gecko/content/media/webm/nsWebMBufferedParser.cpp

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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: */
/* ***** BEGIN LICENSE BLOCK *****
* Version: MPL 1.1/GPL 2.0/LGPL 2.1
*
* The contents of this file are subject to the Mozilla Public License Version
* 1.1 (the "License"); you may not use this file except in compliance with
* the License. You may obtain a copy of the License at
* http://www.mozilla.org/MPL/
*
* Software distributed under the License is distributed on an "AS IS" basis,
* WITHOUT WARRANTY OF ANY KIND, either express or implied. See the License
* for the specific language governing rights and limitations under the
* License.
*
* The Original Code is Mozilla code.
*
* The Initial Developer of the Original Code is the Mozilla Corporation.
* Portions created by the Initial Developer are Copyright (C) 2010
* the Initial Developer. All Rights Reserved.
*
* Contributor(s):
* Matthew Gregan <kinetik@flim.org>
*
* Alternatively, the contents of this file may be used under the terms of
* either the GNU General Public License Version 2 or later (the "GPL"), or
* the GNU Lesser General Public License Version 2.1 or later (the "LGPL"),
* in which case the provisions of the GPL or the LGPL are applicable instead
* of those above. If you wish to allow use of your version of this file only
* under the terms of either the GPL or the LGPL, and not to allow others to
* use your version of this file under the terms of the MPL, indicate your
* decision by deleting the provisions above and replace them with the notice
* and other provisions required by the GPL or the LGPL. If you do not delete
* the provisions above, a recipient may use your version of this file under
* the terms of any one of the MPL, the GPL or the LGPL.
*
* ***** END LICENSE BLOCK ***** */
#include "nsAlgorithm.h"
#include "nsWebMBufferedParser.h"
static PRUint32
VIntLength(unsigned char aFirstByte, PRUint32* aMask)
{
PRUint32 count = 1;
PRUint32 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 nsWebMBufferedParser::Append(const unsigned char* aBuffer, PRUint32 aLength,
nsTArray<nsWebMTimeDataOffset>& aMapping)
{
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++;
PRUint32 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 {
PRUint32 length = VIntLength(c, nsnull);
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 nsWebMTimeDataOffset entries.
PRUint32 idx;
if (!aMapping.GreatestIndexLtEq(mBlockOffset, idx)) {
nsWebMTimeDataOffset entry(mBlockOffset, mClusterTimecode + mBlockTimecode);
aMapping.InsertElementAt(idx, entry);
}
// Skip rest of block header and the block's payload.
mBlockSize -= mVIntLength;
mBlockSize -= 2;
mSkipBytes = PRUint32(mBlockSize);
mState = SKIP_DATA;
mNextState = ANY_BLOCK_SYNC;
}
break;
case SKIP_DATA:
if (mSkipBytes) {
PRUint32 left = aLength - (p - aBuffer);
left = NS_MIN(left, mSkipBytes);
p += left;
mSkipBytes -= left;
} else {
mState = mNextState;
}
break;
case SKIP_ELEMENT:
mSkipBytes = PRUint32(mVInt);
mState = SKIP_DATA;
mNextState = ANY_BLOCK_SYNC;
break;
}
}
NS_ASSERTION(p == aBuffer + aLength, "Must have parsed to end of data.");
mCurrentOffset += aLength;
}