Source code
Revision control
Copy as Markdown
Other Tools
/* -*- 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
#include "WebMBufferedParser.h"
#include <algorithm>
#include "mozilla/CheckedInt.h"
#include "nsAlgorithm.h"
#include "nsThreadUtils.h"
extern mozilla::LazyLogModule gMediaDemuxerLog;
#define WEBM_DEBUG(arg, ...) \
MOZ_LOG(gMediaDemuxerLog, mozilla::LogLevel::Debug, \
("WebMBufferedParser(%p)::%s: " arg, this, __func__, ##__VA_ARGS__))
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;
}
constexpr uint8_t EBML_MAX_ID_LENGTH_DEFAULT = 4;
constexpr uint8_t EBML_MAX_SIZE_LENGTH_DEFAULT = 8;
WebMBufferedParser::WebMBufferedParser(int64_t aOffset)
: mStartOffset(aOffset),
mCurrentOffset(aOffset),
mInitEndOffset(-1),
mBlockEndOffset(-1),
mState(READ_ELEMENT_ID),
mNextState(READ_ELEMENT_ID),
mVIntRaw(false),
mLastInitStartOffset(-1),
mLastInitSize(0),
mEBMLMaxIdLength(EBML_MAX_ID_LENGTH_DEFAULT),
mEBMLMaxSizeLength(EBML_MAX_SIZE_LENGTH_DEFAULT),
mClusterSyncPos(0),
mVIntLeft(0),
mBlockSize(0),
mClusterTimecode(0),
mClusterOffset(-1),
mClusterEndOffset(-1),
mBlockOffset(0),
mBlockTimecode(0),
mBlockTimecodeLength(0),
mSkipBytes(0),
mTimecodeScale(1000000),
mGotTimecodeScale(false),
mGotClusterTimecode(false) {
if (mStartOffset != 0) {
mState = FIND_CLUSTER_SYNC;
}
}
MediaResult WebMBufferedParser::Append(const unsigned char* aBuffer,
uint32_t aLength,
nsTArray<WebMTimeDataOffset>& aMapping) {
static const uint32_t EBML_ID = 0x1a45dfa3;
static const uint32_t SEGMENT_ID = 0x18538067;
static const uint32_t SEGINFO_ID = 0x1549a966;
static const uint32_t TRACKS_ID = 0x1654AE6B;
static const uint32_t CLUSTER_ID = 0x1f43b675;
static const uint32_t TIMECODESCALE_ID = 0x2ad7b1;
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;
static const uint16_t EBML_MAX_ID_LENGTH_ID = 0x42f2;
static const uint16_t EBML_MAX_SIZE_LENGTH_ID = 0x42f3;
static const uint32_t BLOCK_TIMECODE_LENGTH = 2;
static const unsigned char CLUSTER_SYNC_ID[] = {0x1f, 0x43, 0xb6, 0x75};
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 READ_ELEMENT_ID:
mVIntRaw = true;
mState = READ_VINT;
mNextState = READ_ELEMENT_SIZE;
break;
case READ_ELEMENT_SIZE:
if (mVInt.mLength > mEBMLMaxIdLength) {
nsPrintfCString detail("Invalid element id of length %" PRIu64,
mVInt.mLength);
WEBM_DEBUG("%s", detail.get());
return MediaResult(NS_ERROR_FAILURE, detail);
}
mVIntRaw = false;
mElement.mID = mVInt;
mState = READ_VINT;
mNextState = PARSE_ELEMENT;
break;
case FIND_CLUSTER_SYNC:
if (*p++ == CLUSTER_SYNC_ID[mClusterSyncPos]) {
mClusterSyncPos += 1;
} else {
mClusterSyncPos = 0;
}
if (mClusterSyncPos == sizeof(CLUSTER_SYNC_ID)) {
mVInt.mValue = CLUSTER_ID;
mVInt.mLength = sizeof(CLUSTER_SYNC_ID);
mState = READ_ELEMENT_SIZE;
}
break;
case PARSE_ELEMENT:
if (mVInt.mLength > mEBMLMaxSizeLength) {
nsPrintfCString detail("Invalid element size of length %" PRIu64,
mVInt.mLength);
WEBM_DEBUG("%s", detail.get());
return MediaResult(NS_ERROR_FAILURE, detail);
}
mElement.mSize = mVInt;
switch (mElement.mID.mValue) {
case SEGMENT_ID:
mState = READ_ELEMENT_ID;
break;
case SEGINFO_ID:
mGotTimecodeScale = true;
mState = READ_ELEMENT_ID;
break;
case TIMECODE_ID:
mVInt = VInt();
mVIntLeft = mElement.mSize.mValue;
mState = READ_VINT_REST;
mNextState = READ_CLUSTER_TIMECODE;
break;
case TIMECODESCALE_ID:
mVInt = VInt();
