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diff --git a/dom/media/webm/WebMBufferedParser.h b/dom/media/webm/WebMBufferedParser.h
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+++ b/dom/media/webm/WebMBufferedParser.h
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+/* -*- 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/. */
+#if !defined(WebMBufferedParser_h_)
+#define WebMBufferedParser_h_
+
+#include "nsISupportsImpl.h"
+#include "nsTArray.h"
+#include "mozilla/ReentrantMonitor.h"
+#include "MediaResource.h"
+
+namespace mozilla {
+
+// Stores a stream byte offset and the scaled timecode of the block at
+// that offset.
+struct WebMTimeDataOffset
+{
+  WebMTimeDataOffset(int64_t aEndOffset, uint64_t aTimecode,
+                     int64_t aInitOffset, int64_t aSyncOffset,
+                     int64_t aClusterEndOffset)
+    : mEndOffset(aEndOffset)
+    , mInitOffset(aInitOffset)
+    , mSyncOffset(aSyncOffset)
+    , mClusterEndOffset(aClusterEndOffset)
+    , mTimecode(aTimecode)
+  {}
+
+  bool operator==(int64_t aEndOffset) const {
+    return mEndOffset == aEndOffset;
+  }
+
+  bool operator!=(int64_t aEndOffset) const {
+    return mEndOffset != aEndOffset;
+  }
+
+  bool operator<(int64_t aEndOffset) const {
+    return mEndOffset < aEndOffset;
+  }
+
+  int64_t mEndOffset;
+  int64_t mInitOffset;
+  int64_t mSyncOffset;
+  int64_t mClusterEndOffset;
+  uint64_t mTimecode;
+};
+
+// A simple WebM parser that produces data offset to timecode pairs as it
+// consumes blocks.  A new parser is created for each distinct range of data
+// received and begins parsing from the first WebM cluster within that
+// range.  Old parsers are destroyed when their range merges with a later
+// parser or an already parsed range.  The parser may start at any position
+// within the stream.
+struct WebMBufferedParser
+{
+  explicit WebMBufferedParser(int64_t aOffset)
+    : mStartOffset(aOffset)
+    , mCurrentOffset(aOffset)
+    , mInitEndOffset(-1)
+    , mBlockEndOffset(-1)
+    , mState(READ_ELEMENT_ID)
+    , mNextState(READ_ELEMENT_ID)
+    , mVIntRaw(false)
+    , mLastInitStartOffset(-1)
+    , mClusterSyncPos(0)
+    , mVIntLeft(0)
+    , mBlockSize(0)
+    , mClusterTimecode(0)
+    , mClusterOffset(0)
+    , mClusterEndOffset(-1)
+    , mBlockOffset(0)
+    , mBlockTimecode(0)
+    , mBlockTimecodeLength(0)
+    , mSkipBytes(0)
+    , mTimecodeScale(1000000)
+    , mGotTimecodeScale(false)
+  {
+    if (mStartOffset != 0) {
+      mState = FIND_CLUSTER_SYNC;
+    }
+  }
+
+  uint32_t GetTimecodeScale() {
+    MOZ_ASSERT(mGotTimecodeScale);
+    return mTimecodeScale;
+  }
+
+  // If this parser is not expected to parse a segment info, it must be told
+  // the appropriate timecode scale to use from elsewhere.
+  void SetTimecodeScale(uint32_t aTimecodeScale) {
+    mTimecodeScale = aTimecodeScale;
+    mGotTimecodeScale = true;
+  }
+
+  // Steps the parser through aLength bytes of data.  Always consumes
+  // aLength bytes.  Updates mCurrentOffset before returning.  Acquires
+  // aReentrantMonitor before using aMapping.
+  // Returns false if an error was encountered.
+  bool Append(const unsigned char* aBuffer, uint32_t aLength,
+              nsTArray<WebMTimeDataOffset>& aMapping,
+              ReentrantMonitor& aReentrantMonitor);
+
+  bool operator==(int64_t aOffset) const {
+    return mCurrentOffset == aOffset;
+  }
+
+  bool operator<(int64_t aOffset) const {
+    return mCurrentOffset < aOffset;
+  }
+
+  // Returns the start offset of the init (EBML) or media segment (Cluster)
+  // following the aOffset position. If none were found, returns mBlockEndOffset.
