I had the exact same question a few months ago. It has to be scripted and done via ESL as it is not supported natively by FS. If it can help, you can always bridge to a loopback/wait channel. 
In my scenario I wanted FS to continue dialplan execution while a ringback is played to the caller.

E
On May 31, 2016, at 3:49 PM, Dmitry Sytchev <kbdfck@gmail.com> wrote:

Maybe there is also possibility  to start background MOH when there is
no media on channel?

2016-05-31 14:57 GMT+03:00 Dmitry Sytchev <kbdfck@gmail.com>:
Hi all!

I'd like to resolve some unclear ringback behavior in early media
mode. I'm trying to implement ringback while no bridge active.
A calls FS, FS does something, then searching for B and bridges A to B.

I'd like to start playing custom ringback immediately after call from
A gets into FS, not when we start bridge to B.

I'm doing something like that:

<action application="set" data="ringback=%(2000, 4000, 440.0, 480.0)"/>
<action application="set" data="instant_ringback=true"/>
<action application="set" data="bridge_early_media=true"/>
<action application="pre_answer"/>
<action application="sleep" data="10000"/>
...
<action application="bridge" data="some bridge data"/>

There is no ringback to A in such scenario until bridge is called in
further dialplan processing. I've tried all combinations of
ignore/bridge early media, but with no luck. Pre_answer can be called
directly or by FS when call is recorded, with no difference. There is
a wiki page that recommends usage of ring_ready:

https://freeswitch.org/confluence/display/FREESWITCH/mod_dptools%3A+ring_ready

ring_ready works, but it can give only Ringing to calling side, so  I
can't pass custom RBT to calling party. It would be enough for me, but
once somebody calls pre_answer, no early media is passed until bridge
attempt.

What can be done to resolve this? Thanks in advance.







--
Best regards,

Dmitry Sytchev,
IT Engineer



-- 
Best regards,

Dmitry Sytchev,
IT Engineer

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