mVIntLeft = mElement.mSize.mValue;
mState = READ_VINT_REST;
mNextState = READ_TIMECODESCALE;
break;
case CLUSTER_ID:
mClusterOffset = mCurrentOffset + (p - aBuffer) -
(mElement.mID.mLength + mElement.mSize.mLength);
// Handle "unknown" length;
if (mElement.mSize.mValue + 1 !=
uint64_t(1) << (mElement.mSize.mLength * 7)) {
mClusterEndOffset = mClusterOffset + mElement.mID.mLength +
mElement.mSize.mLength +
mElement.mSize.mValue;
} else {
mClusterEndOffset = -1;
}
mGotClusterTimecode = false;
mState = READ_ELEMENT_ID;
break;
case BLOCKGROUP_ID:
mState = READ_ELEMENT_ID;
break;
case SIMPLEBLOCK_ID:
/* FALLTHROUGH */
case BLOCK_ID:
if (!mGotClusterTimecode) {
WEBM_DEBUG(
"The Timecode element must appear before any Block or "
"SimpleBlock elements in a Cluster");
return MediaResult(
NS_ERROR_FAILURE,
"The Timecode element must appear before any Block or "
"SimpleBlock elements in a Cluster");
}
mBlockSize = mElement.mSize.mValue;
mBlockTimecode = 0;
mBlockTimecodeLength = BLOCK_TIMECODE_LENGTH;
mBlockOffset = mCurrentOffset + (p - aBuffer) -
(mElement.mID.mLength + mElement.mSize.mLength);
mState = READ_VINT;
mNextState = READ_BLOCK_TIMECODE;
break;
case TRACKS_ID:
mSkipBytes = mElement.mSize.mValue;
mState = CHECK_INIT_FOUND;
break;
case EBML_MAX_ID_LENGTH_ID:
case EBML_MAX_SIZE_LENGTH_ID:
if (int64_t currentOffset = mCurrentOffset + (p - aBuffer);
currentOffset < mLastInitStartOffset ||
currentOffset >= mLastInitStartOffset + mLastInitSize) {
nsPrintfCString str("Unexpected %s outside init segment",
mElement.mID.mValue == EBML_MAX_ID_LENGTH_ID
? "EBMLMaxIdLength"
: "EBMLMaxSizeLength");
WEBM_DEBUG("%s", str.get());
return MediaResult(NS_ERROR_FAILURE, str);
}
if (mElement.mSize.mValue > 8) {
// An Unsigned Integer Element MUST declare a length from zero
// to eight octets.
nsPrintfCString str("Bad length of %s size",
mElement.mID.mValue == EBML_MAX_ID_LENGTH_ID
? "EBMLMaxIdLength"
: "EBMLMaxSizeLength");
WEBM_DEBUG("%s", str.get());
return MediaResult(NS_ERROR_FAILURE, str);
}
mVInt = VInt();
mVIntLeft = mElement.mSize.mValue;
mState = READ_VINT_REST;
mNextState = mElement.mID.mValue == EBML_MAX_ID_LENGTH_ID
? READ_EBML_MAX_ID_LENGTH
: READ_EBML_MAX_SIZE_LENGTH;
break;
case EBML_ID:
mLastInitStartOffset =
mCurrentOffset + (p - aBuffer) -
(mElement.mID.mLength + mElement.mSize.mLength);
mLastInitSize = mElement.mSize.mValue;
mEBMLMaxIdLength = EBML_MAX_ID_LENGTH_DEFAULT;
mEBMLMaxSizeLength = EBML_MAX_SIZE_LENGTH_DEFAULT;
mState = READ_ELEMENT_ID;
break;
default:
mSkipBytes = mElement.mSize.mValue;
mState = SKIP_DATA;
mNextState = READ_ELEMENT_ID;
break;
}
break;
case READ_VINT: {
unsigned char c = *p++;
uint32_t mask;
mVInt.mLength = VIntLength(c, &mask);
mVIntLeft = mVInt.mLength - 1;
mVInt.mValue = mVIntRaw ? c : c & ~mask;
mState = READ_VINT_REST;
break;
}
case READ_VINT_REST:
if (mVIntLeft) {
mVInt.mValue <<= 8;
mVInt.mValue |= *p++;
mVIntLeft -= 1;
} else {
mState = mNextState;
}
break;
case READ_TIMECODESCALE:
if (!mGotTimecodeScale) {
WEBM_DEBUG("Should get the SegmentInfo first");
return MediaResult(NS_ERROR_FAILURE,
"TimecodeScale appeared before SegmentInfo");
}
mTimecodeScale = mVInt.mValue;
mState = READ_ELEMENT_ID;
break;
case READ_CLUSTER_TIMECODE:
mClusterTimecode = mVInt.mValue;
mGotClusterTimecode = true;
mState = READ_ELEMENT_ID;
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.
