The Tor Browser: comparison content/media/MP3FrameParser.cpp

--1:000000000000
+:5935149ce3d1
+/* -*- 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 <algorithm>
+#include "nsMemory.h"
+#include "MP3FrameParser.h"
+#include "VideoUtils.h"
+#define FROM_BIG_ENDIAN(X) ((uint32_t)((uint8_t)(X)[0] << 24 | (uint8_t)(X)[1] << 16 | \
+(uint8_t)(X)[2] << 8 | (uint8_t)(X)[3]))
+namespace mozilla {
+/*
+* Following code taken from http://www.hydrogenaudio.org/forums/index.php?showtopic=85125
+* with permission from the author, Nick Wallette <sirnickity@gmail.com>.
+*/
+/* BEGIN shameless copy and paste */
+// Bitrates - use [version][layer][bitrate]
+const uint16_t mpeg_bitrates[4][4][16] = {
+{ // Version 2.5
+{ 0,   0,   0,   0,   0,   0,   0,   0,   0,   0,   0,   0,   0,   0,   0, 0 }, // Reserved
+{ 0,   8,  16,  24,  32,  40,  48,  56,  64,  80,  96, 112, 128, 144, 160, 0 }, // Layer 3
+{ 0,   8,  16,  24,  32,  40,  48,  56,  64,  80,  96, 112, 128, 144, 160, 0 }, // Layer 2
+{ 0,  32,  48,  56,  64,  80,  96, 112, 128, 144, 160, 176, 192, 224, 256, 0 }  // Layer 1
+},
+{ // Reserved
+{ 0,   0,   0,   0,   0,   0,   0,   0,   0,   0,   0,   0,   0,   0,   0, 0 }, // Invalid
+{ 0,   0,   0,   0,   0,   0,   0,   0,   0,   0,   0,   0,   0,   0,   0, 0 }, // Invalid
+{ 0,   0,   0,   0,   0,   0,   0,   0,   0,   0,   0,   0,   0,   0,   0, 0 }, // Invalid
+{ 0,   0,   0,   0,   0,   0,   0,   0,   0,   0,   0,   0,   0,   0,   0, 0 }  // Invalid
+},
+{ // Version 2
+{ 0,   0,   0,   0,   0,   0,   0,   0,   0,   0,   0,   0,   0,   0,   0, 0 }, // Reserved
+{ 0,   8,  16,  24,  32,  40,  48,  56,  64,  80,  96, 112, 128, 144, 160, 0 }, // Layer 3
+{ 0,   8,  16,  24,  32,  40,  48,  56,  64,  80,  96, 112, 128, 144, 160, 0 }, // Layer 2
+{ 0,  32,  48,  56,  64,  80,  96, 112, 128, 144, 160, 176, 192, 224, 256, 0 }  // Layer 1
+},
+{ // Version 1
+{ 0,   0,   0,   0,   0,   0,   0,   0,   0,   0,   0,   0,   0,   0,   0, 0 }, // Reserved
+{ 0,  32,  40,  48,  56,  64,  80,  96, 112, 128, 160, 192, 224, 256, 320, 0 }, // Layer 3
+{ 0,  32,  48,  56,  64,  80,  96, 112, 128, 160, 192, 224, 256, 320, 384, 0 }, // Layer 2
+{ 0,  32,  64,  96, 128, 160, 192, 224, 256, 288, 320, 352, 384, 416, 448, 0 }, // Layer 1
+}
+};
+// Sample rates - use [version][srate]
+const uint16_t mpeg_srates[4][4] = {
+{ 11025, 12000,  8000, 0 }, // MPEG 2.5
+{     0,     0,     0, 0 }, // Reserved
+{ 22050, 24000, 16000, 0 }, // MPEG 2
+{ 44100, 48000, 32000, 0 }  // MPEG 1
+};
+// Samples per frame - use [version][layer]
+const uint16_t mpeg_frame_samples[4][4] = {
+//    Rsvd     3     2     1  < Layer  v Version
+{    0,  576, 1152,  384 }, //       2.5
+{    0,    0,    0,    0 }, //       Reserved
+{    0,  576, 1152,  384 }, //       2
+{    0, 1152, 1152,  384 }  //       1
+};
+// Slot size (MPEG unit of measurement) - use [layer]