+  // This allows to determine the end of the interval containg aOffset.
+  int64_t EndSegmentOffset(int64_t aOffset);
+
+  // The offset at which this parser started parsing.  Used to merge
+  // adjacent parsers, in which case the later parser adopts the earlier
+  // parser's mStartOffset.
+  int64_t mStartOffset;
+
+  // Current offset within the stream.  Updated in chunks as Append() consumes
+  // data.
+  int64_t mCurrentOffset;
+
+  // Tracks element's end offset. This indicates the end of the first init
+  // segment. Will only be set if a Segment Information has been found.
+  int64_t mInitEndOffset;
+
+  // End offset of the last block parsed.
+  // Will only be set if a complete block has been parsed.
+  int64_t mBlockEndOffset;
+
+private:
+  enum State {
+    // Parser start state.  Expects to begin at a valid EBML element.  Move
+    // to READ_VINT with mVIntRaw true, then return to READ_ELEMENT_SIZE.
+    READ_ELEMENT_ID,
+
+    // Store element ID read into mVInt into mElement.mID.  Move to
+    // READ_VINT with mVIntRaw false, then return to PARSE_ELEMENT.
+    READ_ELEMENT_SIZE,
+
+    // Parser start state for parsers started at an arbitrary offset.  Scans
+    // forward for the first cluster, then move to READ_ELEMENT_ID.
+    FIND_CLUSTER_SYNC,
+
+    // Simplistic core of the parser.  Does not pay attention to nesting of
+    // elements.  Checks mElement for an element ID of interest, then moves
+    // to the next state as determined by the element ID.
+    PARSE_ELEMENT,
+
+    // Read the first byte of a variable length integer.  The first byte
+    // encodes both the variable integer's length and part of the value.
+    // The value read so far is stored in mVInt.mValue and the length is
+    // stored in mVInt.mLength.  The number of bytes left to read is stored
+    // in mVIntLeft.
+    READ_VINT,
+
+    // Reads the remaining mVIntLeft bytes into mVInt.mValue.
+    READ_VINT_REST,
+
+    // mVInt holds the parsed timecode scale, store it in mTimecodeScale,
+    // then return READ_ELEMENT_ID.
+    READ_TIMECODESCALE,
+
+    // mVInt holds the parsed cluster timecode, store it in
+    // mClusterTimecode, then return to READ_ELEMENT_ID.
+    READ_CLUSTER_TIMECODE,
+
+    // mBlockTimecodeLength holds the remaining length of the block timecode
+    // left to read.  Read each byte of the timecode into mBlockTimecode.
+    // Once complete, calculate the scaled timecode from the cluster
+    // timecode, block timecode, and timecode scale, and insert a
+    // WebMTimeDataOffset entry into aMapping if one is not already present
+    // for this offset.
+    READ_BLOCK_TIMECODE,
+
+    // Will skip the current tracks element and set mInitEndOffset if an init
+    // segment has been found.
+    // Currently, only assumes it's the end of the tracks element.
+    CHECK_INIT_FOUND,
+
+    // Skip mSkipBytes of data before resuming parse at mNextState.
+    SKIP_DATA,
+  };
+
+  // Current state machine action.
+  State mState;
+
+  // Next state machine action.  SKIP_DATA and READ_VINT_REST advance to
+  // mNextState when the current action completes.
+  State mNextState;
+
+  struct VInt {
+    VInt() : mValue(0), mLength(0) {}
+    uint64_t mValue;
+    uint64_t mLength;
+  };
+
+  struct EBMLElement {
+    uint64_t Length() { return mID.mLength + mSize.mLength; }
+    VInt mID;
+    VInt mSize;
+  };
+
+  EBMLElement mElement;
+
+  VInt mVInt;
+
+  bool mVIntRaw;
+
+  // EBML start offset. This indicates the start of the last init segment
+  // parsed. Will only be set if an EBML element has been found.
+  int64_t mLastInitStartOffset;
+
+  // Current match position within CLUSTER_SYNC_ID.  Used to find sync
+  // within arbitrary data.
