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

--1:000000000000
+:b437b6198495
+/* -*- 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/. */
+#ifndef MP3FrameParser_h
+#define MP3FrameParser_h
+#include <stdint.h>
+#include "mozilla/Mutex.h"
+#include "nsString.h"
+namespace mozilla {
+// Simple parser to tell whether we've found an ID3 header and how long it is,
+// so that we can skip it.
+// XXX maybe actually parse this stuff?
+class ID3Parser
+{
+public:
+ID3Parser();
+void Reset();
+bool ParseChar(char ch);
+bool IsParsed() const;
+uint32_t GetHeaderLength() const;
+private:
+uint32_t mCurrentChar;
+uint32_t mHeaderLength;
+};
+struct MP3Frame {
+uint16_t mSync1 : 8;      // Always all set
+uint16_t mProtected : 1;  // Ignored
+uint16_t mLayer : 2;
+uint16_t mVersion : 2;
+uint16_t mSync2 : 3;      // Always all set
+uint16_t mPrivate : 1;    // Ignored
+uint16_t mPad : 1;
+uint16_t mSampleRate : 2; // Index into mpeg_srates above
+uint16_t mBitrate : 4;    // Index into mpeg_bitrates above
+uint16_t CalculateLength();
+};
+// Buffering parser for MP3 frames.
+class MP3Parser
+{
+public:
+MP3Parser();
+// Forget all data the parser has seen so far.
+void Reset();
+// Parse the given byte. If we have found a frame header, return the length of
+// the frame.
+uint16_t ParseFrameLength(uint8_t ch);
+// Get the sample rate from the current header.
+uint32_t GetSampleRate();
+// Get the number of samples per frame.
+uint32_t GetSamplesPerFrame();
+private:
+uint32_t mCurrentChar;
+union {
+uint8_t mRaw[3];
+MP3Frame mFrame;
+} mData;
+};
+// A description of the MP3 format and its extensions is available at
+//
+//  http://www.codeproject.com/Articles/8295/MPEG-Audio-Frame-Header
+//
+// The data in MP3 streams is split into small frames, with each frame
+// containing a fixed number of samples. The duration of a frame depends
+// on the frame's bit rate and sample rate. Both values can vary among
+// frames, so it is necessary to examine each individual frame of an MP3
+// stream to calculate the stream's overall duration.
+//
+// The MP3 frame parser extracts information from an MP3 data stream. It
+// accepts a range of frames of an MP3 stream as input, and parses all
+// frames for their duration. Callers can query the stream's overall
+// duration from the parser.
+//
+// Call the methods NotifyDataArrived or Parse to add new data. If you added
+// information for a certain stream position, you cannot go back to previous
+// positions. The parser will simply ignore the input. If you skip stream
+// positions, the duration of the related MP3 frames will be estimated from
+// the stream's average.
+//
+// The method GetDuration returns calculated duration of the stream, including
+// estimates for skipped ranges.
+//
+// All public methods are thread-safe.
+class MP3FrameParser
+{
+public:
+MP3FrameParser(int64_t aLength=-1);
+bool IsMP3() {
+MutexAutoLock mon(mLock);
+return mIsMP3 != NOT_MP3;
+}
+void Parse(const char* aBuffer, uint32_t aLength, uint64_t aStreamOffset);
+// Returns the duration, in microseconds. If the entire stream has not
+// been parsed yet, this is an estimate based on the bitrate of the
+// frames parsed so far.
+int64_t GetDuration();
+// Returns the offset of the first MP3 frame in the stream, or -1 of
+// no MP3 frame has been detected yet.
+int64_t GetMP3Offset();
+// Returns true if we've seen the whole first frame of the MP3 stream, and
+// therefore can make an estimate on the stream duration.
+// Otherwise, returns false.
+bool ParsedHeaders();
+// Returns true if we know the exact duration of the MP3 stream;
+// false otherwise.
+bool HasExactDuration();
+// Returns true if the parser needs more data for duration estimation.
+bool NeedsData();
+private:
+// Parses aBuffer, starting at offset 0. Returns the number of bytes
+// parsed, relative to the start of the buffer. Note this may be
+// greater than aLength if the headers in the buffer indicate that
+// the frame or ID3 tag extends outside of aBuffer. Returns failure
+// if too many non-MP3 bytes are parsed.
+nsresult ParseBuffer(const uint8_t* aBuffer,
+uint32_t aLength,
+int64_t aStreamOffset,
+uint32_t* aOutBytesRead);
+// A low-contention lock for protecting the parser results
+Mutex mLock;
+// ID3 header parser. Keeps state between reads in case the header falls
+// in between.
+ID3Parser mID3Parser;
+// MP3 frame header parser.
+MP3Parser mMP3Parser;
+// If we read |MAX_SKIPPED_BYTES| from the stream without finding any MP3
+// frames, we give up and report |NOT_MP3|. Here we track the cumulative size
+// of any ID3 headers we've seen so big ID3 sections aren't counted towards
+// skipped bytes.
+uint32_t mTotalID3Size;
+// All fields below are protected by mLock
+// We keep stats on the size of all the frames we've seen, as well as how many
+// so that we can estimate the duration of the rest of the stream.
+uint64_t mTotalFrameSize;
+uint64_t mFrameCount;
+// Offset of the last data parsed. This is the end offset of the last data
+// block parsed, so it's the start offset we expect to get on the next
+// call to Parse().
+uint64_t mOffset;
+// Total length of the stream in bytes.
+int64_t mLength;
+// Offset of first MP3 frame in the bitstream. Has value -1 until the
+// first MP3 frame is found.
+int64_t mMP3Offset;
+// The exact number of frames in this stream, if we know it. -1 otherwise.
+int64_t mNumFrames;
+// Number of audio samples per second and per frame. Fixed through the whole
+// file. If we know these variables as well as the number of frames in the
+// file, we can get an exact duration for the stream.
+uint16_t mSamplesPerSecond;
+uint16_t mSamplesPerFrame;
+// If the MP3 has a variable bitrate, then there *should* be metadata about
+// the encoding in the first frame. We buffer the first frame here.
+nsAutoCString mFirstFrame;
+// While we are reading the first frame, this is the stream offset of the
+// last byte of that frame. -1 at all other times.
+int64_t mFirstFrameEnd;
+enum eIsMP3 {
+MAYBE_MP3, // We're giving the stream the benefit of the doubt...
+DEFINITELY_MP3, // We've hit at least one ID3 tag or MP3 frame.
+NOT_MP3 // Not found any evidence of the stream being MP3.
+};
+eIsMP3 mIsMP3;
+};
+}
+#endif

The Tor Browser / file comparison

comparison: content/media/MP3FrameParser.h

content/media/MP3FrameParser.h