private int fill(int offset,int length) throws IOException {

		int sum = 0, len;

		while (sum<length) {
			len = is.read(buffer, offset+sum, length-sum);
			if (len<0) {
				throw new IOException("End of stream");
			}
			else sum+=len;
		}

		return sum;

	}
RFC 4629.

  H.263 Streaming over RTP.
  
  Must be fed with an InputStream containing H.263 frames.
  The stream must start with mpeg4 or 3gpp header, it will be skipped.
src/net/majorkernelpanic/streaming/rtp/H263Packetizer.java