+  uint32_t mClusterSyncPos;
+
+  // Number of bytes of mVInt left to read.  mVInt is complete once this
+  // reaches 0.
+  uint32_t mVIntLeft;
+
+  // Size of the block currently being parsed.  Any unused data within the
+  // block is skipped once the block timecode has been parsed.
+  uint64_t mBlockSize;
+
+  // Cluster-level timecode.
+  uint64_t mClusterTimecode;
+
+  // Start offset of the cluster currently being parsed.  Used as the sync
+  // point offset for the offset-to-time mapping as each block timecode is
+  // been parsed.
+  int64_t mClusterOffset;
+
+  // End offset of the cluster currently being parsed. -1 if unknown.
+  int64_t mClusterEndOffset;
+
+  // Start offset of the block currently being parsed.  Used as the byte
+  // offset for the offset-to-time mapping once the block timecode has been
+  // parsed.
+  int64_t mBlockOffset;
+
+  // Block-level timecode.  This is summed with mClusterTimecode to produce
+  // an absolute timecode for the offset-to-time mapping.
+  int16_t mBlockTimecode;
+
+  // Number of bytes of mBlockTimecode left to read.
+  uint32_t mBlockTimecodeLength;
+
+  // Count of bytes left to skip before resuming parse at mNextState.
+  // Mostly used to skip block payload data after reading a block timecode.
+  uint32_t mSkipBytes;
+
+  // Timecode scale read from the segment info and used to scale absolute
+  // timecodes.
+  uint32_t mTimecodeScale;
+
+  // True if we read the timecode scale from the segment info or have
+  // confirmed that the default value is to be used.
+  bool mGotTimecodeScale;
+};
+
+class WebMBufferedState final
+{
+  NS_INLINE_DECL_THREADSAFE_REFCOUNTING(WebMBufferedState)
+
+public:
+  WebMBufferedState()
+    : mReentrantMonitor("WebMBufferedState")
+    , mLastBlockOffset(-1)
+  {
+    MOZ_COUNT_CTOR(WebMBufferedState);
+  }
+
+  void NotifyDataArrived(const unsigned char* aBuffer, uint32_t aLength, int64_t aOffset);
+  void Reset();
+  void UpdateIndex(const MediaByteRangeSet& aRanges, MediaResource* aResource);
+  bool CalculateBufferedForRange(int64_t aStartOffset, int64_t aEndOffset,
+                                 uint64_t* aStartTime, uint64_t* aEndTime);
+
+  // Returns true if mTimeMapping is not empty and sets aOffset to
+  // the latest offset for which decoding can resume without data
+  // dependencies to arrive at aTime. aTime will be clamped to the start
+  // of mTimeMapping if it is earlier than the first element, and to the end
+  // if later than the last
+  bool GetOffsetForTime(uint64_t aTime, int64_t* aOffset);
+
+  // Returns end offset of init segment or -1 if none found.
+  int64_t GetInitEndOffset();
+  // Returns the end offset of the last complete block or -1 if none found.
+  int64_t GetLastBlockOffset();
+
+  // Returns start time
+  bool GetStartTime(uint64_t *aTime);
+
+  // Returns keyframe for time
+  bool GetNextKeyframeTime(uint64_t aTime, uint64_t* aKeyframeTime);
+
+private:
+  // Private destructor, to discourage deletion outside of Release():
+  ~WebMBufferedState() {
+    MOZ_COUNT_DTOR(WebMBufferedState);
+  }
+
+  // Synchronizes access to the mTimeMapping array and mLastBlockOffset.
+  ReentrantMonitor mReentrantMonitor;
+
+  // Sorted (by offset) map of data offsets to timecodes.  Populated
+  // on the main thread as data is received and parsed by WebMBufferedParsers.
+  nsTArray<WebMTimeDataOffset> mTimeMapping;
+  // The last complete block parsed. -1 if not set.
+  int64_t mLastBlockOffset;
+
+  // Sorted (by offset) live parser instances.  Main thread only.
+  nsTArray<WebMBufferedParser> mRangeParsers;
+};
+
+} // namespace mozilla
+
+#endif