PureBoard

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public class Mp3Tools
{
	private static final int[] bitRatesV1L1	= {0, 32, 64, 96,128,160,192,224,256,288,320,352,384,416,448};
	private static final int[] bitRatesV1L2	= {0, 32, 48, 56, 64, 80, 93,112,128,160,192,224,256,320,384};
	private static final int[] bitRatesV1L3	= {0, 32, 40, 48, 56, 64, 80, 96,112,128,160,192,224,256,320};
	
	private static final int[] bitRatesV2L1 = {0, 32, 48, 56, 64, 80, 96,112,128,114,160,176,192,224,256};
	private static final int[] bitRatesV2L2 = {0,  8, 16, 24, 32, 40, 48, 56, 64, 80, 96,112,128,114,160};
	private static final int[] bitRatesV2L3 = {0,  8, 16, 24, 32, 40, 48, 56, 64, 80, 96,112,128,114,160};
	
	private static final int[][] bitRatesV1 = {bitRatesV1L1, bitRatesV1L2, bitRatesV1L3};
	private static final int[][] bitRatesV2 = {bitRatesV2L1, bitRatesV2L2, bitRatesV2L3};
	
	private static final int[][][] bitRates = {bitRatesV1, bitRatesV2};

	// ---
	
	private static final int[] sampleRates0	= {11025, 12000,  8000};
	private static final int[] sampleRates2	= {22050, 24000, 16000};
	private static final int[] sampleRates3	= {44100, 48000, 32000};
	
	private static final int[][] sampleRates	= {sampleRates0, null, sampleRates2, sampleRates3};
	
	// ---
	
	/**
	 * Returns the length of an mp3 file in milliseconds
	 */
    public static long getMp3Length(InputStream inStream)
    throws IOException
    {
    	float length = -1;
    	
		int b = 0;
		int c = 0;
        @SuppressWarnings("unused")
		int d = 0;
		
		while(b > -1)
		{
			b = inStream.read();
			
			if (b == 0xFF)
			{
				b = inStream.read();
				
				if ((b & 0xE0) == 0xE0)
				{
					c = inStream.read();
					d = inStream.read();
					
					int mpegVersion		= (b & 0x18) >> 3;
    				int mpegLayer		= (b & 0x06) >> 1;
    				int bitrateIndex	= (c & 0xF0) >> 4;
    				int samplerateIndex	= (c & 0x0C) >> 2;
    				int padding			= (c & 0x02) >> 1;
    				
    				/*
    				if (mpegVersion == 1 || mpegLayer == 0 || bitrateIndex == 0x0F || samplerateIndex == 0x03)
    					continue;
    				*/
    				
    				int bitrate = getMp3Bitrate(mpegVersion, mpegLayer, bitrateIndex);
    				int samplerate = getMp3Samplerate(mpegVersion, samplerateIndex);
    				
    				int frameSize = 144 * (bitrate * 1000) / samplerate + padding;
    				inStream.skip(frameSize - 4);
    				
    				/*
    				System.out.println("mpegVersion     = " + mpegVersion);
    				System.out.println("mpegLayer       = " + mpegLayer);
    				System.out.println("bitrateIndex    = " + bitrateIndex + "\t -> " + bitrate);
    				System.out.println("samplerateIndex = " + samplerateIndex + "\t -> " + samplerate);
    				System.out.println("padding         = " + padding);
    				System.out.println("------------------------------------");
    				*/
    				
    				length += frameSize / (bitrate / 8);
				}
			}
		}
    	
    	return (long)length;
    }
    
    
    private static int getMp3Bitrate(int mpegVersion, int mpegLayer, int bitrateIndex)
    {
    	switch(mpegVersion)
    	{
    	case 0: mpegVersion = 1; break;
    	case 2: mpegVersion = 1; break;
    	case 3: mpegVersion = 0; break;
    	}
    	
    	mpegLayer = 3 - mpegLayer;
    	
    	return bitRates[mpegVersion][mpegLayer][bitrateIndex];
    }
    
    
    private static int getMp3Samplerate(int mpegVersion, int samplerateIndex)
    {
    	return sampleRates[mpegVersion][samplerateIndex];
    }
}