ogginforeader.java

YOYOPlayer MP3播放器 java+JMF实现

/*
 * Entagged Audio Tag library
 * Copyright (c) 2003-2005 Rapha�l Slinckx <[e-mail]>
 * Copyright (c) 2004-2005 Christian Laireiter <[e-mail]>
 * 
 * This library is free software; you can redistribute it and/or
 * modify it under the terms of the GNU Lesser General Public
 * License as published by the Free Software Foundation; either
 * version 2.1 of the License, or (at your option) any later version.
 *  
 * This library is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
 * Lesser General Public License for more details.
 * 
 * You should have received a copy of the GNU Lesser General Public
 * License along with this library; if not, write to the Free Software
 * Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA  02110-1301  USA
 */
package com.hadeslee.audiotag.audio.ogg.util;

import com.hadeslee.audiotag.audio.exceptions.CannotReadException;
import com.hadeslee.audiotag.audio.generic.GenericAudioHeader;

import java.io.*;
import java.util.logging.Logger;

/**
 * Read encoding info, only implemented for vorbis streams
 */
public class OggInfoReader
{
    // Logger Object
    public static Logger logger = Logger.getLogger("com.hadeslee.jaudiotagger.audio.ogg.atom");

    public GenericAudioHeader read(RandomAccessFile raf) throws CannotReadException, IOException
    {
        GenericAudioHeader info = new GenericAudioHeader();
        logger.fine("Started");
        long oldPos = 0;

        //TODO this code appears to work backwards from file looking for the last ogg page, it reads
        //the granule position for this last page which must be set. I dont really understand
        //why it does this check. But I think it is an arbitary check to make sure weve read the file correctly
        raf.seek(0);
        double pcmSamplesNumber = -1;
        raf.seek(raf.length() - 2);
        while (raf.getFilePointer() >= 4)
        {
            if (raf.read() == OggPageHeader.CAPTURE_PATTERN[3])
            {
                raf.seek(raf.getFilePointer() - OggPageHeader.FIELD_CAPTURE_PATTERN_LENGTH );
                byte[] ogg = new byte[3];
                raf.readFully(ogg);
                if (ogg[0] == OggPageHeader.CAPTURE_PATTERN[0]
                    && ogg[1] == OggPageHeader.CAPTURE_PATTERN[1]
                    && ogg[2] == OggPageHeader.CAPTURE_PATTERN[2])
                {
                    raf.seek(raf.getFilePointer() - 3);

                    oldPos = raf.getFilePointer();
                    raf.seek(raf.getFilePointer() + OggPageHeader.FIELD_PAGE_SEGMENTS_POS);
                    int pageSegments = raf.readByte() & 0xFF; //Unsigned
                    raf.seek(oldPos);

                    byte[] b = new byte[OggPageHeader.OGG_PAGE_HEADER_FIXED_LENGTH + pageSegments];
                    raf.readFully(b);

                    OggPageHeader pageHeader = new OggPageHeader(b);
                    raf.seek(0);
                    pcmSamplesNumber = pageHeader.getAbsoluteGranulePosition();
                    break;
                }
            }
            raf.seek(raf.getFilePointer() - 2);
        }

        if (pcmSamplesNumber == -1)
        {
            //According to spec a value of -1 indicates no packet finished on this page, this should not occurt
            throw new CannotReadException("Error: Could not find the Ogg Setup block");
        }

        //1st page = Identifaction Header
        OggPageHeader pageHeader = OggPageHeader.read (raf);
        byte[] vorbisData = new byte[pageHeader.getPageLength()];
        raf.read(vorbisData);
        VorbisIdentificationHeader vorbisIdentificationHeader = new VorbisIdentificationHeader(vorbisData);

        //Map to generic encodingInfo
        info.setPreciseLength((float) (pcmSamplesNumber / vorbisIdentificationHeader.getSamplingRate()));
        info.setChannelNumber(vorbisIdentificationHeader.getChannelNumber());
        info.setSamplingRate(vorbisIdentificationHeader.getSamplingRate());
        info.setEncodingType(vorbisIdentificationHeader.getEncodingType());
        info.setExtraEncodingInfos("");

        //TODO this calculation should be done within identification header
        if (vorbisIdentificationHeader.getNominalBitrate() != 0
            && vorbisIdentificationHeader.getMaxBitrate() == vorbisIdentificationHeader.getNominalBitrate()
            && vorbisIdentificationHeader.getMinBitrate() == vorbisIdentificationHeader.getNominalBitrate())
        {
            //CBR (in kbps)
            info.setBitrate(vorbisIdentificationHeader.getNominalBitrate() / 1000);
            info.setVariableBitRate(false);
        }
        else if (vorbisIdentificationHeader.getNominalBitrate() != 0 && vorbisIdentificationHeader.getMaxBitrate() == 0
            && vorbisIdentificationHeader.getMinBitrate() == 0)
        {
            //Average vbr (in kpbs)
            info.setBitrate(vorbisIdentificationHeader.getNominalBitrate() / 1000);
            info.setVariableBitRate(true);
        }
        else
        {
            //TODO need to remove comment from raf.getLength()
            info.setBitrate(computeBitrate(info.getTrackLength(), raf.length()));
            info.setVariableBitRate(true);
        }
        logger.fine("Finished");
        return info;
    }

    private int computeBitrate(int length, long size)
    {
        return (int) ((size / 1000) * 8 / length);
    }
}