+const uint8_t mpeg_slot_size[4] = { 0, 1, 1, 4 }; // Rsvd, 3, 2, 1
+uint16_t
+MP3Frame::CalculateLength()
+{
+// Lookup real values of these fields
+uint32_t  bitrate   = mpeg_bitrates[mVersion][mLayer][mBitrate] * 1000;
+uint32_t  samprate  = mpeg_srates[mVersion][mSampleRate];
+uint16_t  samples   = mpeg_frame_samples[mVersion][mLayer];
+uint8_t   slot_size = mpeg_slot_size[mLayer];
+// In-between calculations
+float     bps       = (float)samples / 8.0;
+float     fsize     = ( (bps * (float)bitrate) / (float)samprate )
++ ( (mPad) ? slot_size : 0 );
+// Frame sizes are truncated integers
+return (uint16_t)fsize;
+}
+/* END shameless copy and paste */
+/** MP3Parser methods **/
+MP3Parser::MP3Parser()
+: mCurrentChar(0)
+{ }
+void
+MP3Parser::Reset()
+{
+mCurrentChar = 0;
+}
+uint16_t
+MP3Parser::ParseFrameLength(uint8_t ch)
+{
+mData.mRaw[mCurrentChar] = ch;
+MP3Frame &frame = mData.mFrame;
+// Validate MP3 header as we read. We can't mistake the start of an MP3 frame
+// for the middle of another frame due to the sync byte at the beginning
+// of the frame.
+// The only valid position for an all-high byte is the sync byte at the
+// beginning of the frame.
+if (ch == 0xff) {
+mCurrentChar = 0;
+}
+// Make sure the current byte is valid in context. If not, reset the parser.
+if (mCurrentChar == 2) {
+if (frame.mBitrate == 0x0f) {
+goto fail;
+}
+} else if (mCurrentChar == 1) {
+if (frame.mSync2 != 0x07
+|| frame.mVersion == 0x01
+|| frame.mLayer == 0x00) {
+goto fail;
+}
+}
+// The only valid character at the beginning of the header is 0xff. Fail if
+// it's different.
+if (mCurrentChar == 0 && frame.mSync1 != 0xff) {
+// Couldn't find the sync byte. Fail.
+return 0;
+}
+mCurrentChar++;
+MOZ_ASSERT(mCurrentChar <= sizeof(MP3Frame));
+// Don't have a full header yet.
+if (mCurrentChar < sizeof(MP3Frame)) {
+return 0;
+}
+// Woo, valid header. Return the length.
+mCurrentChar = 0;
+return frame.CalculateLength();
+fail:
+Reset();
+return 0;
+}
+uint32_t
+MP3Parser::GetSampleRate()
+{
+MP3Frame &frame = mData.mFrame;
+return mpeg_srates[frame.mVersion][frame.mSampleRate];
+}
+uint32_t
+MP3Parser::GetSamplesPerFrame()
+{
+MP3Frame &frame = mData.mFrame;
+return mpeg_frame_samples[frame.mVersion][frame.mLayer];
+}
+/** ID3Parser methods **/
+const char sID3Head[3] = { 'I', 'D', '3' };
+const uint32_t ID3_HEADER_LENGTH = 10;
+ID3Parser::ID3Parser()
+: mCurrentChar(0)
+, mHeaderLength(0)
+{ }
+void
+ID3Parser::Reset()
+{
+mCurrentChar = mHeaderLength = 0;
+}
+bool
+ID3Parser::ParseChar(char ch)
+{
+// First three bytes of an ID3v2 header must match the string "ID3".
+if (mCurrentChar < sizeof(sID3Head) / sizeof(*sID3Head)
+&& ch != sID3Head[mCurrentChar]) {
+goto fail;
+}
+// The last four bytes of the header is a 28-bit unsigned integer with the
+// high bit of each byte unset.
