rtpengine: document play_dtmf() command

src/modules/rtpengine/doc/rtpengine_admin.xml

@@ -2888,6 +2888,45 @@ stop_media("from-tag=5yqaeriguhxcikxj");
 		</example>
 	</section>
 
+	<section id="rtpengine.f.play_dtmf">
+		<title>
+		<function moreinfo="none">play_dtmf([flags])</function>
+		</title>
+		<para>
+		Injects a DTMF event into the media stream. Depending on which codecs were
+		negotiated, this either injects an RFC 2833/4733 DTMF event, or an in-band PCM
+		DTMF tone into the audio stream. The flag <quote>inject DTMF</quote> must have
+		been present in both offer and answer messages when the call was established,
+		which forces all audio to go through rtpengine's transcoding engine.
+		</para>
+		<para>
+		Usage is similar to <quote>play_media</quote> with the following exceptions.
+		The selected party is not the party that will receive the DTMF event, but rather
+		the party which is generating the event. This is to support DTMF
+		events that are carried in &sip; INFO messages. Instead of specifying a media file,
+		a DTMF event code must be specified, as well as optionally a duration and the volume.
+		The <quote>code</quote> can be a number 0 through 15, or a DTMF digit (0-9, A-D, *, #).
+		The <quote>duration</quote> is specified in milliseconds and defaults to 250, within
+		a range of 100-5000. The <quote>volume</quote> is specified in absolute decibels, with
+		a default of -8 db.
+		</para>
+		<para>
+		Multiple consecutive DTMF events can be queued up by calling this function multiple
+		times consecutively. Rtpengine will play out the DTMF events in sequence, separated
+		by a default pause of 100 ms. An alternative pause length can be given through the
+		<quote>pause</quote> option, between 100 and 5000 ms.
+		</para>
+		<example>
+		<title><function>play_dtmf</function> usage</title>
+		<programlisting format="linespecific">
+...
+play_dtmf("from-tag=5yqaeriguhxcikxj code=#");
+play_dtmf("code=1 volume=5 duration=300 pause=150");
+...
+		</programlisting>
+		</example>
+	</section>
+
 
 	</section>