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