[Freeswitch-dev] Questions about read_frame and write_frame events

[Anthony Minessale]

yes you must return a frame marked SFF_CNG rather than a NULL frame.

The TFLAG flags are all arbitrary, you can get rid of all of them if you
wish they are just an example of how those modules communicate internally.
Sometimes they were used for the host technology to have a way to mark the
channel so the call should die but you may get the same effect by just
hanging up the channel since the core now does a lot of this and may never
let your read func even be called.


On Mon, Nov 9, 2009 at 3:54 AM, Alex To <tonhudung at gmail.com> wrote:

>  Thank you very much Mathieu
>
>
>
> So if TFLAG_IO is not set, read_frame will return immediately and *frame is
> NULL ? Is it a normal behavior if the call is terminated when a NULL frame
> is returned ?
>
>
>
> Coz when I return a NULL frame, the call is terminated. So now my
> understanding is that if my endpoint buffer is empty, I need to return a
> silence frame to the other end, right?
>
>
>
> Thank again Mathieu for your quick reply, that helps a lot J.
>
>
>
> Regards
>
>
>
> Alex To
>
>
>
> *From:* freeswitch-dev-bounces at lists.freeswitch.org [mailto:
> freeswitch-dev-bounces at lists.freeswitch.org] *On Behalf Of *Mathieu Rene
> *Sent:* Monday, November 09, 2009 2:54 AM
> *To:* freeswitch-dev at lists.freeswitch.org
> *Subject:* Re: [Freeswitch-dev] Questions about read_frame and write_frame
> events
>
>
>
> Hi,
>
>
>
> See answers inline.
>
>
>
> Mathieu Rene
>
> Avant-Garde Solutions Inc
>
> Office: + 1 (514) 664-1044 x100
>
> Cell: +1 (514) 664-1044 x200
>
> mrene at avgs.ca
>
>
>
>
>
>
>
>
>
> On 8-Nov-09, at 4:21 AM, Alex To wrote:
>
>
>
>   Hi,
>
>
>
> I am getting stuck on read_frame and write_frame in my custom endpoint.
> Would someone shed some lights on how it works?
>
>
>
> My questions about read_frame, write_frame after reading mod_iax,
> mod_portaudio and mod_skyiax are:
>
>
>
> 1.       Is it correct that I need to check a flag (for e.g TFLAG_HUP)  of
> the private object at the beginning of the event to determine whether I
> should continue reading audio or just return. The flag TFLAG_HUP is set when
> a hangup or kill channel event is detected.
>
> Thats what TFLAG_IO is for, clear the flag the read_frame functions should
> return immediately.
>
> If you catch TFLAG_BREAK, on the other side, you should clear it and return
> a comfort noise frame ( cng )
>
>   2.       Read_frame is called on an interval (how frequently is the
> interval ? how do I determine that?) to read audio from my endpoint.
>
> It depends on the codec you are using, if you are using 20 packetization
> time, it'll be called every 20ms.
>
>   3.       What is TFLAG_IO normally used for ?
>
> See point 1
>
>   4.       What is the label “cng” is all about ? May I know what “cng”
> stands for and how it is used?
>
> CNG stands for Comfort Noise Generation, whenever read_frame jumps there,
> it returns a frame of silence. It it first initialized on private_t since
> its pointless to re-allocate empty frames.
>
>   5.       What if read_frame is called while my end point is not ready to
> send any audio yet?
>
> That's why you set TFLAG_IO whenever you are ready. Also note that it wont
> be called until you either pre_answer (go in early media) or answer the
> channel.
>
> When a call is made, switch_ivr_originate() doesn't return until your
> endpoint is ready to exchange audio.
>
>   6.       What is the tech_pvt->cng_frame is used for? I notice that the
> *frame is set to tech_pvt->cng_frame if the label “cng” is reached.
>
> See point 4.
>
>
>
> Thank you very much for even reading my questions. I tried to look for
> documents that explains clearly the above questions but so far no luck.
> Until now I still don’t have a clear understanding about these 2 events yet.
>
>
>
> Best Regards
>
>
>
> Alex To
>
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-- 
Anthony Minessale II

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