=head1 NAME

Net::SIP::SDP - Parsing and manipulation of SDP data for SIP

=head1 SYNOPSIS

  my $sdp = Net::SIP::SDP->new( sdp_string );
  my @media = $sdp->get_media;

=head1 DESCRIPTION

Net::SIP::SDP can parse and manipulate SDP data.

It's not a general purpose SDP class (like L<Net::SDP>) but
designed to work with SDP data contained in SIP packets
and for easy extraction and manipulation (for NAT etc)
of media information contained in the SDP.

The class is also designed for easy creation of SDP bodies
in the context of the rest of Net::SIP::*.

=head1 EXAMPLES

  # creation based on media data
  my $sdp = Net::SIP::SDP->new(
	{ addr => '192.168.0.1' },
	{ port => 2012, proto => 'RTP/AVP', media => 'audio', fmt => 0 },
	{ port => 2014, proto => 'RTP/AVP', media => 'video', fmt => 0 },
  );

  # parse from string
  my $sdp = Net::SIP::SDP->new( sdp_string );

  # extract all media data
  my @media = $sdp->get_media;

  # and replace them with new addr + port (for NAT)
  my @new_media,;
  foreach (@media) {
	my ($port,@socks) = create_rtp_sockets( '192.168.178.1', $_->{range} );
	push @new_media, [ '192.168.178.1', $port ];
	...
  }
  $sdp->replace_media_listen( @new_media );

=head1 CONSTRUCTOR

=over 4

=item new

Default constructor.
Depending on kind of arguments branches into B<new_from_string> or B<new_from_parts>.
See there.

=item new_from_string ( STRING )

Creates object from STRING containing the SDP data.
Raises an exception (e.g. die()) if SDP is invalid.

=item new_from_parts ( \%GLOBAL, @MEDIA )

Creates object from specification.
%GLOBAL describes the global keys, usually only a common C<addr> for all media but
any of the keys defined in L<RFC2327> can be used.

@MEDIA is a list of hash references, one hash for each media part. These hashes
can contain as keys the one-letter keys specified in L<RFC2327> and/or special
keys for constructing the 'c' and 'm' line:

=over 8

=item addr - The address, used in the 'c' line.

=item port -  The port number

=item range - Range of ports, for RTP/AVP defaults to 2, else 1

=item media - The media typ, e.g. 'audio','video',...

=item proto - Transport protocol, ususally 'RTP/AVP' or 'udp'

=back

If the SDP should contain multiple values for the same key in the same
media section on can specifiy the value for the key as a \@list instead
of a string (this is often the case for 'a' lines).

=back

=head1 METHODS

=over 4


=item as_string

Returns string representation for object.

=item content_type

Returns 'application/sdp'

=item get_media

Returns list of all media described in the SDP. If the caller expects
an array the result will be a list, otherwise a reference to a list.

Each element of the list is a hash with the following keys:

=over 8

=item addr - IP4/IP6 address for media

=item port - Start port

=item range - Range for ports

=item proto - Media proto, usually 'RTP/AVP' or 'udp'

=item media - Media typ, usually 'audio', 'video' or 'data'

=item fmt - Format info from media line as \@list, e.g C<< [ 0,10,5 ] >>.

=item lines - All lines from media description as \@list of [ key,value ].

=back

B<WARNING!> You should never manipulate the values you got from this function,
because this might affect the objects internals.

=item replace_media_listen ( NEW_MEDIA )

Replaces the exisisting media in the object with new media. Useful for NAT.

NEW_MEDIA is ether an array or a reference to an array. Each element in
the list consists of the new [ addr,port ] mapping for the matching media
entry.

The number of entries in the list should be the same as the number of media
entries in the object ( see B<get_media> ). If this is not the case it will
C<die()>.

=item name2int ( NAME, INDEX )

Returns the RTP payload id for NAME (e.g. "telephone-event/8000").
INDEX is the index into the list of media information, matching the list
returned from L<get_media>. INDEX can also be 'audio','video'.., which
will then lookup at the first matching entry in the media list.

=back