g711u.java

package javaforce.voip;

/*
 struct rtp_header {
 byte version;  //usually 0x80
 byte type;  //0x00
 short seqnum;
 int timestamp;
 int syncsrcid;
 };
 */

import javaforce.*;

/**
 * Encodes/decodes g711 packets (U-Law). (North America format)
 */

public class g711u implements Coder {

  private RTP rtp;

  public g711u(RTP rtp) {
    this.rtp = rtp;
  }
  private static short ulaw_lut[];  //signed
  private static short etab[] = {0, 132, 396, 924, 1980, 4092, 8316, 16764};
  private static int exp_lut[] = {
    0, 0, 1, 1, 2, 2, 2, 2, 3, 3, 3, 3, 3, 3, 3, 3,
    4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4,
    5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5,
    5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5,
    6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6,
    6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6,
    6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6,
    6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6,
    7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7,
    7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7,
    7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7,
    7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7,
    7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7,
    7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7,
    7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7,
    7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7
  };

  static {
    g711u.init();
  }

  /** init the decode lookup table (256 entries) */
  private static void init() {
    short mu, e, f, y;
    ulaw_lut = new short[256];
    for (short i = 0; i < 256; i++) {
      mu = (short) (255 - i);
      e = (short) ((mu & 0x70) / 16);
      f = (short) (mu & 0x0f);
      y = (short) (f * (1 << (e + 3)));
      y += etab[e];
      if ((mu & 0x80) == 0x80) {
        y = (short) -y;
      }
      ulaw_lut[i] = y;
    }
  }
  private static final short BIAS = 0x84;
  private static final short CLIP = 32635;  //not MAX short

  private byte encoded[] = new byte[160 + 12];

  //samples must be 160 samples
  public byte[] encode(short samples[]) {
    int sign, exponent, mantissa;
    byte ulawbyte;
    short sample;
    RTPChannel rtpChannel = rtp.getDefaultChannel();

    rtpChannel.buildHeader(encoded, 0, rtpChannel.getseqnum(), rtpChannel.gettimestamp(160), rtpChannel.getssrc(), false);

    for (int i = 0; i < 160; i++) {
      /* Get the sample into sign-magnitude. */
      sample = samples[i];
      sign = (sample >> 8) & 0x80;          /* set aside the sign */
      if (sign != 0) {
        sample = (short) -sample;      /* get magnitude */
      }
      if (sample > CLIP) {
        sample = CLIP;     /* clip the magnitude */
      }
      /* Convert from 16 bit linear to ulaw. */
      sample += BIAS;
      exponent = exp_lut[(sample >> 7) & 0xff];
      mantissa = ((sample >> (exponent + 3)) & 0x0f);
      ulawbyte = (byte) (~(sign | (exponent << 4) | mantissa));
      if (ulawbyte == 0) {
        ulawbyte = 0x02;   /* optional CCITT trap */
      }
      encoded[12 + i] = ulawbyte;
    }
    return encoded;
  }

  private int decode_timestamp;

  private short decoded[] = new short[160];

  //encoded must be 160+12 bytes at least
  public short[] decode(byte encoded[], int off) {
    int decode_timestamp = BE.getuint32(encoded, off + 4);
    if (this.decode_timestamp == 0) {
      this.decode_timestamp = decode_timestamp;
    } else {
      if (RTP.debug) {
        JFLog.log("G711u:timestamp = " + decode_timestamp + ":" + ((this.decode_timestamp + 160 == decode_timestamp) ? "ok" : "lost packet"));
      }
      this.decode_timestamp = decode_timestamp;
    }
    //skip first 12 bytes (RTP header)
    for (int i = 0; i < 160; i++) {
      decoded[i] = ulaw_lut[encoded[off + i + 12] & 0xff];
    }
    return decoded;
  }

  public int getSampleRate() {return 8000;}
}