+if (mCurrentChar >= 6 && mCurrentChar < ID3_HEADER_LENGTH) {
+if (ch & 0x80) {
+goto fail;
+} else {
+mHeaderLength <<= 7;
+mHeaderLength |= ch;
+}
+}
+mCurrentChar++;
+return IsParsed();
+fail:
+Reset();
+return false;
+}
+bool
+ID3Parser::IsParsed() const
+{
+return mCurrentChar >= ID3_HEADER_LENGTH;
+}
+uint32_t
+ID3Parser::GetHeaderLength() const
+{
+MOZ_ASSERT(IsParsed(),
+"Queried length of ID3 header before parsing finished.");
+return mHeaderLength;
+}
+/** VBR header helper stuff **/
+// Helper function to find a VBR header in an MP3 frame.
+// Based on information from
+// http://www.codeproject.com/Articles/8295/MPEG-Audio-Frame-Header
+const uint32_t VBRI_TAG = FROM_BIG_ENDIAN("VBRI");
+const uint32_t VBRI_OFFSET = 32 - sizeof(MP3Frame);
+const uint32_t VBRI_FRAME_COUNT_OFFSET = VBRI_OFFSET + 14;
+const uint32_t VBRI_MIN_FRAME_SIZE = VBRI_OFFSET + 26;
+const uint32_t XING_TAG = FROM_BIG_ENDIAN("Xing");
+enum XingFlags {
+XING_HAS_NUM_FRAMES = 0x01,
+XING_HAS_NUM_BYTES = 0x02,
+XING_HAS_TOC = 0x04,
+XING_HAS_VBR_SCALE = 0x08
+};
+static int64_t
+ParseXing(const char *aBuffer)
+{
+uint32_t flags = FROM_BIG_ENDIAN(aBuffer + 4);
+if (!(flags & XING_HAS_NUM_FRAMES)) {
+NS_WARNING("VBR file without frame count. Duration estimation likely to "
+"be totally wrong.");
+return -1;
+}
+int64_t numFrames = -1;
+if (flags & XING_HAS_NUM_FRAMES) {
+numFrames = FROM_BIG_ENDIAN(aBuffer + 8);
+}
+return numFrames;
+}
+static int64_t
+FindNumVBRFrames(const nsAutoCString& aFrame)
+{
+const char *buffer = aFrame.get();
+const char *bufferEnd = aFrame.get() + aFrame.Length();
+// VBRI header is nice and well-defined; let's try to find that first.
+if (aFrame.Length() > VBRI_MIN_FRAME_SIZE &&
+FROM_BIG_ENDIAN(buffer + VBRI_OFFSET) == VBRI_TAG) {
+return FROM_BIG_ENDIAN(buffer + VBRI_FRAME_COUNT_OFFSET);
+}
+// We have to search for the Xing header as its position can change.
+for (; buffer + sizeof(XING_TAG) < bufferEnd; buffer++) {
+if (FROM_BIG_ENDIAN(buffer) == XING_TAG) {
+return ParseXing(buffer);
+}
+}
+return -1;
+}
+/** MP3FrameParser methods **/
+// Some MP3's have large ID3v2 tags, up to 150KB, so we allow lots of
+// skipped bytes to be read, just in case, before we give up and assume
+// we're not parsing an MP3 stream.
+static const uint32_t MAX_SKIPPED_BYTES = 4096;
+// The number of audio samples per MP3 frame. This is constant over all MP3
+// streams. With this constant, the stream's sample rate, and an estimated
+// number of frames in the stream, we can estimate the stream's duration
+// fairly accurately.
