On 01/25/2011 05:48 PM, Dietfrid Mali wrote:
The problem with e.g. G.726 is that Wireshark gives those packets RTP
type 102 which afaik is an error code ("unknown encoding").
No, that's your RTP endpoint configured to label these as such. RFC 3550 says:
"A profile MAY specify a default static mapping of payload type codes to payload
formats. Additional payload type codes MAY be defined dynamically through
non-RTP means (see Section 3)."
RFC 1890/RFC 3551 defines the "RTP Profile for Audio and Video Conferences with
Minimal Control", which lists several static payload types. The old RFC lists
G.721 (aka G.726-32), while the new one dropped that one and added references to
G.726 at various bit rate, with a dynamic payload type.
RFC 3550 says in Section 3: "Non-RTP means: Protocols and mechanisms that may be
needed in addition to RTP to provide a usable service. In particular, ..., and
define dynamic mappings between RTP payload type values and the payload formats
they represent for formats that do not have a predefined payload type value."
with reference to Session Description Protocol (SDP)
So, payload type 102 is a dynamic payload type which has to be given meaning
(through SDP for instance) within the session. In your case Wireshark didn't
pick that up from the trace, hence cannot give you the proper interpretation of
that payload type within that session.
I would need to know where and how Wireshark maps dynamic payload types
(negotiated via SDP) to internal static ones. Above that RFC3551 notes that
static G.726 payload types are obsolete, and afaik there aren't even
(obsolete) static payload types for all G.726 variants, so Wireshark
would need to
take care of that by using some (more or less arbitrary) internal static
type numbers.
Yep, that is done by the SDP dissector. It tries to interpret the SDP offer
(should be the answer, but that a whole other story) and create conversations
(see doc/README.developer, section 2.2) for the RTP dissector, feeding it
dynamic payload type information it has learned from the media attributes.
The RTP dissector does then the heavy lifting on the RTP packets, based on the
information feed in by the SDP dissector.
I will do my best to provide a patch once I have fully integrated all
codecs (currently only G.726-32 has been implemented as proof of
concept, but since
this is working adding more is no big deal).
Just one to get started is fine. Does it integrate into codecs/ directory
besides G711a and G711u (and G729 and G723, if you have them)?
Getting G.726 to work was a bit of a pain btw because of the weird frame
sync calculation in rtp_player.c::play_channels() as this function seems to
assume 1:1 relationships of decoder input and output stream sizes and
thus simply halves the decoder output batch sizes to determine whether
frames
are properly sync'd. This doesn't work for compressed audio. To
compensate, my decodeG726_32() function doubles the number of bytes returned
(as it has a 1:2 relationship of input and output buffer sizes). Before
it did that, lots of silence frames were inserted and half of the audio
data was
dropped by the player.
I'm no sure if I understand you correctly. Working with these decode functions
there is an input buffer with its length as input, and two output parameters,
being the output buffer and it a pointer to store its size. This size of the
output buffer has to be set, by the decoder, to the number of samples in output
buffer. That should be enough, see for instance rtp_player.c:decode_rtp_packet()
the handling of G.279 and G.723.
Be aware that you have to store 16 bit linear samples in the output buffer,
maybe that's your factor 2?
Thanks,
Jaap
Dietfrid
> From: jaap.keuter@xxxxxxxxx
> Date: Tue, 25 Jan 2011 16:54:25 +0100
> To: wireshark-dev@xxxxxxxxxxxxx
> Subject: Re: [Wireshark-dev] G.722 and G.726 decoders for Wireshark
>
> Hi,
>
> That would be interesting. Can you put the code in a patch on bugzilla?
>
> Can't work on it right now, but would be nice to have.
>
> btw: their are already static RTP types assigned for both codecs. The
dynamic types should come in through protocols like SDP, or a dissector
preference.
>
> Thanks,
> Jaap
>
> Send from my iPhone
>
> On 25 jan. 2011, at 16:07, Dietfrid Mali <karx11erx@xxxxxxxxxxx> wrote:
>
> > Hi,
> >
> > using spandsp, I have added G.722 and G.726 decoders to Wireshark.
> >
> > Currently this is a bit of a hack job, particularly regarding
inclusion of the spandsp lib, and I could need a bit help to properly
integrate it into Wireshark's automake hell (configure.in).
> >
> > There also isn't a proper Wireshark signature for that RTP type (I
am simply reacting to RTP type 102, which actually is an error code), so
some help getting this straight and introducing proper codec types would
be appreciated, too.
> >
> >
> >
