gecko-dev/content/media/MP3FrameParser.cpp

389 строки
11 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 <algorithm>
#include "nsMemory.h"
#include "MP3FrameParser.h"
#include "VideoUtils.h"
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];
}
/** 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;
}
/** 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 = 200 * 1024;
// 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"),
mTotalFrameSize(0),
mNumFrames(0),
mOffset(0),
mLength(aLength),
mMP3Offset(-1),
mSampleRate(0),
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;
// Yes, this is an MP3!
mIsMP3 = DEFINITELY_MP3;
mID3Parser.Reset();
}
}
}
while (buffer < bufferEnd) {
uint16_t frameLen = mMP3Parser.ParseFrameLength(*buffer);
if (frameLen) {
if (mMP3Offset < 0) {
// Found our first frame: mark this stream as MP3 and let the decoder
// know where in the stream the MP3 data starts.
mIsMP3 = DEFINITELY_MP3;
// We're at the last byte of an MP3Frame, so MP3 data started
// sizeof - 1 bytes ago.
mMP3Offset = aStreamOffset
+ (buffer - aBuffer)
- (sizeof(MP3Frame) - 1);
}
mSampleRate = mMP3Parser.GetSampleRate();
mTotalFrameSize += frameLen;
mNumFrames++;
buffer += frameLen - sizeof(MP3Frame);
} else {
buffer++;
}
}
*aOutBytesRead = buffer - aBuffer;
return NS_OK;
}
void MP3FrameParser::Parse(const char* aBuffer, uint32_t aLength, int64_t aOffset)
{
MutexAutoLock mon(mLock);
const uint8_t* buffer = reinterpret_cast<const uint8_t*>(aBuffer);
int32_t length = aLength;
int64_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();
}
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.
if (!mID3Parser.IsParsed() && !mNumFrames && mOffset > MAX_SKIPPED_BYTES) {
mIsMP3 = NOT_MP3;
}
}
int64_t MP3FrameParser::GetDuration()
{
MutexAutoLock mon(mLock);
if (!mNumFrames || !mSampleRate) {
return -1; // Not a single frame decoded yet
}
// Estimate the total number of frames in the file from the average frame
// size we've seen so far, and the length of the file.
double avgFrameSize = (double)mTotalFrameSize / mNumFrames;
// Need to cut out the header here. Ignore everything up to the first MP3
// frames.
double estimatedFrames = (double)(mLength - mMP3Offset) / avgFrameSize;
// The duration of each frame is constant over a given stream.
double usPerFrame = USECS_PER_S * SAMPLES_PER_FRAME / mSampleRate;
return estimatedFrames * usPerFrame;
}
int64_t MP3FrameParser::GetMP3Offset()
{
MutexAutoLock mon(mLock);
return mMP3Offset;
}
}