{
int64_t endOffset = mBlockOffset + mBlockSize +
mElement.mID.mLength + mElement.mSize.mLength;
uint32_t idx = aMapping.IndexOfFirstElementGt(endOffset);
if (idx == 0 || aMapping[idx - 1] != endOffset) {
// Don't insert invalid negative timecodes.
if (mBlockTimecode >= 0 ||
mClusterTimecode >= uint16_t(abs(mBlockTimecode))) {
if (!mGotTimecodeScale) {
WEBM_DEBUG("Should get the TimecodeScale first");
return MediaResult(NS_ERROR_FAILURE,
"Timecode appeared before SegmentInfo");
}
uint64_t absTimecode = mClusterTimecode + mBlockTimecode;
absTimecode *= mTimecodeScale;
// Avoid creating an entry if the timecode is out of order
// (invalid according to the WebM specification) so that
// ordering invariants of aMapping are not violated.
if (idx == 0 || aMapping[idx - 1].mTimecode <= absTimecode ||
(idx + 1 < aMapping.Length() &&
aMapping[idx + 1].mTimecode >= absTimecode)) {
WebMTimeDataOffset entry(endOffset, absTimecode,
mLastInitStartOffset, mClusterOffset,
mClusterEndOffset);
aMapping.InsertElementAt(idx, entry);
} else {
WEBM_DEBUG("Out of order timecode %" PRIu64
" in Cluster at %" PRId64 " ignored",
absTimecode, mClusterOffset);
}
}
}
}
// Skip rest of block header and the block's payload.
mBlockSize -= mVInt.mLength;
mBlockSize -= BLOCK_TIMECODE_LENGTH;
mSkipBytes = uint32_t(mBlockSize);
mState = SKIP_DATA;
mNextState = READ_ELEMENT_ID;
}
break;
case READ_EBML_MAX_ID_LENGTH:
if (mElement.mSize.mLength == 0) {
// If an Empty Element has a default value declared, then the EBML
// Reader MUST interpret the value of the Empty Element as the
// default value.
mVInt.mValue = EBML_MAX_ID_LENGTH_DEFAULT;
}
if (mVInt.mValue < 4 || mVInt.mValue > 5) {
// (Matroska):
// The EBMLMaxIDLength of the EBML Header MUST be "4".
//
// Also Matroska:
// Element IDs are encoded using the VINT mechanism described in
// Section 4 of [RFC8794] and can be between one and five octets
// long. Five-octet-long Element IDs are possible only if declared
// in the EBML header.
nsPrintfCString detail("Invalid EMBLMaxIdLength %" PRIu64,
mVInt.mValue);
WEBM_DEBUG("%s", detail.get());
return MediaResult(NS_ERROR_FAILURE, detail);
}
mEBMLMaxIdLength = mVInt.mValue;
mState = READ_ELEMENT_ID;
break;
case READ_EBML_MAX_SIZE_LENGTH:
if (mElement.mSize.mLength == 0) {
// If an Empty Element has a default value declared, then the EBML
// Reader MUST interpret the value of the Empty Element as the
// default value.
mVInt.mValue = EBML_MAX_SIZE_LENGTH_DEFAULT;
}
if (mVInt.mValue < 1 || mVInt.mValue > 8) {
// (Matroska):
// The EBMLMaxSizeLength of the EBML Header MUST be between "1" and
// "8" inclusive.
