=head1 NAME

Net::SIP::DTMF - DTMF RTP packet generating and extracting

=head1 SYNOPSIS

  use Net::SIP::DTMF;
  my $sub = dtmf_generator(
    11,                  # event '#'
	100,                 # duration 100ms
	rfc2833_type => 101, # RTP type 101 for telephone-event/8000
	# audio_type => 0,   # RTP type 0 for PCMU/8000
  );
  while (...) {
  	my @pkt = $sub->($sequence,$timestamp,$srcid);
	last if ! @pkt;        # dtmf done
	next if $buf[0] eq ''; # more coming, but no data this time (pause)
	.. send @pkts ...
  }


  use Net::SIP::DTMF;
  my $sub = dtmf_extractor(
	rfc2833_type => 101, # RTP type 101 for telephone-event/8000
	audio_type => 0,     # RTP type 0 for PCMU/8000
  );
  while (...) {
  	if ( my ($event,$duration,$type) = $sub->($packet)) {
	  # event received
	  ...
	}
  }

=head1 DESCRIPTION

This package provides functions for generating RTP packets containing DTMF
events or extracting DTMF events from RTP packets. 

=head1 FUNCTIONS

=over 4

=item dtmf_generator ( EVENT, DURATION, %ARGS )

Generates a function which is used to generate packets for the given EVENT.

EVENT is the event numer (0..15) or undef if it should just generate silence or
pause. DURATION is the time for the event in ms. ARGS contain information how
the event should be packed: either as RFC2833 RTP event or as RTP audio
PCMU/8000.
%ARGS can be

=over 8

=item rfc2833_type => rtp_type

Gives the RTP payload type number for rfc2833 RTP events (telephone-event/8000). 
If not given will try B<audio_type> instead.

=item audio_type => rtp_type

Gives the RTP payload type number for PCMU/8000.
If not given and no B<rfc2833_type> given it will croak.

=item volume => volume

Sets the volume for RTP event according to rfc2833.

=back

The generated function should then be called with SEQUENCE,TIMESTAMP,SRCID to
generate the RTP packets and will return @RTP_PACKETS, with

=over 8

=item () - DTMF event is finished

=item $RTP_PACKETS[0] eq '' - no RTP packet for this call (pause)

=item @RTP_PACKETS - RTP packets which can be send to the peer

=back

=item dtmf_extractor ( %ARGS )

Generates a function which is used to extract DTMF events.
Keys B<rfc2833_type> and B<audio_type> have the same meaning as in
B<generate_dtmf>. It will only attempt to extract DTMF events from rfc2833 RTP
events or audio if the relevant rtp_type is given.

The function will be called with the RTP packet as the only argument and will
return () if no new events where found or (EVENT,DURATION,TYPE) if an event 
finished, where DURATION is the duration in ms and TYPE is audio|rfc2833.

For performance reasons it is best to use only rfc2833 if the peer supports it.

=back


