Wireshark · Ethereal-users: RE: [Ethereal-users] Replay audio from RTP with AMR payload

["Bernd Brantner" <brabell@xxxxxx>]

All,

replacing 97 with 108 makes a difference, thanks (I thought 108 is just the
code for unrecognised payload. Now Quicktime recognises AMR Narrowband,
Mono, 8000Hz. And it starts to play "twitch" sounds aka "dolphin sounds" for
half a second (but not for the whole length of play) when I use rtpplay with
option -T; and for the whole length without -T.

RTP should be fine as it can be replayed by rtpplay, timestamp is also
incrementing. This sound seems to indicate an incorrect decoding. Any
further ideas?

Regards,
Bernd


> Subject: RE: [Ethereal-users] Replay audio from RTP with AMR payload 
> From: "Anders Broman (AL/EAB)" <anders.broman@xxxxxxxxxxxx> 
> Date: Tue, 3 Aug 2004 17:02:06 +0200 
> 
>
--------------------------------------------------------------------------------
> 
> Hi,
> I think the problem may be the SDP file, shouldn't 97 be replaced with 108
in this case?
>  As 108 is the payload type in this particular case and was 97 in the
example given by Martin ?.
> Best regards
> Anders
> 
> -----Original Message-----
> From: ethereal-users-bounces@xxxxxxxxxxxx
> [mailto:ethereal-users-bounces@xxxxxxxxxxxx]On Behalf Of Lars Ruoff
> Sent: den 3 augusti 2004 16:26
> To: Ethereal user support
> Subject: Re: [Ethereal-users] Replay audio from RTP with AMR payload
> 
> 
> Hi,
> 
> > I've got a problem extracting the audio from RTP packets. I followed the
> > excellent tips given by Martin Regner on how to deal with not supported
> > codecs (save full RTP packets, use rtpplay and quicktime to replay and
> > listen to audio) asdescribed here
> > (http://www.ethereal.com/lists/ethereal-users/200401/msg00264.html).
> >
> > I captured the audio stream (AMR 4.75) from a mobile phone (not GSM
voice
> > but VoIP done with a PushtoTalk Java client on the phone) and was able
to
> > convert the log file to the PCAP format. I can open it without any
problem
> > in Ethereal, decode the appropriate UDP packets as RTP, however the
> payload
> > is not recognised (Payload type=Unknown (108)).
> 
> AMR is a dynamic payload type, which aren't handled by Ethereal to my
> knowledge (?).
> However, exporting the RTP packets via "Save as rtpdump" should still
work!
> 
> >
> > I prepared an SDP file, which instructs Quicktime for my AMR 4.75 stream
I
> > send with rtpplay but Quicktime doesn't understand what it's getting.
> Could
> > it be that rtpplay doesn't deal with the payload properly?
> 
> No, rtpplay doesnt even know about payload. It dumbly replays RTP packets,
> whatever the payload might be.
> There might however be an issue with your version of rtpplay using a
> different file format than Ethereal (unfortunately, rtpdump file format
has
> not been specified in a compiler-independent way). To test: let rtpplay
> replay the packets to some dummy IP, then capture those packets again with
> Etherel and see if they're still the same as the original ones.
> 
> > Or that Quicktime
> > doesn't support AMR properly?
> 
> Most likely. However i dont know Quicktime myself.
> 
> > Or that my log file is not properly converted
> > to PCAP format? But I can open it and decode RTP, so the payload should
be
> > ok, right?
> 
> Yes. most likely. Check if the other RTP fields make sense.
> (SSRC stays the same, timestamps increment etc.)
> 
> >
> > The media and attributes section of my SDP file:
> > m=audio 49120 RTP/AVP 97
> > a=rtpmap:97 AMR/8000/1
> > a=fmtp:97 mode-set=0,1
> > a=ptime:20
> > a=maxptime:20
> >
> > Any help is highly appreciated!
> >
> > Regards,
> > Bernd
> 
> Martin might have additional info on the Quicktime specific issues.
> 
> regards,
> Lars Ruoff
> 
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> 
> 

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