mOffset,
+                     MediaByteRange(0, 0));
+      mOffset += read + bytesToSkip;
+    }
+  }
+
+  if (!foundFrame || !mParser.CurrentFrame().Length()) {
+    MP3LOG("FindNext() Exit foundFrame=%d mParser.CurrentFrame().Length()=%d ",
+           foundFrame, mParser.CurrentFrame().Length());
+    return { 0, 0 };
+  }
+
+  MP3LOGV("FindNext() End mOffset=%" PRIu64 " mNumParsedFrames=%" PRIu64
+          " mFrameIndex=%" PRId64 " frameHeaderOffset=%d"
+          " mTotalFrameLen=%" PRIu64 " mSamplesPerFrame=%d mSamplesPerSecond=%d"
+          " mChannels=%d",
+          mOffset, mNumParsedFrames, mFrameIndex, frameHeaderOffset,
+          mTotalFrameLen, mSamplesPerFrame, mSamplesPerSecond, mChannels);
+
+  return { frameHeaderOffset, frameHeaderOffset + mParser.CurrentFrame().Length() };
+}
+
+bool
+MP3TrackDemuxer::SkipNextFrame(const MediaByteRange& aRange) {
+  if (!mNumParsedFrames || !aRange.Length()) {
+    // We can't skip the first frame, since it could contain VBR headers.
+    RefPtr<MediaRawData> frame(GetNextFrame(aRange));
+    return frame;
+  }
+
+  UpdateState(aRange);
+
+  MP3LOGV("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>
+MP3TrackDemuxer::GetNextFrame(const MediaByteRange& aRange) {
+  MP3LOG("GetNext() Begin({mStart=%" PRId64 " Length()=%" PRId64 "})",
+         aRange.mStart, aRange.Length());
+  if (!aRange.Length()) {
+    return nullptr;
+  }
+
+  RefPtr<MediaRawData> frame = new MediaRawData();
+  frame->mOffset = aRange.mStart;
+
+  nsAutoPtr<MediaRawDataWriter> frameWriter(frame->CreateWriter());
+  if (!frameWriter->SetSize(aRange.Length())) {
+    MP3LOG("GetNext() Exit failed to allocated media buffer");
+    return nullptr;
+  }
+
+  const uint32_t read = Read(frameWriter->Data(), frame->mOffset, frame->Size());
+
+  if (read != aRange.Length()) {
+    MP3LOG("GetNext() Exit read=%u frame->Size()=%u", read, frame->Size());
+    return nullptr;
+  }
+
+  UpdateState(aRange);
+
+  frame->mTime = Duration(mFrameIndex - 1).ToMicroseconds();
+  frame->mDuration = Duration(1).ToMicroseconds();
+  frame->mTimecode = frame->mTime;
+  frame->mKeyframe = true;
+
+  MOZ_ASSERT(frame->mTime >= 0);
+  MOZ_ASSERT(frame->mDuration > 0);
+
+  if (mNumParsedFrames == 1) {
+    // First frame parsed, let's read VBR info if available.
+    ByteReader reader(frame->Data(), frame->Size());
+    mParser.ParseVBRHeader(&reader);
+    mFirstFrameOffset = frame->mOffset;
+  }
+
+  MP3LOGV("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
+MP3TrackDemuxer::OffsetFromFrameIndex(int64_t aFrameIndex) const {
+  int64_t offset = 0;
+  const auto& vbr = mParser.VBRInfo();
+
+  if (vbr.IsComplete()) {
+    offset = mFirstFrameOffset + aFrameIndex * vbr.NumBytes().value() /
+             vbr.NumAudioFrames().value();
+  } else if (AverageFrameLength() > 0) {
+    offset = mFirstFrameOffset + aFrameIndex * AverageFrameLength();
+  }
+
+  MP3LOGV("OffsetFromFrameIndex(%" PRId64 ") -> %" PRId64, aFrameIndex, offset);
+  return std::max<int64_t>(mFirstFrameOffset, offset);
+}
+
+int64_t
+MP3TrackDemuxer::FrameIndexFromOffset(int64_t aOffset) const {
+  int64_t frameIndex = 0;
+  const auto& vbr = mParser.VBRInfo();
+
+  if (vbr.IsComplete()) {
+    frameIndex = static_cast<float>(aOffset - mFirstFrameOffset) /
+                 vbr.NumBytes().value() * vbr.NumAudioFrames().value();
+    frameIndex = std::min<int64_t>(vbr.NumAudioFrames().value(), frameIndex);
+  } else if (AverageFrameLength() > 0) {
+    frameIndex = (aOffset - mFirstFrameOffset) / AverageFrameLength();
+  }
+
+  MP3LOGV("FrameIndexFromOffset(%" PRId64 ") -> %" PRId64, aOffset, frameIndex);
+  return std::max<int64_t>(0, frameIndex);
+}
+
+int64_t
+MP3TrackDemuxer::FrameIndexFromTime(const media::TimeUnit& aTime) const {
+  int64_t frameIndex = 0;
+  if (mSamplesPerSecond > 0 && mSamplesPerFrame > 0) {
+    frameIndex = aTime.ToSeconds() * mSamplesPerSecond / mSamplesPerFrame - 1;
+  }
+
+  MP3LOGV("FrameIndexFromOffset(%fs) -> %" PRId64, aTime.ToSeconds(), frameIndex);
+  return std::max<int64_t>(0, frameIndex);
+}
+
+void
+MP3TrackDemuxer::UpdateState(const MediaByteRange& aRange) {
+  // Prevent overflow.
