gecko-dev/content/media/webm/WebMBufferedParser.cpp

283 lines
8.8 KiB
C++

/* -*- 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 "nsAlgorithm.h"
#include "WebMBufferedParser.h"
#include "mozilla/dom/TimeRanges.h"
#include "nsThreadUtils.h"
#include <algorithm>
namespace mozilla {
static uint32_t
VIntLength(unsigned char aFirstByte, uint32_t* aMask)
{
uint32_t count = 1;
uint32_t mask = 1 << 7;
while (count < 8) {
if ((aFirstByte & mask) != 0) {
break;
}
mask >>= 1;
count += 1;
}
if (aMask) {
*aMask = mask;
}
NS_ASSERTION(count >= 1 && count <= 8, "Insane VInt length.");
return count;
}
void WebMBufferedParser::Append(const unsigned char* aBuffer, uint32_t aLength,
nsTArray<WebMTimeDataOffset>& aMapping,
ReentrantMonitor& aReentrantMonitor)
{
static const unsigned char CLUSTER_ID[] = { 0x1f, 0x43, 0xb6, 0x75 };
static const unsigned char TIMECODE_ID = 0xe7;
static const unsigned char BLOCKGROUP_ID = 0xa0;
static const unsigned char BLOCK_ID = 0xa1;
static const unsigned char SIMPLEBLOCK_ID = 0xa3;
const unsigned char* p = aBuffer;
// Parse each byte in aBuffer one-by-one, producing timecodes and updating
// aMapping as we go. Parser pauses at end of stream (which may be at any
// point within the parse) and resumes parsing the next time Append is
// called with new data.
while (p < aBuffer + aLength) {
switch (mState) {
case CLUSTER_SYNC:
if (*p++ == CLUSTER_ID[mClusterIDPos]) {
mClusterIDPos += 1;
} else {
mClusterIDPos = 0;
}
// Cluster ID found, it's likely this is a valid sync point. If this
// is a spurious match, the later parse steps will encounter an error
// and return to CLUSTER_SYNC.
if (mClusterIDPos == sizeof(CLUSTER_ID)) {
mClusterIDPos = 0;
mState = READ_VINT;
mNextState = TIMECODE_SYNC;
}
break;
case READ_VINT: {
unsigned char c = *p++;
uint32_t mask;
mVIntLength = VIntLength(c, &mask);
mVIntLeft = mVIntLength - 1;
mVInt = c & ~mask;
mState = READ_VINT_REST;
break;
}
case READ_VINT_REST:
if (mVIntLeft) {
mVInt <<= 8;
mVInt |= *p++;
mVIntLeft -= 1;
} else {
mState = mNextState;
}
break;
case TIMECODE_SYNC:
if (*p++ != TIMECODE_ID) {
p -= 1;
mState = CLUSTER_SYNC;
break;
}
mClusterTimecode = 0;
mState = READ_VINT;
mNextState = READ_CLUSTER_TIMECODE;
break;
case READ_CLUSTER_TIMECODE:
if (mVInt) {
mClusterTimecode <<= 8;
mClusterTimecode |= *p++;
mVInt -= 1;
} else {
mState = ANY_BLOCK_SYNC;
}
break;
case ANY_BLOCK_SYNC: {
unsigned char c = *p++;
if (c == BLOCKGROUP_ID) {
mState = READ_VINT;
mNextState = ANY_BLOCK_SYNC;
} else if (c == SIMPLEBLOCK_ID || c == BLOCK_ID) {
mBlockOffset = mCurrentOffset + (p - aBuffer) - 1;
mState = READ_VINT;
mNextState = READ_BLOCK;
} else {
uint32_t length = VIntLength(c, nullptr);
if (length == 4) {
p -= 1;
mState = CLUSTER_SYNC;
} else {
mState = READ_VINT;
mNextState = SKIP_ELEMENT;
}
}
break;
}
case READ_BLOCK:
mBlockSize = mVInt;
mBlockTimecode = 0;
mBlockTimecodeLength = 2;
mState = READ_VINT;
mNextState = READ_BLOCK_TIMECODE;
break;
case READ_BLOCK_TIMECODE:
if (mBlockTimecodeLength) {
mBlockTimecode <<= 8;
mBlockTimecode |= *p++;
mBlockTimecodeLength -= 1;
} else {
// It's possible we've parsed this data before, so avoid inserting
// duplicate WebMTimeDataOffset entries.
