public Mp4TagByteField(Mp4FieldKey id,String value,int realDataLength) throws FieldDataInvalidException {
  super(id.getFieldName(),value);
  this.realDataLength=realDataLength;
  try {
    Long.parseLong(value);
  }
 catch (  NumberFormatException nfe) {
    throw new FieldDataInvalidException("Value of:" + value + " is invalid for field:"+ id);
  }
}

public Mp4TagByteField ( Mp4FieldKey id , String value , int realDataLength ) throws FieldDataInvalidException { super ( id . getFieldName ( ) , value ) ; this . realDataLength = realDataLength ; try { Long . parseLong ( value ) ; } catch ( NumberFormatException nfe ) { throw new FieldDataInvalidException ( "Value of:" + value + " is invalid for field:" + id ) ; } }
create new field with known length
