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116 lines
4.0 KiB
C++
116 lines
4.0 KiB
C++
/* -*- Mode: C++; tab-width: 2; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
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/* vim:set ts=2 sw=2 sts=2 et cindent: */
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/* This Source Code Form is subject to the terms of the Mozilla Public
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* License, v. 2.0. If a copy of the MPL was not distributed with this
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* file, You can obtain one at http://mozilla.org/MPL/2.0/. */
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#include <stdint.h>
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#include "mozilla/Mutex.h"
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namespace mozilla {
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// A description of the MP3 format and its extensions is available at
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//
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// http://www.codeproject.com/Articles/8295/MPEG-Audio-Frame-Header
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//
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// The data in MP3 streams is split into small frames, with each frame
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// containing a fixed number of samples. The duration of a frame depends
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// on the frame's bit rate and sample rate. Both values can vary among
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// frames, so it is necessary to examine each individual frame of an MP3
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// stream to calculate the stream's overall duration.
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//
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// The MP3 frame parser extracts information from an MP3 data stream. It
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// accepts a range of frames of an MP3 stream as input, and parses all
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// frames for their duration. Callers can query the stream's overall
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// duration from the parser.
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//
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// Call the methods NotifyDataArrived or Parse to add new data. If you added
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// information for a certain stream position, you cannot go back to previous
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// positions. The parser will simply ignore the input. If you skip stream
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// positions, the duration of the related MP3 frames will be estimated from
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// the stream's average.
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//
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// The method GetDuration returns calculated duration of the stream, including
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// estimates for skipped ranges.
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//
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// All public methods are thread-safe.
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class MP3FrameParser
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{
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public:
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MP3FrameParser(int64_t aLength=-1);
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bool IsMP3() {
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MutexAutoLock mon(mLock);
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return mIsMP3 != NOT_MP3;
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}
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void Parse(const char* aBuffer, uint32_t aLength, int64_t aStreamOffset);
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// Returns the duration, in microseconds. If the entire stream has not
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// been parsed yet, this is an estimate based on the bitrate of the
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// frames parsed so far.
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int64_t GetDuration();
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// Returns the offset of the first MP3 frame in the stream, or -1 of
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// no MP3 frame has been detected yet.
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int64_t GetMP3Offset();
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private:
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// Parses aBuffer, starting at offset 0. Returns the number of bytes
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// parsed, relative to the start of the buffer. Note this may be
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// greater than aLength if the headers in the buffer indicate that
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// the frame or ID3 tag extends outside of aBuffer. Returns failure
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// if too many non-MP3 bytes are parsed.
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nsresult ParseBuffer(const uint8_t* aBuffer,
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uint32_t aLength,
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int64_t aStreamOffset,
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uint32_t* aOutBytesRead);
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// mBuffer must be at least 19 bytes long, in case the last byte in the
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// buffer is the first byte in a 10 byte long ID3 tag header.
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uint8_t mBuffer[32];
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uint32_t mBufferLength;
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// A low-contention lock for protecting the parser results
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Mutex mLock;
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// All fields below are protected by mLock
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uint64_t mDurationUs;
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uint64_t mBitRateSum;
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uint64_t mTotalFrameSize;
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uint64_t mNumFrames;
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// Offset of the last data parsed. This is the end offset of the last data
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// block parsed, so it's the start offset we expect to get on the next
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// call to Parse().
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int64_t mOffset;
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// Total length of the stream in bytes.
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int64_t mLength;
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// Offset of first MP3 frame in the bitstream. Has value -1 until the
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// first MP3 frame is found.
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int64_t mMP3Offset;
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// Count of bytes that have been parsed but skipped over because we couldn't
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// find a sync pattern or an ID3 header. If this gets too high, we assume
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// the stream either isn't MP3, or is corrupt.
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uint32_t mSkippedBytes;
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// Number of audio samples per second. Fixed through the whole file.
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uint16_t mSampleRate;
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enum eIsMP3 {
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MAYBE_MP3, // We're giving the stream the benefit of the doubt...
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DEFINITELY_MP3, // We've hit at least one ID3 tag or MP3 frame.
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NOT_MP3 // Not found any evidence of the stream being MP3.
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};
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eIsMP3 mIsMP3;
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};
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}
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