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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 */
#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),
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),
mGotClusterTimecode(false) {
if (mStartOffset != 0) {
uint32_t GetTimecodeScale() {
return mTimecodeScale;
// Use this function when we would only feed media segment for the parser.
void AppendMediaSegmentOnly() { mGotTimecodeScale = true; }
// 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);
// Return the Cluster offset, return -1 if we can't find the Cluster.
int64_t GetClusterOffset() const;
// 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;
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.
// Store element ID read into mVInt into mElement.mID. Move to
// READ_VINT with mVIntRaw false, then return to PARSE_ELEMENT.
// Parser start state for parsers started at an arbitrary offset. Scans
// forward for the first cluster, then move to READ_ELEMENT_ID.
// 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.
// 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.
// Reads the remaining mVIntLeft bytes into mVInt.mValue.
// mVInt holds the parsed timecode scale, store it in mTimecodeScale,
// then return READ_ELEMENT_ID.
// mVInt holds the parsed cluster timecode, store it in
// mClusterTimecode, then return to READ_ELEMENT_ID.
// 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.
// 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.
// Skip mSkipBytes of data before resuming parse at mNextState.
// 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. -1 if unknown.
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;
// True if we've read the cluster time code.
bool mGotClusterTimecode;
class WebMBufferedState final {
: mReentrantMonitor("WebMBufferedState"), mLastBlockOffset(-1) {
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 destructor, to discourage deletion outside of Release():
// 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