RTP payload type 8 G711 AlAW RTP

Question

Hi everybody,
I look for a decoder to decode ALAW_RTP. For my project I have to save RTP stream (a-law and not mu-law) to a wave file.
I found this in the forum : http://forum.java.sun.com/thread.jspa?forumID=28&threadID=505153
But they don't put a solution for this problem.
Is anybody solve this problem?
How can i create the DePackatazer for ALAW_RTP?
Please help!
Gassman

Answer 1

I find the solution :
It's a mixe between the link upside, com.ibm.media.codec.alaw.JavaDecoder, com.ibm.media.codec.ulaw.JavaDecoder and http://java.sun.com/products/java-media/jmf/2.1.1/solutions/PcmDepacketizer.java
class AlawRtpDecoder.java
import javax.media.Buffer;
import javax.media.Control;
import javax.media.Format;
import javax.media.format.AudioFormat;
import com.sun.media.controls.SilenceSuppressionAdapter;
* Mu-Law to PCM java decoder
* @Author Shay Ben-David [email protected]
public class AlawRtpDecoder extends com.ibm.media.codec.audio.AudioCodec {
     // Variables
     static private final byte[] lutTableL = new byte[256];
     static private final byte[] lutTableH = new byte[256];
     static String PLUGIN_NAME = "ALAW_RTP DePacketizer";
     static String CUSTOM_PCM = "alaw/rtp";
     static int DEFAULT_RATE = 8000;
     static int DEFAULT_SIZE = 16;
     static int DEFAULT_CHNLS = 1;
     // Methods
     public AlawRtpDecoder() {
          supportedInputFormats = new AudioFormat[] { new AudioFormat(CUSTOM_PCM) };
          // We have to assume some defaults for the output
          // format. Otherwise, the data flow graph cannot
          // be initialized.
          supportedOutputFormats = new AudioFormat[] { new AudioFormat(
                    AudioFormat.LINEAR, DEFAULT_RATE, DEFAULT_SIZE, DEFAULT_CHNLS) };
     protected Format[] getMatchingOutputFormats(Format in) {
          AudioFormat af = (AudioFormat) in;
          supportedOutputFormats = new AudioFormat[] { new AudioFormat(
                    AudioFormat.LINEAR, af.getSampleRate(), 16, af.getChannels(),
                    AudioFormat.LITTLE_ENDIAN, // isBigEndian(),
                    AudioFormat.SIGNED // isSigned());
          return supportedOutputFormats;
     /** Initializes the codec. * */
     public void open() {
          initTables();
     public String getName() {
          return PLUGIN_NAME;
     static public boolean matche(Format input, Format supported[]) {
          for (int i = 0; i < supported.length; i++) {
               if (input.matches(supported))
                    return true;
          return false;
     public Format[] getSupportedOutputFormats(Format input) {
          if (input == null || matche(input, supportedInputFormats)) {
               return supportedOutputFormats;
          return new Format[0];
     public Format setInputFormat(Format format) {
          if (!matche(format, supportedInputFormats))
               return null;
          inputFormat = (AudioFormat) format;
          return format;
     public Format setOutputFormat(Format format) {
          if (!matche(format, supportedOutputFormats))
               return null;
          outputFormat = (AudioFormat) format;
          return format;
     public Format[] getSupportedInputFormats() {
          return supportedInputFormats;
     protected Format getInputFormat() {
          return inputFormat;
     protected Format getOutputFormat() {
          return outputFormat;
     public void close() {
     /** decode the buffer * */
     public int process(Buffer inputBuffer, Buffer outputBuffer) {
          if (!checkInputBuffer(inputBuffer)) {
               return BUFFER_PROCESSED_FAILED;
          if (isEOM(inputBuffer)) {
               propagateEOM(outputBuffer);
               return BUFFER_PROCESSED_OK;
          byte[] inData = (byte[]) inputBuffer.getData();
          byte[] outData = validateByteArraySize(outputBuffer, inData.length * 2);
          int inpLength = inputBuffer.getLength();
          int outLength = 2 * inpLength;
          int inOffset = inputBuffer.getOffset();
          int outOffset = outputBuffer.getOffset();
          for (int i = 0; i < inpLength; i++) {
               int temp = inData[inOffset++] & 0xff;
               outData[outOffset++] = lutTableL[temp];
               outData[outOffset++] = lutTableH[temp];
          updateOutput(outputBuffer, outputFormat, outLength, outputBuffer.getOffset());
          return BUFFER_PROCESSED_OK;
     private void initTables (){
     for (int i=0;i<256;i++) {
     int input = i ^ 0x55;
     int mantissa = (input & 0xf ) << 4;
     int segment = (input & 0x70) >> 4;
     int value = mantissa+8;
     if (segment>=1)
     value+=0x100;
     if (segment>1)
     value <<= (segment - 1);
     if ( (input & 0x80)==0 )
     value = -value;
     lutTableL[i]=(byte)value;
     lutTableH[i]=(byte)(value>>8);
     public java.lang.Object[] getControls() {
          if (controls == null) {
               controls = new Control[1];
               controls[0] = new SilenceSuppressionAdapter(this, false, false);
          return (Object[]) controls;
for use this juste add the following codec in your main program
RTPManager manager = RTPManager.newInstance();
AlawRtpDecoder alawRtpDepktizer = null;
          try
alawRtpDepktizer = new AlawRtpDecoder();
               PlugInManager.addPlugIn(alawRtpDepktizer.getClass().getName(),
                         alawRtpDepktizer.getSupportedInputFormats(),
                         alawRtpDepktizer.getSupportedOutputFormats(null),
                         PlugInManager.CODEC);
               Format AlawRtpFormat =(alawRtpDepktizer.getSupportedInputFormats())[0];
               manager.addFormat(AlawRtpFormat, 8);
}null