+  if (mTotalFrameLen + aRange.Length() < 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 = aRange.mEnd;
+
+  mTotalFrameLen += aRange.Length();
+
+  if (!mSamplesPerFrame) {
+    mSamplesPerFrame = mParser.CurrentFrame().Header().SamplesPerFrame();
+    mSamplesPerSecond = mParser.CurrentFrame().Header().SampleRate();
+    mChannels = mParser.CurrentFrame().Header().Channels();
+  }
+
+  ++mNumParsedFrames;
+  ++mFrameIndex;
+  MOZ_ASSERT(mFrameIndex > 0);
+
+  // Prepare the parser for the next frame parsing session.
+  mParser.EndFrameSession();
+}
+
+int32_t
+MP3TrackDemuxer::Read(uint8_t* aBuffer, int64_t aOffset, int32_t aSize) {
+  MP3LOGV("MP3TrackDemuxer::Read(%p %" PRId64 " %d)", aBuffer, aOffset, aSize);
+
+  const int64_t streamLen = StreamLength();
+  if (mInfo && streamLen > 0) {
+    // Prevent blocking reads after successful initialization.
+    aSize = std::min<int64_t>(aSize, streamLen - aOffset);
+  }
+
+  uint32_t read = 0;
+  MP3LOGV("MP3TrackDemuxer::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 static_cast<int32_t>(read);
+}
+
+double
+MP3TrackDemuxer::AverageFrameLength() const {
+  if (mNumParsedFrames) {
+    return static_cast<double>(mTotalFrameLen) / mNumParsedFrames;
+  }
+  const auto& vbr = mParser.VBRInfo();
+  if (vbr.IsComplete() && vbr.NumAudioFrames().value() + 1) {
+    return static_cast<double>(vbr.NumBytes().value()) /
+           (vbr.NumAudioFrames().value() + 1);
+  }
+  return 0.0;
+}
+
+// FrameParser
+
+namespace frame_header {
+// FrameHeader mRaw byte offsets.
+static const int SYNC1 = 0;
+static const int SYNC2_VERSION_LAYER_PROTECTION = 1;
+static const int BITRATE_SAMPLERATE_PADDING_PRIVATE = 2;
+static const int CHANNELMODE_MODEEXT_COPY_ORIG_EMPH = 3;
+} // namespace frame_header
+
+FrameParser::FrameParser()
+{
+}
+
+void
+FrameParser::Reset() {
+  mID3Parser.Reset();
+  mFrame.Reset();
+}
+
+void
+FrameParser::ResetFrameData() {
+  mFrame.Reset();
+  mFirstFrame.Reset();
+  mPrevFrame.Reset();
+}
+
+void
+FrameParser::EndFrameSession() {
+  if (!mID3Parser.Header().IsValid()) {
+    // Reset ID3 tags only if we have not parsed a valid ID3 header yet.