+static const uint32_t SAMPLES_PER_FRAME = 1152;
+enum {
+MP3_HEADER_LENGTH   = 4,
+};
+MP3FrameParser::MP3FrameParser(int64_t aLength)
+: mLock("MP3FrameParser.mLock"),
+mTotalID3Size(0),
+mTotalFrameSize(0),
+mFrameCount(0),
+mOffset(0),
+mLength(aLength),
+mMP3Offset(-1),
+mSamplesPerSecond(0),
+mFirstFrameEnd(-1),
+mIsMP3(MAYBE_MP3)
+{ }
+nsresult MP3FrameParser::ParseBuffer(const uint8_t* aBuffer,
+uint32_t aLength,
+int64_t aStreamOffset,
+uint32_t* aOutBytesRead)
+{
+// Iterate forwards over the buffer, looking for ID3 tag, or MP3
+// Frame headers.
+const uint8_t *buffer = aBuffer;
+const uint8_t *bufferEnd = aBuffer + aLength;
+// If we haven't found any MP3 frame data yet, there might be ID3 headers
+// we can skip over.
+if (mMP3Offset < 0) {
+for (const uint8_t *ch = buffer; ch < bufferEnd; ch++) {
+if (mID3Parser.ParseChar(*ch)) {
+// Found an ID3 header. We don't care about the body of the header, so
+// just skip past.
+buffer = ch + mID3Parser.GetHeaderLength() - (ID3_HEADER_LENGTH - 1);
+ch = buffer;
+mTotalID3Size += mID3Parser.GetHeaderLength();
+// Yes, this is an MP3!
+mIsMP3 = DEFINITELY_MP3;
+mID3Parser.Reset();
+}
+}
+}
+// The first MP3 frame in a variable bitrate stream can contain metadata
+// for duration estimation and seeking, so we buffer that first frame here.
+if (aStreamOffset < mFirstFrameEnd) {
+uint64_t copyLen = std::min((int64_t)aLength, mFirstFrameEnd - aStreamOffset);
+mFirstFrame.Append((const char *)buffer, copyLen);
+buffer += copyLen;
+}
+while (buffer < bufferEnd) {
+uint16_t frameLen = mMP3Parser.ParseFrameLength(*buffer);
+if (frameLen) {
+// We've found an MP3 frame!
+// This is the first frame (and the only one we'll bother parsing), so:
+// * Mark this stream as MP3;
+// * Store the offset at which the MP3 data started; and
+// * Start buffering the frame, as it might contain handy metadata.
+// We're now sure this is an MP3 stream.
+mIsMP3 = DEFINITELY_MP3;
+// We need to know these to convert the number of frames in the stream
+// to the length of the stream in seconds.
+mSamplesPerSecond = mMP3Parser.GetSampleRate();
+mSamplesPerFrame = mMP3Parser.GetSamplesPerFrame();
+// If the stream has a constant bitrate, we should only need the length
+// of the first frame and the length (in bytes) of the stream to
+// estimate the length (in seconds).
+mTotalFrameSize += frameLen;
+mFrameCount++;
+// If |mMP3Offset| isn't set then this is the first MP3 frame we have
+// seen in the stream, which is useful for duration estimation.
+if (mMP3Offset > -1) {
+uint16_t skip = frameLen - sizeof(MP3Frame);
+buffer += skip ? skip : 1;
+continue;
+}
+// Remember the offset of the MP3 stream.
+// We're at the last byte of an MP3Frame, so MP3 data started
+// sizeof(MP3Frame) - 1 bytes ago.
+mMP3Offset = aStreamOffset
++ (buffer - aBuffer)
+- (sizeof(MP3Frame) - 1);
+buffer++;
+// If the stream has a variable bitrate, the first frame has metadata
+// we need for duration estimation and seeking. Start buffering it so we
+// can parse it later.
+mFirstFrameEnd = mMP3Offset + frameLen;
+uint64_t currOffset = buffer - aBuffer + aStreamOffset;
+uint64_t copyLen = std::min(mFirstFrameEnd - currOffset,
+(uint64_t)(bufferEnd - buffer));
+mFirstFrame.Append((const char *)buffer, copyLen);
+buffer += copyLen;
+} else {
+// Nothing to see here. Move along.
+buffer++;
+}
+}
+*aOutBytesRead = buffer - aBuffer;
+if (mFirstFrameEnd > -1 && mFirstFrameEnd <= aStreamOffset + buffer - aBuffer) {
+// We have our whole first frame. Try to find a VBR header.