{
ReentrantMonitorAutoEnter mon(aReentrantMonitor);
uint32_t idx = aMapping.IndexOfFirstElementGt(mBlockOffset);
if (idx == 0 || !(aMapping[idx-1] == mBlockOffset)) {
WebMTimeDataOffset entry(mBlockOffset, mClusterTimecode + mBlockTimecode);
aMapping.InsertElementAt(idx, entry);
}
}
// Skip rest of block header and the block's payload.
mBlockSize -= mVIntLength;
mBlockSize -= 2;
mSkipBytes = uint32_t(mBlockSize);
mState = SKIP_DATA;
mNextState = ANY_BLOCK_SYNC;
}
break;
case SKIP_DATA:
if (mSkipBytes) {
uint32_t left = aLength - (p - aBuffer);
left = std::min(left, mSkipBytes);
p += left;
mSkipBytes -= left;
} else {
mState = mNextState;
}
break;
case SKIP_ELEMENT:
mSkipBytes = uint32_t(mVInt);
mState = SKIP_DATA;
mNextState = ANY_BLOCK_SYNC;
break;
}
}
NS_ASSERTION(p == aBuffer + aLength, "Must have parsed to end of data.");
mCurrentOffset += aLength;
}
bool WebMBufferedState::CalculateBufferedForRange(int64_t aStartOffset, int64_t aEndOffset,
uint64_t* aStartTime, uint64_t* aEndTime)
{
ReentrantMonitorAutoEnter mon(mReentrantMonitor);
// Find the first WebMTimeDataOffset at or after aStartOffset.
uint32_t start = mTimeMapping.IndexOfFirstElementGt(aStartOffset-1);
if (start == mTimeMapping.Length()) {
return false;
}
// Find the first WebMTimeDataOffset at or before aEndOffset.
uint32_t end = mTimeMapping.IndexOfFirstElementGt(aEndOffset-1);
if (end > 0) {
end -= 1;
}
// Range is empty.
if (end <= start) {
return false;
}
NS_ASSERTION(mTimeMapping[start].mOffset >= aStartOffset &&
mTimeMapping[end].mOffset <= aEndOffset,
"Computed time range must lie within data range.");
if (start > 0) {
NS_ASSERTION(mTimeMapping[start - 1].mOffset <= aStartOffset,
"Must have found least WebMTimeDataOffset for start");
}
if (end < mTimeMapping.Length() - 1) {
NS_ASSERTION(mTimeMapping[end + 1].mOffset >= aEndOffset,
"Must have found greatest WebMTimeDataOffset for end");
}
// The timestamp of the first media sample, in ns. We must subtract this
// from the ranges' start and end timestamps, so that those timestamps are
// normalized in the range [0,duration].
*aStartTime = mTimeMapping[start].mTimecode;
*aEndTime = mTimeMapping[end].mTimecode;
return true;
}
bool WebMBufferedState::GetOffsetForTime(uint64_t aTime, int64_t* aOffset)
{
ReentrantMonitorAutoEnter mon(mReentrantMonitor);
WebMTimeDataOffset result(0,0);
for (uint32_t i = 0; i < mTimeMapping.Length(); ++i) {
WebMTimeDataOffset o = mTimeMapping[i];
if (o.mTimecode < aTime && o.mTimecode > result.mTimecode) {
result = o;
}
}
*aOffset = result.mOffset;
return true;
}
void WebMBufferedState::NotifyDataArrived(const char* aBuffer, uint32_t aLength, int64_t aOffset)
{
NS_ASSERTION(NS_IsMainThread(), "Should be on main thread.");
uint32_t idx = mRangeParsers.IndexOfFirstElementGt(aOffset - 1);
if (idx == 0 || !(mRangeParsers[idx-1] == aOffset)) {
// If the incoming data overlaps an already parsed range, adjust the
// buffer so that we only reparse the new data. It's also possible to
// have an overlap where the end of the incoming data is within an
// already parsed range, but we don't bother handling that other than by
// avoiding storing duplicate timecodes when the parser runs.
if (idx != mRangeParsers.Length() && mRangeParsers[idx].mStartOffset <= aOffset) {
// Complete overlap, skip parsing.
if (aOffset + aLength <= mRangeParsers[idx].mCurrentOffset) {
return;
}
// Partial overlap, adjust the buffer to parse only the new data.
int64_t adjust = mRangeParsers[idx].mCurrentOffset - aOffset;
NS_ASSERTION(adjust >= 0, "Overlap detection bug.");
aBuffer += adjust;
aLength -= uint32_t(adjust);
} else {
mRangeParsers.InsertElementAt(idx, WebMBufferedParser(aOffset));
}
}
mRangeParsers[idx].Append(reinterpret_cast<const unsigned char*>(aBuffer),
aLength,
mTimeMapping,
mReentrantMonitor);
// Merge parsers with overlapping regions and clean up the remnants.
uint32_t i = 0;
while (i + 1 < mRangeParsers.Length()) {
if (mRangeParsers[i].mCurrentOffset >= mRangeParsers[i + 1].mStartOffset) {
mRangeParsers[i + 1].mStartOffset = mRangeParsers[i].mStartOffset;
mRangeParsers.RemoveElementAt(i);
} else {
i += 1;
}
}
}
} // namespace mozilla