+    mID3Parser.Reset();
+  }
+  mPrevFrame = mFrame;
+  mFrame.Reset();
+}
+
+const FrameParser::Frame&
+FrameParser::CurrentFrame() const {
+  return mFrame;
+}
+
+const FrameParser::Frame&
+FrameParser::PrevFrame() const {
+  return mPrevFrame;
+}
+
+const FrameParser::Frame&
+FrameParser::FirstFrame() const {
+  return mFirstFrame;
+}
+
+const ID3Parser::ID3Header&
+FrameParser::ID3Header() const {
+  return mID3Parser.Header();
+}
+
+const FrameParser::VBRHeader&
+FrameParser::VBRInfo() const {
+  return mVBRHeader;
+}
+
+bool
+FrameParser::Parse(ByteReader* aReader, uint32_t* aBytesToSkip) {
+  MOZ_ASSERT(aReader && aBytesToSkip);
+  *aBytesToSkip = 0;
+
+  if (!mID3Parser.Header().Size() && !mFirstFrame.Length()) {
+    // No MP3 frames have been parsed yet, look for ID3v2 headers at file begin.
+    // ID3v1 tags may only be at file end.
+    // TODO: should we try to read ID3 tags at end of file/mid-stream, too?
+    const size_t prevReaderOffset = aReader->Offset();
+    const uint32_t tagSize = mID3Parser.Parse(aReader);
+    if (tagSize) {
+      // ID3 tag found, skip past it.
+      const uint32_t skipSize = tagSize - ID3Parser::ID3Header::SIZE;
+
+      if (skipSize > aReader->Remaining()) {
+        // Skipping across the ID3v2 tag would take us past the end of the buffer, therefore we
+        // return immediately and let the calling function handle skipping the rest of the tag.
+        MP3LOGV("ID3v2 tag detected, size=%d,"
+                " needing to skip %d bytes past the current buffer",
+                tagSize, skipSize - aReader->Remaining());
+        *aBytesToSkip = skipSize - aReader->Remaining();
+        return false;
+      }
+      MP3LOGV("ID3v2 tag detected, size=%d", tagSize);
+      aReader->Read(skipSize);
+    } else {
+      // No ID3v2 tag found, rewinding reader in order to search for a MPEG frame header.
+      aReader->Seek(prevReaderOffset);
+    }
+  }
+
+  while (aReader->CanRead8() && !mFrame.ParseNext(aReader->ReadU8())) { }
+
+  if (mFrame.Length()) {
+    // MP3 frame found.
+    if (!mFirstFrame.Length()) {
+      mFirstFrame = mFrame;
+    }
+    // Indicate success.
+    return true;
+  }
+  return false;
+}
+
+// FrameParser::Header
+
+FrameParser::FrameHeader::FrameHeader()
+{
+  Reset();
+}
+
+uint8_t
+FrameParser::FrameHeader::Sync1() const {
+  return mRaw[frame_header::SYNC1];
+}
+
+uint8_t
+FrameParser::FrameHeader::Sync2() const {
+  return 0x7 & mRaw[frame_header::SYNC2_VERSION_LAYER_PROTECTION] >> 5;
+}
+
+uint8_t
+FrameParser::FrameHeader::RawVersion() const {
+  return 0x3 & mRaw[frame_header::SYNC2_VERSION_LAYER_PROTECTION] >> 3;
+}
+
+uint8_t
+FrameParser::FrameHeader::RawLayer() const {
+  return 0x3 & mRaw[frame_header::SYNC2_VERSION_LAYER_PROTECTION] >> 1;
+}
+
+uint8_t
+FrameParser::FrameHeader::RawProtection() const {
+  return 0x1 & mRaw[frame_header::SYNC2_VERSION_LAYER_PROTECTION] >> 6;
+}
+
+uint8_t
+FrameParser::FrameHeader::RawBitrate() const {
+  return 0xF & mRaw[frame_header::BITRATE_SAMPLERATE_PADDING_PRIVATE] >> 4;
+}
+
+uint8_t
+FrameParser::FrameHeader::RawSampleRate() const {
+  return 0x3 & mRaw[frame_header::BITRATE_SAMPLERATE_PADDING_PRIVATE] >> 2;
+}
+
+uint8_t
+FrameParser::FrameHeader::Padding() const {
+  return 0x1 & mRaw[frame_header::BITRATE_SAMPLERATE_PADDING_PRIVATE] >> 1;
+}
+
+uint8_t
+FrameParser::FrameHeader::Private() const {
+  return 0x1 & mRaw[frame_header::BITRATE_SAMPLERATE_PADDING_PRIVATE];
+}
+
+uint8_t
+FrameParser::FrameHeader::RawChannelMode() const {
+  return 0x3 & mRaw[frame_header::CHANNELMODE_MODEEXT_COPY_ORIG_EMPH] >> 6;
+}
+
+int32_t
+FrameParser::FrameHeader::Layer() const {
+  static const uint8_t LAYERS[4] = { 0, 3, 2, 1 };
+
+  return LAYERS[RawLayer()];
+}
+
+int32_t
+FrameParser::FrameHeader::SampleRate() const {
+  // Sample rates - use [version][srate]
+  static const uint16_t SAMPLE_RATE[4][4] = {
+    { 11025, 12000,  8000, 0 }, // MPEG 2.5
+    {     0,     0,     0, 0 }, // Reserved
+    { 22050, 24000, 16000, 0 }, // MPEG 2
+    { 44100, 48000, 32000, 0 }  // MPEG 1
+  };
+
+  return SAMPLE_RATE[RawVersion()][RawSampleRate()];
+}
+
+int32_t
+FrameParser::FrameHeader::Channels() const {
+  // 3 is single channel (mono), any other value is some variant of dual
+  // channel.
