RTPpacket.java

  1. //class RTPpacket
  2.  
  3. public class RTPpacket{
  4.  
  5.   //size of the RTP header:
  6.   static int HEADER_SIZE = 12;
  7.  
  8.   //Fields that compose the RTP header
  9.   public int Version;
  10.   public int Padding;
  11.   public int Extension;
  12.   public int CC;
  13.   public int Marker;
  14.   public int PayloadType;
  15.   public int SequenceNumber;
  16.   public int TimeStamp;
  17.   public int Ssrc;
  18.  
  19.   //Bitstream of the RTP header
  20.   public byte[] header;
  21.  
  22.   //size of the RTP payload
  23.   public int payload_size;
  24.   //Bitstream of the RTP payload
  25.   public byte[] payload;
  26.  
  27.  
  28.  
  29.   //--------------------------
  30.   //Constructor of an RTPpacket object from header fields and payload bitstream
  31.   //--------------------------
  32.   public RTPpacket(int PType, int Framenb, int Time, byte[] data, int data_length){
  33.     //fill by default header fields:
  34.     Version = 2;
  35.     Padding = 0;
  36.     Extension = 0;
  37.     CC = 0;
  38.     Marker = 0;
  39.     Ssrc = 0;
  40.  
  41.     //fill changing header fields:
  42.     SequenceNumber = Framenb;
  43.     TimeStamp = Time;
  44.     PayloadType = PType;
  45.  
  46.     //build the header bistream:
  47.     //--------------------------
  48.     header = new byte[HEADER_SIZE];
  49.  
  50.     //.............
  51.     //TO COMPLETE
  52.     //.............
  53.     //fill the header array of byte with RTP header fields
  54.  
  55.     //header[0] = ...
  56.     // .....
  57.  
  58.  
  59.     //fill the payload bitstream:
  60.     //--------------------------
  61.     payload_size = data_length;
  62.     payload = new byte[data_length];
  63.  
  64.     //fill payload array of byte from data (given in parameter of the constructor)
  65.     //......
  66.  
  67.     // ! Do not forget to uncomment method printheader() below !
  68.  
  69.   }
  70.  
  71.   //--------------------------
  72.   //Constructor of an RTPpacket object from the packet bistream 
  73.   //--------------------------
  74.   public RTPpacket(byte[] packet, int packet_size)
  75.   {
  76.     //fill default fields:
  77.     Version = 2;
  78.     Padding = 0;
  79.     Extension = 0;
  80.     CC = 0;
  81.     Marker = 0;
  82.     Ssrc = 0;
  83.  
  84.     //check if total packet size is lower than the header size
  85.     if (packet_size >= HEADER_SIZE) 
  86.       {
  87.     //get the header bitsream:
  88.     header = new byte[HEADER_SIZE];
  89.     for (int i=0; i < HEADER_SIZE; i++)
  90.       header[i] = packet[i];
  91.  
  92.     //get the payload bitstream:
  93.     payload_size = packet_size - HEADER_SIZE;
  94.     payload = new byte[payload_size];
  95.     for (int i=HEADER_SIZE; i < packet_size; i++)
  96.       payload[i-HEADER_SIZE] = packet[i];
  97.  
  98.     //interpret the changing fields of the header:
  99.     PayloadType = header[1] & 127;
  100.     SequenceNumber = unsigned_int(header[3]) + 256*unsigned_int(header[2]);
  101.     TimeStamp = unsigned_int(header[7]) + 256*unsigned_int(header[6]) + 65536*unsigned_int(header[5]) + 16777216*unsigned_int(header[4]);
  102.       }
  103.  }
  104.  
  105.   //--------------------------
  106.   //getpayload: return the payload bistream of the RTPpacket and its size
  107.   //--------------------------
  108.   public int getpayload(byte[] data) {
  109.  
  110.     for (int i=0; i < payload_size; i++)
  111.       data[i] = payload[i];
  112.  
  113.     return(payload_size);
  114.   }
  115.  
  116.   //--------------------------
  117.   //getpayload_length: return the length of the payload
  118.   //--------------------------
  119.   public int getpayload_length() {
  120.     return(payload_size);
  121.   }
  122.  
  123.   //--------------------------
  124.   //getlength: return the total length of the RTP packet
  125.   //--------------------------
  126.   public int getlength() {
  127.     return(payload_size + HEADER_SIZE);
  128.   }
  129.  
  130.   //--------------------------
  131.   //getpacket: returns the packet bitstream and its length
  132.   //--------------------------
  133.   public int getpacket(byte[] packet)
  134.   {
  135.     //construct the packet = header + payload
  136.     for (int i=0; i < HEADER_SIZE; i++)
  137.     packet[i] = header[i];
  138.     for (int i=0; i < payload_size; i++)
  139.     packet[i+HEADER_SIZE] = payload[i];
  140.  
  141.     //return total size of the packet
  142.     return(payload_size + HEADER_SIZE);
  143.   }
  144.  
  145.   //--------------------------
  146.   //gettimestamp
  147.   //--------------------------
  148.  
  149.   public int gettimestamp() {
  150.     return(TimeStamp);
  151.   }
  152.  
  153.   //--------------------------
  154.   //getsequencenumber
  155.   //--------------------------
  156.   public int getsequencenumber() {
  157.     return(SequenceNumber);
  158.   }
  159.  
  160.   //--------------------------
  161.   //getpayloadtype
  162.   //--------------------------
  163.   public int getpayloadtype() {
  164.     return(PayloadType);
  165.   }
  166.  
  167.  
  168.   //--------------------------
  169.   //print headers without the SSRC
  170.   //--------------------------
  171.   public void printheader()
  172.   {
  173.     //TO DO: uncomment
  174.     /*
  175.     for (int i=0; i < (HEADER_SIZE-4); i++)
  176.       {
  177.     for (int j = 7; j>=0 ; j--)
  178.       if (((1<<j) & header[i] ) != 0)
  179.         System.out.print("1");
  180.     else
  181.       System.out.print("0");
  182.     System.out.print(" ");
  183.       }
  184.  
  185.     System.out.println();
  186.     */
  187.   }
  188.  
  189.   //return the unsigned value of 8-bit integer nb
  190.   static int unsigned_int(int nb) {
  191.     if (nb >= 0)
  192.       return(nb);
  193.     else
  194.       return(256+nb);
  195.   }
  196.  
  197. }