Hello there!
We work with a Windows application here that uses Openwengo libraries to
provide Voip services, and we are dealing with some packetization
problems where an offerer supports only 30ms packetization for iLBC codec.
Having a look on iLBC implementation on "phApi", I've noticed that
almost all codecs support only 20ms packetization which could maybe
became dynamic with use of just one parameter that isn't being applied
by now.
For iLBC at least, the packetization is configured on codec
initialization method "phcodec_t::encoder_init" which receives "NULL" by
now for a "void *" parameter.
The general idea is:
1- On the same way the "ptime" attribute was added to "eXosip_event"
struct, we could add a new field (maybe called "format_modifiers"), that
will hold a list of all "fmtp" attribute values collected from the media
negotiation.
For the negotiation below, for example, the result list will have the
items: "111 mode=30" and "101 0-16".
Media Description, name and address (m): audio 15738 RTP/AVP 111 101
Connection Information (c): IN IP4 200.221.10.68
Media Attribute (a): rtpmap:111 iLBC/8000
Media Attribute (a): fmtp:111 mode=30
Media Attribute (a): rtpmap:101 telephone-event/8000
Media Attribute (a): fmtp:101 0-16
Media Attribute (a): ptime:20
Media Attribute (a): maxptime:20
Media Attribute (a): direction:active
This data extraction could happen on "eXosip_get_sdp_media_info" method,
or inside method "eXosip_event_add_sdp_info", by a new method called
"eXosip_get_sdp_media_format_info", on the same way it's done with
"ptime" attribute.
I choose to put it inside method "eXosip_event_add_sdp_info" to avoid a
new change on method "eXosip_get_sdp_media_info" signature without a
good reason. Please point your options and objections about any details
of the approach like this one.
2- The second pass envolves the processing of the list of collected
attrubutes on a usefull field indicating the mode used by the codec. I
choose to make this task inside method "ph_call_media_start" with the
help of a new method called "eXosip_get_format_mode".
Here I'm with a pair of questions on mind that you guys can help me out:
1- Should I create a new field "mode" on "ph_mstream_param_s" struct on
the same way that happened with "ptime" (which will be interpreted as a
global configuration), or can I use the "mode" atrubute present on
"ipayloads" first element (that on my testes always have the selected
payload paramaters) ? 2- If I choose to store this info on a per-payload
basis (using "ipayloads" field), must I consider that "ipayloads" will
have more than one element and make a one-to-one analysis with
formatation and payload (this could seem a dumb question considering
that "ipayloads" is a array of 16 elements, but on my tests it always
have only one item assigned) ?
For now, I'm using "mode" field from "ipayloads" first element, but I
think maybe a new field should be created on "ph_mstream_param_s" struct
(on a global fashion) considering that, at least on my tests, generally
the streams envolved are just one (maybe on video this could be
different ??? ).
3- With the "mode" collected and available on "ph_mstream_param_s" (or
on one of "ipayloads" elements), it becomes easy to get this info on
method "ph_msession_audio_stream_hardstart" and pass it during encoder
and decoder initialization that for now receives always a "NULL" on it's
"void *" only parameter. Maybe a new struct could be created to pass the
required info to the encoder and decoder initialization methods.
On the same way the "mode" must be propagated to "phastream_t" created
on method "ph_msession_audio_stream_hardstart", so this field could be
used on "ph_astream_decoded_framesize_get" too to avoid conflicted
scenarios like the example above where "ptime" indicates 20ms and "mode"
indicates 30ms for packetization.
4- On each codec initialization, this info will be handled accordingly
to get the expected frame packetization. For now I'm proposing only to
change "iLBC" initialization considering that it's the only one we have
problems until now.
Does anyone see any problems with this approach ?
Is there any possibility of such maintenance being added to main Qutecom
codes ?
Thanks and best regards!
--
__At.,
_
*Technology and Quality on Information*
Mauro Sérgio Ferreira Brasil
Coordenador de Projetos e Analista de Sistemas
+ [EMAIL PROTECTED] <mailto:@tqi.com.br>
: www.tqi.com.br <http://www.tqi.com.br>
( + 55 (34)3291-1700
( + 55 (34)9971-2572
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