+  return RawChannelMode() == 3 ? 1 : 2;
+}
+
+int32_t
+FrameParser::FrameHeader::SamplesPerFrame() const {
+  // Samples per frame - use [version][layer]
+  static const uint16_t FRAME_SAMPLE[4][4] = {
+    // Layer     3     2     1       Version
+    {      0,  576, 1152,  384 }, // 2.5
+    {      0,    0,    0,    0 }, // Reserved
+    {      0,  576, 1152,  384 }, // 2
+    {      0, 1152, 1152,  384 }  // 1
+  };
+
+  return FRAME_SAMPLE[RawVersion()][RawLayer()];
+}
+
+int32_t
+FrameParser::FrameHeader::Bitrate() const {
+  // Bitrates - use [version][layer][bitrate]
+  static const uint16_t BITRATE[4][4][16] = {
+    { // Version 2.5
+      { 0,   0,   0,   0,   0,   0,   0,   0,   0,   0,   0,   0,   0,   0,   0, 0 }, // Reserved
+      { 0,   8,  16,  24,  32,  40,  48,  56,  64,  80,  96, 112, 128, 144, 160, 0 }, // Layer 3
+      { 0,   8,  16,  24,  32,  40,  48,  56,  64,  80,  96, 112, 128, 144, 160, 0 }, // Layer 2
+      { 0,  32,  48,  56,  64,  80,  96, 112, 128, 144, 160, 176, 192, 224, 256, 0 }  // Layer 1
+    },
+    { // Reserved
+      { 0,   0,   0,   0,   0,   0,   0,   0,   0,   0,   0,   0,   0,   0,   0, 0 }, // Invalid
+      { 0,   0,   0,   0,   0,   0,   0,   0,   0,   0,   0,   0,   0,   0,   0, 0 }, // Invalid
+      { 0,   0,   0,   0,   0,   0,   0,   0,   0,   0,   0,   0,   0,   0,   0, 0 }, // Invalid
+      { 0,   0,   0,   0,   0,   0,   0,   0,   0,   0,   0,   0,   0,   0,   0, 0 }  // Invalid
+    },
+    { // Version 2
+      { 0,   0,   0,   0,   0,   0,   0,   0,   0,   0,   0,   0,   0,   0,   0, 0 }, // Reserved
+      { 0,   8,  16,  24,  32,  40,  48,  56,  64,  80,  96, 112, 128, 144, 160, 0 }, // Layer 3
+      { 0,   8,  16,  24,  32,  40,  48,  56,  64,  80,  96, 112, 128, 144, 160, 0 }, // Layer 2
+      { 0,  32,  48,  56,  64,  80,  96, 112, 128, 144, 160, 176, 192, 224, 256, 0 }  // Layer 1
+    },
+    { // Version 1
+      { 0,   0,   0,   0,   0,   0,   0,   0,   0,   0,   0,   0,   0,   0,   0, 0 }, // Reserved
+      { 0,  32,  40,  48,  56,  64,  80,  96, 112, 128, 160, 192, 224, 256, 320, 0 }, // Layer 3
+      { 0,  32,  48,  56,  64,  80,  96, 112, 128, 160, 192, 224, 256, 320, 384, 0 }, // Layer 2
+      { 0,  32,  64,  96, 128, 160, 192, 224, 256, 288, 320, 352, 384, 416, 448, 0 }, // Layer 1
+    }
+  };
+
+  return 1000 * BITRATE[RawVersion()][RawLayer()][RawBitrate()];
+}
+
+int32_t
+FrameParser::FrameHeader::SlotSize() const {
+  // Slot size (MPEG unit of measurement) - use [layer]
+  static const uint8_t SLOT_SIZE[4] = { 0, 1, 1, 4 }; // Rsvd, 3, 2, 1
+
+  return SLOT_SIZE[RawLayer()];
+}
+
+bool
+FrameParser::FrameHeader::ParseNext(uint8_t c) {
+  if (!Update(c)) {
+    Reset();
+    if (!Update(c)) {
+      Reset();
+    }
+  }
+  return IsValid();
+}
+
+bool
+FrameParser::FrameHeader::IsValid(int aPos) const {