nsPrintfCString detail("Invalid EMBLMaxSizeLength %" PRIu64,
mVInt.mValue);
WEBM_DEBUG("%s", detail.get());
return MediaResult(NS_ERROR_FAILURE, detail);
}
mEBMLMaxSizeLength = mVInt.mValue;
mState = READ_ELEMENT_ID;
break;
case SKIP_DATA:
if (mSkipBytes) {
uint32_t left = aLength - (p - aBuffer);
left = std::min(left, mSkipBytes);
p += left;
mSkipBytes -= left;
}
if (!mSkipBytes) {
mBlockEndOffset = mCurrentOffset + (p - aBuffer);
mState = mNextState;
}
break;
case CHECK_INIT_FOUND:
if (mSkipBytes) {
uint32_t left = aLength - (p - aBuffer);
left = std::min(left, mSkipBytes);
p += left;
mSkipBytes -= left;
}
if (!mSkipBytes) {
if (mInitEndOffset < 0) {
mInitEndOffset = mCurrentOffset + (p - aBuffer);
mBlockEndOffset = mCurrentOffset + (p - aBuffer);
}
mState = READ_ELEMENT_ID;
}
break;
}
}
NS_ASSERTION(p == aBuffer + aLength, "Must have parsed to end of data.");
mCurrentOffset += aLength;
return NS_OK;
}
int64_t WebMBufferedParser::EndSegmentOffset(int64_t aOffset) {
if (mLastInitStartOffset > aOffset || mClusterOffset > aOffset) {
return std::min(
mLastInitStartOffset >= 0 ? mLastInitStartOffset : INT64_MAX,
mClusterOffset >= 0 ? mClusterOffset : INT64_MAX);
}
return mBlockEndOffset;
}
int64_t WebMBufferedParser::GetClusterOffset() const { return mClusterOffset; }
// SyncOffsetComparator and TimeComparator are slightly confusing, in that
// the nsTArray they're used with (mTimeMapping) is sorted by mEndOffset and
// these comparators are used on the other fields of WebMTimeDataOffset.
// This is only valid because timecodes are required to be monotonically
// increasing within a file (thus establishing an ordering relationship with
// mTimecode), and mEndOffset is derived from mSyncOffset.
struct SyncOffsetComparator {
bool Equals(const WebMTimeDataOffset& a, const int64_t& b) const {
return a.mSyncOffset == b;
}
bool LessThan(const WebMTimeDataOffset& a, const int64_t& b) const {
return a.mSyncOffset < b;
}
};
struct TimeComparator {
bool Equals(const WebMTimeDataOffset& a, const uint64_t& b) const {
return a.mTimecode == b;
}
bool LessThan(const WebMTimeDataOffset& a, const uint64_t& b) const {
return a.mTimecode < b;
}
};
bool WebMBufferedState::CalculateBufferedForRange(int64_t aStartOffset,
int64_t aEndOffset,
uint64_t* aStartTime,
uint64_t* aEndTime) {
MutexAutoLock lock(mMutex);
// Find the first WebMTimeDataOffset at or after aStartOffset.
uint32_t start = mTimeMapping.IndexOfFirstElementGt(aStartOffset - 1,
SyncOffsetComparator());
if (start == mTimeMapping.Length()) {
return false;
}
// Find the first WebMTimeDataOffset at or before aEndOffset.
uint32_t end = mTimeMapping.IndexOfFirstElementGt(aEndOffset);
if (end > 0) {
end -= 1;
}
// Range is empty.
if (end <= start) {
return false;
}
NS_ASSERTION(mTimeMapping[start].mSyncOffset >= aStartOffset &&
mTimeMapping[end].mEndOffset <= aEndOffset,
"Computed time range must lie within data range.");
if (start > 0) {
NS_ASSERTION(mTimeMapping[start - 1].mSyncOffset < aStartOffset,
"Must have found least WebMTimeDataOffset for start");
}
if (end < mTimeMapping.Length() - 1) {
NS_ASSERTION(mTimeMapping[end + 1].mEndOffset > aEndOffset,
"Must have found greatest WebMTimeDataOffset for end");
}
MOZ_ASSERT(mTimeMapping[end].mTimecode >= mTimeMapping[end - 1].mTimecode);
uint64_t frameDuration =
mTimeMapping[end].mTimecode - mTimeMapping[end - 1].mTimecode;
*aStartTime = mTimeMapping[start].mTimecode;
CheckedUint64 endTime{mTimeMapping[end].mTimecode};
endTime += frameDuration;
if (!endTime.isValid()) {
WEBM_DEBUG("End time overflow during CalculateBufferedForRange.");
return false;
}
*aEndTime = endTime.value();
