Re: [Linphone-developers] G722

[Simon Morlat]

Hi Vadim,

I think some small modifications like:

static int sender_set_session(MSFilter * f, void *arg)

{

SenderData *d = (SenderData *) f->data;

RtpSession *s = (RtpSession *) arg;

PayloadType *pt =

rtp_profile_get_payload(rtp_session_get_profile(s),

rtp_session_get_send_payload_type(s));

if (pt != NULL) {

if (strcasecmp(pt->mime_type,"g722")==0)

d->rate=8000;

else d->rate = pt->clock_rate;

} else {

ms_warning("Sending undefined payload type ?");

}

d->session = s;

return 0;

}

static int receiver_set_session(MSFilter * f, void *arg)

{

ReceiverData *d = (ReceiverData *) f->data;

RtpSession *s = (RtpSession *) arg;

PayloadType *pt = rtp_profile_get_payload(rtp_session_get_profile(s),

rtp_session_get_recv_payload_type

(s));

if (pt != NULL) {

if (strcasecmp(pt->mime_type,"g722")==0)

d->rate=8000;

else d->rate = pt->clock_rate;

} else {

ms_warning("Receiving undefined payload type ?");

}

d->session = s;

return 0;

}

Assuming the g722 encoder increments its timestamp by 160 each time it processes 320 samples of pcm data, this should work.

Do you agree ?

Simon

>

> The desire to keep stable ABI is very good reason to avoid changing

> payload type.

>

> However it seems that modifciations of of msrtp.c becomes somewhat more

> complicated than

> you think.

>

>

> First of all when sending (line 223 at msrtp.c) we need to do something

> like:

>

> / if (pt == g722_pt)

> timestamp /= 2;/

>

> Then when receiving, in addition fo 'reading' 8000 instead of 16000 from

> the payload descriptor we need to

> do something like in receiver_process:

>

> / while ((m = rtp_session_recvm_with_ts(d->session, timestamp)) !=

> NULL) {

> uint32_t pkttstamp = rtp_get_timestamp(m);

> int pt = rtp_get_payload_type(m);

>

> if (pt == g722_pt)

> pkttstamp *= 2;

>

> mblk_set_timestamp_info(m, pkttstamp);

> mblk_set_marker_info(m, rtp_get_markbit(m));

> mblk_set_payload_type(m, pt);

> rtp_get_payload(m,&m->b_rptr);

> ms_queue_put(f->outputs[0], m);

> }

> /

>

> Any comments?

>

> BTW the g722_pt could have different values for send and receive

> directions, but this

> is a general problem in mediastreamer --- even if oRtp is able to

> function with different profiles for each direction

> mediastreamer2 and linphone does not support it

>

> Thanks

> Vadim

>

> > Simon

> >

> > Le Wednesday 28 January 2009 19:30:56 Vadim Lebedev, vous avez écrit :

> >> Hello,

> >>

> >> We've a following interop problem with G722 codec:

> >>

> >> Because of historical reasons the relevant RTP RFC speicifies that

> >> when using G722 payload

> >> RTP TIMESTAMP should be incremented with 8KHZ frequency even if the

> >> REAL sampling rate

> >> is 16KHZ.

> >>

> >> As you understand msrtp.c filter is unable to handle this situation,

> >> so we've been thinking about possible enchancements.

> >>

> >> One idea that comes to mind is to add a 'rtp_rate' field to Payloadtype

> >> structure , and if it is non zero and different from sampling rate to

> >> compute adjustement (divider or multiplier) to rtp time stamp.

> >>

> >> Any comments on this approach?

> >>

> >>

> >> Thanks

> >> Vadim

> >>

> >>

> >>

> >> _______________________________________________

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