+  if (aPos >= SIZE) {
+    return true;
+  }
+  if (aPos == frame_header::SYNC1) {
+    return Sync1() == 0xFF;
+  }
+  if (aPos == frame_header::SYNC2_VERSION_LAYER_PROTECTION) {
+    return Sync2() == 7 &&
+           RawVersion() != 1 &&
+           Layer() == 3;
+  }
+  if (aPos == frame_header::BITRATE_SAMPLERATE_PADDING_PRIVATE) {
+    return RawBitrate() != 0xF && RawBitrate() != 0 &&
+           RawSampleRate() != 3;
+  }
+  return true;
+}
+
+bool
+FrameParser::FrameHeader::IsValid() const {
+  return mPos >= SIZE;
+}
+
+void
+FrameParser::FrameHeader::Reset() {
+  mPos = 0;
+}
+
+bool
+FrameParser::FrameHeader::Update(uint8_t c) {
+  if (mPos < SIZE) {
+    mRaw[mPos] = c;
+  }
+  return IsValid(mPos++);
+}
+
+// FrameParser::VBRHeader
+
+namespace vbr_header {
+static const char* TYPE_STR[3] = {"NONE", "XING", "VBRI"};
+static const uint32_t TOC_SIZE = 100;
+} // namespace vbr_header
+
+FrameParser::VBRHeader::VBRHeader()
+  : mType(NONE)
+{
+}
+
+FrameParser::VBRHeader::VBRHeaderType
+FrameParser::VBRHeader::Type() const {
+  return mType;
+}
+
+const Maybe<uint32_t>&
+FrameParser::VBRHeader::NumAudioFrames() const {
+  return mNumAudioFrames;
+}
+
+const Maybe<uint32_t>&
+FrameParser::VBRHeader::NumBytes() const {
+  return mNumBytes;
+}
+
+const Maybe<uint32_t>&
+FrameParser::VBRHeader::Scale() const {
+  return mScale;
+}
+
+bool
+FrameParser::VBRHeader::IsTOCPresent() const {
+  return mTOC.size() == vbr_header::TOC_SIZE;
+}
+
+bool
+FrameParser::VBRHeader::IsValid() const {
+  return mType != NONE;
+}
+
+bool
+FrameParser::VBRHeader::IsComplete() const {
+  return IsValid() &&
+         mNumAudioFrames.valueOr(0) > 0 &&
+         mNumBytes.valueOr(0) > 0 &&
+         // We don't care about the scale for any computations here.
+         // mScale < 101 &&
+         true;
+}
+
+int64_t
+FrameParser::VBRHeader::Offset(float aDurationFac) const {
+  if (!IsTOCPresent()) {
+    return -1;
+  }
+
+  // Constrain the duration percentage to [0, 99].
+  const float durationPer = 100.0f * std::min(0.99f, std::max(0.0f, aDurationFac));
+  const size_t fullPer = durationPer;
+  const float rest = durationPer - fullPer;
+
+  MOZ_ASSERT(fullPer < mTOC.size());
+  int64_t offset = mTOC.at(fullPer);
+
+  if (rest > 0.0 && fullPer + 1 < mTOC.size()) {
+    offset += rest * (mTOC.at(fullPer + 1) - offset);
+  }
+
+  return offset;
+}
+
+bool
+FrameParser::VBRHeader::ParseXing(ByteReader* aReader) {
+  static const uint32_t XING_TAG = BigEndian::readUint32("Xing");
+  static const uint32_t INFO_TAG = BigEndian::readUint32("Info");
+
+  enum Flags {
+    NUM_FRAMES = 0x01,
+    NUM_BYTES = 0x02,
+    TOC = 0x04,
+    VBR_SCALE = 0x08
+  };
+
+  MOZ_ASSERT(aReader);
+  const size_t prevReaderOffset = aReader->Offset();
+
+  // We have to search for the Xing header as its position can change.
