mulawdecoderutil.java

FMJ（freedom media for java)是java视频开发的新选择

package net.sf.fmj.media.codec.audio.ulaw;



/**
 *  Turns 8-bit mu-law bytes back into 16-bit PCM values.
 * Adapted from code by Marc Sweetgall at http://www.codeproject.com/csharp/g711audio.asp
 * Note: in .Net, a byte is unsigned, hence the need to always do byte & 0xff - this converts an unsigned byte to the corresponding (nonnegative) int value.
 */
public class MuLawDecoderUtil
{
    /**
     *  An array where the index is the mu-law input, and the value is
     *  the 16-bit PCM result.
     *  
     */
    private static short[] muLawToPcmMap;

    static
    {
        muLawToPcmMap = new short[256];
        for (short i = 0; i < muLawToPcmMap.length; i++)
            muLawToPcmMap[i] = decode((byte) i);
    }

    /**
     *  Decode one mu-law byte. For internal use only.
     *  
     *  @param mulaw The encoded mu-law byte
     *  @return A short containing the 16-bit result
     */
    private static short decode(byte mulaw)
    {
        //Flip all the bits
        mulaw = (byte)~mulaw;

        //Pull out the value of the sign bit
        int sign = mulaw & 0x80;
        //Pull out and shift over the value of the exponent
        int exponent = (mulaw & 0x70) >> 4;
        //Pull out the four bits of data
        int data = mulaw & 0x0f;

        //Add on the implicit fifth bit (we know the four data bits followed a one bit)
        data |= 0x10;
        /* Add a 1 to the end of the data by shifting over and adding one.  Why?
         * Mu-law is not a one-to-one function.  There is a range of values that all
         * map to the same mu-law byte.  Adding a one to the end essentially adds a
         * "half byte", which means that the decoding will return the value in the
         * middle of that range.  Otherwise, the mu-law decoding would always be
         * less than the original data. */
        data <<= 1;
        data += 1;
        /* Shift the five bits to where they need to be: left (exponent + 2) places
         * Why (exponent + 2) ?
         * 1 2 3 4 5 6 7 8 9 A B C D E F G
         * . 7 6 5 4 3 2 1 0 . . . . . . . <-- starting bit (based on exponent)
         * . . . . . . . . . . 1 x x x x 1 <-- our data
         * We need to move the one under the value of the exponent,
         * which means it must move (exponent + 2) times
         */
        data <<= exponent + 2;
        //Remember, we added to the original, so we need to subtract from the final
        data -= MuLawEncoderUtil.BIAS;
        //If the sign bit is 0, the number is positive. Otherwise, negative.
        return (short)(sign == 0 ? data : -data);
    }

    /**
     *  Decode one mu-law byte
     *  
     *  @param mulaw The encoded mu-law byte
     *  @return A short containing the 16-bit result
     */
    public static short muLawDecode(byte mulaw)
    {
        return muLawToPcmMap[mulaw & 0xff];
    }

//    /**
//     *  Decode an array of mu-law encoded bytes
//     *  
//     *  @param data An array of mu-law encoded bytes
//     *  @return An array of shorts containing the results
//     */
//    public static void muLawDecode(byte[] data, short[] decoded)
//    {
//        int size = data.length;
//        //short[] decoded = new short[size];
//        for (int i = 0; i < size; i++)
//            decoded[i] = muLawToPcmMap[data[i]];
//        //return decoded;
//    }



    /**
     *  Decode an array of mu-law encoded bytes
     *  
     *  @param data An array of mu-law encoded bytes
     *  @param decoded An array of bytes in Little-Endian format containing the results, must be twice as big as data.
     */
    public static void muLawDecodeLittleEndian(byte[] data, int offset, int len, byte[] decoded)
    {
        int size = len;
        //byte[] decoded = new byte[size * 2];
        for (int i = 0; i < size; i++)
        {
            //First byte is the less significant byte
            decoded[2 * i] = (byte)(muLawToPcmMap[data[offset + i] & 0xff] & 0xff);
            //Second byte is the more significant byte
            decoded[2 * i + 1] = (byte)(muLawToPcmMap[data[offset + i] & 0xff] >> 8);
        }
		//return decoded;
    }
    
    public static void muLawDecodeBigEndian(byte[] data, int offset, int len, byte[] decoded)
    {
        int size = len;
        //byte[] decoded = new byte[size * 2];
        for (int i = 0; i < size; i++)
        {
            //First byte is the more significant byte
            decoded[2 * i + 1] = (byte)(muLawToPcmMap[data[offset + i] & 0xff] & 0xff);
            //Second byte is the less significant byte
            decoded[2 * i] = (byte)(muLawToPcmMap[data[offset + i] & 0xff] >> 8);
        }
		//return decoded;
    }
    
    public static void muLawDecode(boolean bigEndian, byte[] data, int offset, int len, byte[] decoded)
    {
    	if (bigEndian)
    		muLawDecodeBigEndian(data, offset, len, decoded);
    	else
    		muLawDecodeLittleEndian(data, offset, len, decoded);
    }
}