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diff --git a/dom/media/mp3/MP3Demuxer.h b/dom/media/mp3/MP3Demuxer.h
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+++ b/dom/media/mp3/MP3Demuxer.h
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+/* 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/. */
+
+#ifndef MP3_DEMUXER_H_
+#define MP3_DEMUXER_H_
+
+#include "MediaDataDemuxer.h"
+#include "MediaResource.h"
+#include "MP3FrameParser.h"
+
+namespace mozilla {
+
+class MP3TrackDemuxer;
+
+DDLoggedTypeDeclNameAndBase(MP3Demuxer, MediaDataDemuxer);
+DDLoggedTypeNameAndBase(MP3TrackDemuxer, MediaTrackDemuxer);
+
+class MP3Demuxer : public MediaDataDemuxer,
+                   public DecoderDoctorLifeLogger<MP3Demuxer> {
+ public:
+  // MediaDataDemuxer interface.
+  explicit MP3Demuxer(MediaResource* aSource);
+  RefPtr<InitPromise> Init() override;
+  uint32_t GetNumberTracks(TrackInfo::TrackType aType) const override;
+  already_AddRefed<MediaTrackDemuxer> GetTrackDemuxer(
+      TrackInfo::TrackType aType, uint32_t aTrackNumber) override;
+  bool IsSeekable() const override;
+  void NotifyDataArrived() override;
+  void NotifyDataRemoved() override;
+
+ private:
+  // Synchronous initialization.
+  bool InitInternal();
+
+  RefPtr<MediaResource> mSource;
+  RefPtr<MP3TrackDemuxer> mTrackDemuxer;
+};
+
+// The MP3 demuxer used to extract MPEG frames and side information out of
+// MPEG streams.
+class MP3TrackDemuxer : public MediaTrackDemuxer,
+                        public DecoderDoctorLifeLogger<MP3TrackDemuxer> {
+ public:
+  // Constructor, expecting a valid media resource.
+  explicit MP3TrackDemuxer(MediaResource* aSource);
+
+  // Initializes the track demuxer by reading the first frame for meta data.
+  // Returns initialization success state.
+  bool Init();
+
+  // Returns the total stream length if known, -1 otherwise.
+  int64_t StreamLength() const;
+
+  // Returns the estimated stream duration, or a 0-duration if unknown.
+  media::NullableTimeUnit Duration() const;
+
+  // Returns the estimated duration up to the given frame number,
+  // or a 0-duration if unknown.
+  media::TimeUnit Duration(int64_t aNumFrames) const;
+
+  // Returns the estimated current seek position time.
+  media::TimeUnit SeekPosition() const;
+
+  const FrameParser::Frame& LastFrame() const;
+  RefPtr<MediaRawData> DemuxSample();
+
+  const ID3Parser::ID3Header& ID3Header() const;
+  const FrameParser::VBRHeader& VBRInfo() const;
+
+  // MediaTrackDemuxer interface.
+  UniquePtr<TrackInfo> GetInfo() const override;
+  RefPtr<SeekPromise> Seek(const media::TimeUnit& aTime) override;
+  RefPtr<SamplesPromise> GetSamples(int32_t aNumSamples = 1) override;
+  void Reset() override;
+  RefPtr<SkipAccessPointPromise> SkipToNextRandomAccessPoint(
+      const media::TimeUnit& aTimeThreshold) override;
+  int64_t GetResourceOffset() const override;
+  media::TimeIntervals GetBuffered() override;
+  // Return the duration in frames of the encoder delay.
+  uint32_t EncoderDelayFrames() const;
+  // Return the duration  in frames of the padding.
+  uint32_t PaddingFrames() const;
+
+ private:
+  // Destructor.
+  ~MP3TrackDemuxer() = default;
+
+  // Fast approximate seeking to given time.
+  media::TimeUnit FastSeek(const media::TimeUnit& aTime);
+
+  // Seeks by scanning the stream up to the given time for more accurate
+  // results.
+  media::TimeUnit ScanUntil(const media::TimeUnit& aTime);
+
+  // Finds the first valid frame and returns its byte range if found
+  // or a null-byte range otherwise.
+  MediaByteRange FindFirstFrame();
+
+  // Finds the next valid frame and returns its byte range if found
+  // or a null-byte range otherwise.
+  MediaByteRange FindNextFrame();
+
+  // Skips the next frame given the provided byte range.
+  bool SkipNextFrame(const MediaByteRange& aRange);
+
+  // Returns the next MPEG frame, if available.
+  already_AddRefed<MediaRawData> GetNextFrame(const MediaByteRange& aRange);
+
+  // Updates post-read meta data.
+  void UpdateState(const MediaByteRange& aRange);
+
+  // Returns the estimated offset for the given frame index.
+  int64_t OffsetFromFrameIndex(int64_t aFrameIndex) const;
+
+  // Returns the estimated frame index for the given offset.
+  int64_t FrameIndexFromOffset(int64_t aOffset) const;
+
+  // Returns the estimated frame index for the given time.
+  int64_t FrameIndexFromTime(const media::TimeUnit& aTime) const;
+
+  // Reads aSize bytes into aBuffer from the source starting at aOffset.
+  // Returns the actual size read.
+  uint32_t Read(uint8_t* aBuffer, int64_t aOffset, uint32_t aSize);
+
+  // Returns the average frame length derived from the previously parsed frames.
+  double AverageFrameLength() const;
+
+  // Returns the number of frames reported by the header if it's valid. Nothing
+  // otherwise.
+  Maybe<uint32_t> ValidNumAudioFrames() const;
+
+  // Return the duration of the encoder delay.
+  media::TimeUnit EncoderDelay() const;
+
+  // Return the duration of the padding.
+  media::TimeUnit Padding() const;
+
+  // The (hopefully) MPEG resource.
+  MediaResourceIndex mSource;
+
+  // MPEG frame parser used to detect frames and extract side info.
+  FrameParser mParser;
+
+  // Whether we've locked onto a valid sequence of frames or not.
+  bool mFrameLock;
+
+  // Current byte offset in the source stream.
+  int64_t mOffset;
+
+  // Byte offset of the begin of the first frame, or 0 if none parsed yet.
+  int64_t mFirstFrameOffset;
+
+  // Total parsed frames.
+  uint64_t mNumParsedFrames;
+
+  // Current frame index.
+  int64_t mFrameIndex;
+
+  // Sum of parsed frames' lengths in bytes.
+  int64_t mTotalFrameLen;
+
+  // Samples per frame metric derived from frame headers or 0 if none available.
+  uint32_t mSamplesPerFrame;
+
+  // Samples per second metric derived from frame headers or 0 if none
+  // available.
+  uint32_t mSamplesPerSecond;
+
+  // Channel count derived from frame headers or 0 if none available.
+  uint32_t mChannels;
+
+  // Audio track config info.
+  UniquePtr<AudioInfo> mInfo;
+
+  // Number of frames to skip at the beginning
+  uint32_t mEncoderDelay = 0;
+  // Number of frames to skip at the end
+  uint32_t mEncoderPadding = 0;
+  int32_t mRemainingEncoderPadding = 0;
+  // End of stream has been found
+  bool mEOS = false;
+};
+
+}  // namespace mozilla
+
+#endif