The Tor Browser: content/media/MP3FrameParser.cpp@6474c204b198 (annotated)

content/media/MP3FrameParser.cpp@6474c204b198 (annotated)

content/media/MP3FrameParser.cpp

Wed, 31 Dec 2014 06:09:35 +0100

author: Michael Schloh von Bennewitz <michael@schloh.com>
date: Wed, 31 Dec 2014 06:09:35 +0100
changeset 0: 6474c204b198
permissions: -rw-r--r--

Cloned upstream origin tor-browser at tor-browser-31.3.0esr-4.5-1-build1
revision ID fc1c9ff7c1b2defdbc039f12214767608f46423f for hacking purpose.

 /* -*- 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();
 }
 }

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content/media/MP3FrameParser.cpp@6474c204b198 (annotated)

content/media/MP3FrameParser.cpp