return true;
}
bool WebMBufferedState::GetOffsetForTime(uint64_t aTime, int64_t* aOffset) {
MutexAutoLock lock(mMutex);
if (mTimeMapping.IsEmpty()) {
return false;
}
uint64_t time = aTime;
if (time > 0) {
time = time - 1;
}
uint32_t idx = mTimeMapping.IndexOfFirstElementGt(time, TimeComparator());
if (idx == mTimeMapping.Length()) {
// Clamp to end
*aOffset = mTimeMapping[mTimeMapping.Length() - 1].mSyncOffset;
} else {
// Idx is within array or has been clamped to start
*aOffset = mTimeMapping[idx].mSyncOffset;
}
return true;
}
void WebMBufferedState::NotifyDataArrived(const unsigned char* aBuffer,
uint32_t aLength, int64_t aOffset) {
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));
if (idx != 0) {
mRangeParsers[idx].SetTimecodeScale(
mRangeParsers[0].GetTimecodeScale());
}
}
}
{
MutexAutoLock lock(mMutex);
mRangeParsers[idx].Append(aBuffer, aLength, mTimeMapping);
}
// 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[i + 1].mInitEndOffset = mRangeParsers[i].mInitEndOffset;
mRangeParsers.RemoveElementAt(i);
} else {
i += 1;
}
}
if (mRangeParsers.IsEmpty()) {
return;
}
MutexAutoLock lock(mMutex);
mLastBlockOffset = mRangeParsers.LastElement().mBlockEndOffset;
}
void WebMBufferedState::Reset() {
MutexAutoLock lock(mMutex);
mRangeParsers.Clear();
mTimeMapping.Clear();
}
void WebMBufferedState::UpdateIndex(const MediaByteRangeSet& aRanges,
MediaResource* aResource) {
for (uint32_t index = 0; index < aRanges.Length(); index++) {
const MediaByteRange& range = aRanges[index];
int64_t offset = range.mStart;
uint32_t length = range.mEnd - range.mStart;
uint32_t idx = mRangeParsers.IndexOfFirstElementGt(offset - 1);
if (!idx || !(mRangeParsers[idx - 1] == offset)) {
// 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 <= offset) {
// Complete overlap, skip parsing.
if (offset + length <= mRangeParsers[idx].mCurrentOffset) {
continue;
}
// Partial overlap, adjust the buffer to parse only the new data.
int64_t adjust = mRangeParsers[idx].mCurrentOffset - offset;
NS_ASSERTION(adjust >= 0, "Overlap detection bug.");
offset += adjust;
length -= uint32_t(adjust);
} else {
mRangeParsers.InsertElementAt(idx, WebMBufferedParser(offset));
if (idx) {
mRangeParsers[idx].SetTimecodeScale(
mRangeParsers[0].GetTimecodeScale());
}
}
}
MediaResourceIndex res(aResource);
while (length > 0) {
static const uint32_t BLOCK_SIZE = 1048576;
uint32_t block = std::min(length, BLOCK_SIZE);
RefPtr<MediaByteBuffer> bytes = res.CachedMediaReadAt(offset, block);
if (!bytes) {
break;
}
NotifyDataArrived(bytes->Elements(), bytes->Length(), offset);
length -= bytes->Length();
offset += bytes->Length();
}
}
}
int64_t WebMBufferedState::GetInitEndOffset() {
if (mRangeParsers.IsEmpty()) {
return -1;
}
return mRangeParsers[0].mInitEndOffset;
}
int64_t WebMBufferedState::GetLastBlockOffset() {
MutexAutoLock lock(mMutex);
return mLastBlockOffset;
}
bool WebMBufferedState::GetStartTime(uint64_t* aTime) {
MutexAutoLock lock(mMutex);
if (mTimeMapping.IsEmpty()) {
return false;
}
uint32_t idx = mTimeMapping.IndexOfFirstElementGt(0, SyncOffsetComparator());
if (idx == mTimeMapping.Length()) {
return false;
}
*aTime = mTimeMapping[idx].mTimecode;
return true;
}
bool WebMBufferedState::GetNextKeyframeTime(uint64_t aTime,
uint64_t* aKeyframeTime) {
MutexAutoLock lock(mMutex);
int64_t offset = 0;
bool rv = GetOffsetForTime(aTime, &offset);
if (!rv) {
return false;
}
uint32_t idx =
mTimeMapping.IndexOfFirstElementGt(offset, SyncOffsetComparator());
if (idx == mTimeMapping.Length()) {
return false;
}
*aKeyframeTime = mTimeMapping[idx].mTimecode;
return true;
}
} // namespace mozilla
#undef WEBM_DEBUG