+  while (aReader->CanRead32() &&
+         aReader->PeekU32() != XING_TAG && aReader->PeekU32() != INFO_TAG) {
+    aReader->Read(1);
+  }
+
+  if (aReader->CanRead32()) {
+    // Skip across the VBR header ID tag.
+    aReader->ReadU32();
+    mType = XING;
+  }
+  uint32_t flags = 0;
+  if (aReader->CanRead32()) {
+    flags = aReader->ReadU32();
+  }
+  if (flags & NUM_FRAMES && aReader->CanRead32()) {
+    mNumAudioFrames = Some(aReader->ReadU32());
+  }
+  if (flags & NUM_BYTES && aReader->CanRead32()) {
+    mNumBytes = Some(aReader->ReadU32());
+  }
+  if (flags & TOC && aReader->Remaining() >= vbr_header::TOC_SIZE) {
+    if (!mNumBytes) {
+      // We don't have the stream size to calculate offsets, skip the TOC.
+      aReader->Read(vbr_header::TOC_SIZE);
+    } else {
+      mTOC.clear();
+      mTOC.reserve(vbr_header::TOC_SIZE);
+      for (size_t i = 0; i < vbr_header::TOC_SIZE; ++i) {
+        mTOC.push_back(1.0f / 256.0f * aReader->ReadU8() * mNumBytes.value());
+      }
+    }
+  }
+  if (flags & VBR_SCALE && aReader->CanRead32()) {
+    mScale = Some(aReader->ReadU32());
+  }
+
+  aReader->Seek(prevReaderOffset);
+  return mType == XING;
+}
+
+bool
+FrameParser::VBRHeader::ParseVBRI(ByteReader* aReader) {
+  static const uint32_t TAG = BigEndian::readUint32("VBRI");
+  static const uint32_t OFFSET = 32 + FrameParser::FrameHeader::SIZE;
+  static const uint32_t FRAME_COUNT_OFFSET = OFFSET + 14;
+  static const uint32_t MIN_FRAME_SIZE = OFFSET + 26;
+
+  MOZ_ASSERT(aReader);
+  // ParseVBRI assumes that the ByteReader offset points to the beginning of a frame,
+  // therefore as a simple check, we look for the presence of a frame sync at that position.
+  MOZ_ASSERT((aReader->PeekU16() & 0xFFE0) == 0xFFE0);
+  const size_t prevReaderOffset = aReader->Offset();
+
+  // VBRI have a fixed relative position, so let's check for it there.
+  if (aReader->Remaining() > MIN_FRAME_SIZE) {
+    aReader->Seek(prevReaderOffset + OFFSET);
+    if (aReader->ReadU32() == TAG) {
+      aReader->Seek(prevReaderOffset + FRAME_COUNT_OFFSET);
+      mNumAudioFrames = Some(aReader->ReadU32());
+      mType = VBRI;
+      aReader->Seek(prevReaderOffset);
+      return true;
+    }
+  }
+  aReader->Seek(prevReaderOffset);
+  return false;
+}
+
+bool
+FrameParser::VBRHeader::Parse(ByteReader* aReader) {
+  const bool rv = ParseVBRI(aReader) || ParseXing(aReader);
+  if (rv) {
+    MP3LOG("VBRHeader::Parse found valid VBR/CBR header: type=%s"
+           " NumAudioFrames=%u NumBytes=%u Scale=%u TOC-size=%u",
+           vbr_header::TYPE_STR[Type()], NumAudioFrames().valueOr(0),
+           NumBytes().valueOr(0), Scale().valueOr(0), mTOC.size());
+  }
+  return rv;
+}
+
+// FrameParser::Frame
+
+void
+FrameParser::Frame::Reset() {
+  mHeader.Reset();
+}
+
+int32_t
+FrameParser::Frame::Length() const {
+  if (!mHeader.IsValid() || !mHeader.SampleRate()) {
+    return 0;
+  }
+
+  const float bitsPerSample = mHeader.SamplesPerFrame() / 8.0f;
+  const int32_t frameLen = bitsPerSample * mHeader.Bitrate() /
+                           mHeader.SampleRate() +
+                           mHeader.Padding() * mHeader.SlotSize();
+  return frameLen;