+mNumFrames = FindNumVBRFrames(mFirstFrame);
+mFirstFrameEnd = -1;
+}
+return NS_OK;
+}
+void MP3FrameParser::Parse(const char* aBuffer, uint32_t aLength, uint64_t aOffset)
+{
+MutexAutoLock mon(mLock);
+if (HasExactDuration()) {
+// We know the duration; nothing to do here.
+return;
+}
+const uint8_t* buffer = reinterpret_cast<const uint8_t*>(aBuffer);
+int32_t length = aLength;
+uint64_t offset = aOffset;
+// Got some data we have seen already. Skip forward to what we need.
+if (aOffset < mOffset) {
+buffer += mOffset - aOffset;
+length -= mOffset - aOffset;
+offset = mOffset;
+if (length <= 0) {
+return;
+}
+}
+// If there is a discontinuity in the input stream, reset the state of the
+// parsers so we don't get any partial headers.
+if (mOffset < aOffset) {
+if (!mID3Parser.IsParsed()) {
+// Only reset this if it hasn't finished yet.
+mID3Parser.Reset();
+}
+if (mFirstFrameEnd > -1) {
+NS_WARNING("Discontinuity in input while buffering first frame.");
+mFirstFrameEnd = -1;
+}
+mMP3Parser.Reset();
+}
+uint32_t bytesRead = 0;
+if (NS_FAILED(ParseBuffer(buffer,
+length,
+offset,
+&bytesRead))) {
+return;
+}
+MOZ_ASSERT(length <= (int)bytesRead, "All bytes should have been consumed");
+// Update next data offset
+mOffset = offset + bytesRead;
+// If we've parsed lots of data and we still have nothing, just give up.
+// We don't count ID3 headers towards the skipped bytes count, as MP3 files
+// can have massive ID3 sections.
+if (!mID3Parser.IsParsed() && mMP3Offset < 0 &&
+mOffset - mTotalID3Size > MAX_SKIPPED_BYTES) {
+mIsMP3 = NOT_MP3;
+}
+}
+int64_t MP3FrameParser::GetDuration()
+{
+MutexAutoLock mon(mLock);
+if (!ParsedHeaders() || !mSamplesPerSecond) {
+// Not a single frame decoded yet.
+return -1;
+}
+MOZ_ASSERT(mFrameCount > 0 && mTotalFrameSize > 0,
+"Frame parser should have seen at least one MP3 frame of positive length.");
+if (!mFrameCount || !mTotalFrameSize) {
+// This should never happen.
+return -1;
+}
+double frames;
+if (mNumFrames < 0) {
+// Estimate the number of frames in the stream based on the average frame
+// size and the length of the MP3 file.
+double frameSize = (double)mTotalFrameSize / mFrameCount;
+frames = (double)(mLength - mMP3Offset) / frameSize;
+} else {
+// We know the exact number of frames from the VBR header.
+frames = mNumFrames;
+}
+// The duration of each frame is constant over a given stream.
+double usPerFrame = USECS_PER_S * mSamplesPerFrame / mSamplesPerSecond;
+return frames * usPerFrame;
+}
+int64_t MP3FrameParser::GetMP3Offset()
+{
+MutexAutoLock mon(mLock);
+return mMP3Offset;
+}
+bool MP3FrameParser::ParsedHeaders()
+{
+// We have seen both the beginning and the end of the first MP3 frame in the
+// stream.
+return mMP3Offset > -1 && mFirstFrameEnd < 0;
+}
+bool MP3FrameParser::HasExactDuration()
+{
+return ParsedHeaders() && mNumFrames > -1;
+}
+bool MP3FrameParser::NeedsData()
+{
+// If we don't know the duration exactly then either:
+//  - we're still waiting for a VBR header; or
+//  - we look at all frames to constantly update our duration estimate.
+return IsMP3() && !HasExactDuration();
+}
+}

The Tor Browser / file comparison

comparison: content/media/MP3FrameParser.cpp

content/media/MP3FrameParser.cpp