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@lists.freeswitch.org [mailto:freeswitch-dev-bounces@lists.freeswitch.org] On Behalf Of Mathieu Rene
Sent: Monday, November 09, 2009 2:54 AM
To: freeswitch-dev@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

 

 

 

 

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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