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Re: [Linphone-developers] ortp: processing incoming stream

From: Petr Kuba
Subject: Re: [Linphone-developers] ortp: processing incoming stream
Date: Fri, 27 Nov 2009 17:36:00 +0100
User-agent: Mozilla/5.0 (Windows; U; Windows NT 5.2; en-US; rv: Gecko/20070111 SeaMonkey/1.1


Simon Morlat wrote:
Ok I understand.
The correct way of setting off the jitter buffer is to do rtp_session_enable_jitter_buffer(session,FALSE);
In this mode you'll get all packets regardless that they are late or

Thanks, I'll test this.

About SSID: don't you meant SSRC ? Yes you should expect a random value.
How did you see this 0x29 value ? gdb ? wireshark ?

Yes, of course I meant SSRC, sorry for that typo. I saw the value in wireshark - and I see it there always under windows. I'm not sure about Linux at this moment. May be this is some problem with random generator. I'll try to walk through the code and let you know.



Le vendredi 27 novembre 2009 à 15:39 +0100, Petr Kuba a écrit :
Hi Simon,

Thanks for your response.

I've tested your approach and it works well with low jitter of an incoming stream and adaptive jitter enabled.

However, if I disable the jitter buffer I miss quite a lot of packets (jitter is up to 10ms) and I have to use rtp_getq_permissive(). Then I receive all the packets.

I'm handling situations where I just forward packets from one RTP stream to another and I don't want to delay the packet by using jitter buffer. And I don't want to miss packets event if they are e.g. 40ms late.

So, I have several questions:

1) What is the correct way to receive all the packets without modifying ORTP source code if I don't use jitter buffer? It would be nice to obtain a packet immediately after it is delivered.

2) I'm not sure how to correctly configure jitter buffer. What is the correct way to switch the jitter buffer off? Calling rtp_session_set_jitter_compensation(s, 0) or calling nothing?

3) When switching the jitter buffer on do I have to call rtp_session_set_jitter_compensation() before rtp_session_enable_adaptive_jitter_compensation()? And what happens if I call rtp_session_set_jitter_compensation() after rtp_session_enable_adaptive_jitter_compensation()? Does it make sense to combine these two methods?

4) I've noticed that all my outgoing stream have SSID=0x29. I don't call
rtp_session_set_ssrc() so I would expect it to have a random value. Do you have any idea what is wrong?


Simon Morlat wrote:
Hi Petr,

Your application should increment the timestamp using its theoritical
value (ex: 10 ms if your application is supposed to wake up and do
processing every 10 ms), no matter if it is a bit late compared to real
time or not.
The important is only that on the long term, the timestamp and the time
elapsed are equivalent (no drift).


Le vendredi 20 novembre 2009 à 14:43 +0100, Petr Kuba a écrit :

I'm experiencing the following problem:

Since the timer we use for calling rtp_session_recvm_with_ts() is not 100% precise (mainly in windows) it happens quite often that the time between two calls of rtp_session_recvm_with_ts() is (a little bit) longer that 20ms. Then it is quite often that there are already two packets older than current timestamp in the ortp queue.

However, rtp_session_recvm_with_ts() calls rtp_getq() which returns only the last packet and discards all older packets. I believe that this is not good idea when we are only few ms late.

In my case it would be better to call rtp_getq_permissive() instead of rtp_getq() not to miss any packets.

What do you think? Do I miss any important idea of this algorithm? What is the reason for discarding a packet that we wouldn't discard e.g. just 1ms earlier?


   Petr Kuba, Project Manager
   OptimSys, s.r.o
   Tel: +420 541 143 065
   Fax: +420 541 143 066

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