[Freeswitch-users] RTP timestamps jumping backwards

Richard Brady rnbrady at gmail.com
Fri Mar 28 16:43:03 MSK 2014


Do you mean the CHANGE_SSRC_ON_MARKER setting?

I don't think that's the way to address it. Marker aside, I'd like the SSRC
to change when switching from locally generated to relayed media, but I
guess that would also cause the "problems with some devices" of which you
speak.

If you mean rtp-rewrite-timestamps then I'm divided.

What I can't work out is why the SSRC isn't changing when the source
changes. My reading of the code says it should be.

Richard

On 28 March 2014 13:11, Peter Olsson <peter at olssononline.se> wrote:

> I believe that setting was the other way around in my original patch (to
> use this by default). However, even if it sounds like it should be more
> compliant, it caused problems with some devices - that's why it ended up
> like this. It was some time ago - so I don't remember every detail though.
>
>
> 2014-03-28 13:39 GMT+01:00 Richard Brady <rnbrady at gmail.com>:
>
> Thanks Peter
>>
>> That's really useful. I opted for rtp-rewrite-timestamps but had missed
>> that one and will try it next if I don't see an improvement. There's also
>> RTP_BUG_SEND_LINEAR_TIMESTAMPS.
>>
>> I'm quite confident I can work around the issue but would like to make
>> sure that if there is an RFC non-compliance in default FS we get it
>> resolved for the benefit of others.
>>
>> My understanding:
>>
>> The marker bit makes it ok to jump the timestamp for silence suppression
>> / discontinuous transmission etc.
>>
>> BUT the marker bit doesn't make it ok to change the timestamp SOURCE (and
>> jump the timestamp backwards for example). In that case the SSRC MUST
>> change too.
>>
>> Regards,
>> Richard
>>
>> On 28 March 2014 11:08, Peter Olsson <peter at olssononline.se> wrote:
>>
>>> There is actually a setting to force new SSRC in a condition like that.
>>>
>>> Internally it's called RTP_BUG_CHANGE_SSRC_ON_MARKER. If I remember
>>> correctly it should be set in the sofia profile config:
>>>
>>> <param name="auto-rtp-bugs" data="CHANGE_SSRC_ON_MARKER"/>
>>>
>>> Try that out and see if it helps.
>>>
>>> /Peter
>>>
>>>
>>> 2014-03-28 11:37 GMT+01:00 Richard Brady <rnbrady at gmail.com>:
>>>
>>>>  Hi Anthony and team
>>>>
>>>> I have a situation where the timestamp in a RTP stream generated by FS
>>>> jumps backwards. Version 1.2.22.
>>>>
>>>> It seems the cause of this is that media from the A leg starts late. So
>>>> in the meantime we start generating media on the B leg with our own
>>>> timestamp.
>>>>
>>>> Then media starts arriving on the A leg so we relay it and we start
>>>> using that timestamp instead of our own.
>>>>
>>>> FS sets the marker bit when this happens but I'm not sure this makes it
>>>> OK to turn back the timestamp. I think we should actually be using a new
>>>> SSRC.
>>>>
>>>> Any thoughts? (happy to raise a Jira ticket and verify in master).
>>>>
>>>> Richard
>>>>
>>>> --
>>>> Richard Brady
>>>> M: +44 (0)7771 623 348
>>>> T:  +44 (0)20 8144 8160
>>>> E: rnbrady at gmail.com
>>>>
>>>>
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>
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