+}
+
+bool
+FrameParser::Frame::ParseNext(uint8_t c) {
+  return mHeader.ParseNext(c);
+}
+
+const FrameParser::FrameHeader&
+FrameParser::Frame::Header() const {
+  return mHeader;
+}
+
+bool
+FrameParser::ParseVBRHeader(ByteReader* aReader) {
+  return mVBRHeader.Parse(aReader);
+}
+
+// ID3Parser
+
+// Constants
+namespace id3_header {
+static const int ID_LEN = 3;
+static const int VERSION_LEN = 2;
+static const int FLAGS_LEN = 1;
+static const int SIZE_LEN = 4;
+
+static const int ID_END = ID_LEN;
+static const int VERSION_END = ID_END + VERSION_LEN;
+static const int FLAGS_END = VERSION_END + FLAGS_LEN;
+static const int SIZE_END = FLAGS_END + SIZE_LEN;
+
+static const uint8_t ID[ID_LEN] = {'I', 'D', '3'};
+
+static const uint8_t MIN_MAJOR_VER = 2;
+static const uint8_t MAX_MAJOR_VER = 4;
+} // namespace id3_header
+
+uint32_t
+ID3Parser::Parse(ByteReader* aReader) {
+  MOZ_ASSERT(aReader);
+
+  while (aReader->CanRead8() && !mHeader.ParseNext(aReader->ReadU8())) { }
+
+  if (mHeader.IsValid()) {
+    // Header found, return total tag size.
+    return ID3Header::SIZE + Header().Size() + Header().FooterSize();
+  }
+  return 0;
+}
+
+void
+ID3Parser::Reset() {
+  mHeader.Reset();
+}
+
+const ID3Parser::ID3Header&
+ID3Parser::Header() const {
+  return mHeader;
+}
+
+// ID3Parser::Header
+
+ID3Parser::ID3Header::ID3Header()
+{
+  Reset();
+}
+
+void
+ID3Parser::ID3Header::Reset() {
+  mSize = 0;
+  mPos = 0;
+}
+
+uint8_t
+ID3Parser::ID3Header::MajorVersion() const {
+  return mRaw[id3_header::ID_END];
+}
+
+uint8_t
+ID3Parser::ID3Header::MinorVersion() const {
+  return mRaw[id3_header::ID_END + 1];
+}
+
+uint8_t
+ID3Parser::ID3Header::Flags() const {
+  return mRaw[id3_header::FLAGS_END - id3_header::FLAGS_LEN];
+}
+
+uint32_t
+ID3Parser::ID3Header::Size() const {
+  if (!IsValid()) {
+    return 0;
+  }
+  return mSize;
+}
+
+uint8_t
+ID3Parser::ID3Header::FooterSize() const {
+  if (Flags() & (1 << 4)) {
+    return SIZE;
+  }
+  return 0;
+}
+
+bool
+ID3Parser::ID3Header::ParseNext(uint8_t c) {
+  if (!Update(c)) {
+    Reset();
+    if (!Update(c)) {
+      Reset();
+    }
+  }
+  return IsValid();
+}
+
+bool
+ID3Parser::ID3Header::IsValid(int aPos) const {
+  if (aPos >= SIZE) {
+    return true;
+  }
+  const uint8_t c = mRaw[aPos];
+  switch (aPos) {
+    case 0: case 1: case 2:
+      // Expecting "ID3".
+      return id3_header::ID[aPos] == c;
+    case 3:
+      return MajorVersion() >= id3_header::MIN_MAJOR_VER &&
+             MajorVersion() <= id3_header::MAX_MAJOR_VER;
+    case 4:
+      return MinorVersion() < 0xFF;
+    case 5:
+      // Validate flags for supported versions, see bug 949036.
+      return ((0xFF >> MajorVersion()) & c) == 0;
+    case 6: case 7: case 8: case 9:
+      return c < 0x80;
+  }
+  return true;
+}
+
+bool
+ID3Parser::ID3Header::IsValid() const {
+  return mPos >= SIZE;
+}
+
+bool
+ID3Parser::ID3Header::Update(uint8_t c) {
+  if (mPos >= id3_header::SIZE_END - id3_header::SIZE_LEN &&
+      mPos < id3_header::SIZE_END) {
+    mSize <<= 7;
+    mSize |= c;
+  }
+  if (mPos < SIZE) {
+    mRaw[mPos] = c;
+  }
+  return IsValid(mPos++);
+}
+
+} // namespace mozilla