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

["Bernd Brantner" <brabell@xxxxxx>]

Anders,

here a snipped from RFC 3267 - RTP Payload Format for AMR and AMR-WB:

<snip>

   The AMR codec is a multi-mode codec that supports 8 narrow band
   speech encoding modes with bit rates between 4.75 and 12.2 kbps.  The
   sampling frequency used in AMR is 8000 Hz and the speech encoding is
   performed on 20 ms speech frames.  Therefore, each encoded AMR speech
   frame represents 160 samples of the original speech.

<snip>

      maxptime:  The maximum amount of media which can be encapsulated
               in a payload packet, expressed as time in milliseconds.
               The time is calculated as the sum of the time the media
               present in the packet represents.  The time SHOULD be a
               multiple of the frame size.  If this parameter is not
               present, the sender MAY encapsulate any number of speech
               frames into one RTP packet.

<end>

and from RFC 2327 - SDP: Session Description Protocol
   a=ptime:<packet time>
       This gives the length of time in milliseconds represented by the
       media in a packet. This is probably only meaningful for audio
       data.  It should not be necessary to know ptime to decode RTP or
       vat audio, and it is intended as a recommendation for the
       encoding/packetisation of audio.  It is a media attribute, and is
       not dependent on charset.

ptime should be 20ms for AMR and maxptime can be removed from the SDP file,
am I right?

Still the same problem with the short twich sound.

Bernd


> Hi,
> Regarding "108" it is a dynamic payload type ( 96 - 127 )what this payload
> type will be is
> "signaled" between the "server" and "host" in your perticular case 108
> "is" AMR
> as quicktime does not know of the signaling you must "tell" it by the SDP
> data.
> > > 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
> m=audio 49120 RTP/AVP 97 Tells it that m(edia) is araving at port 49120
> format is RTP/AVP
> a=rtpmap:97 AMR/8000/1 Tells it ( check the SDP RFC
> http://www.ietf.org/rfc/rfc2327.txt?number=2327 and
> http://www.iana.org/assignments/rtp-parameters ).
>  .../AMR/8000 where 8000 is 8khz
> perhaps you should change this to 4750 ? 
> Best regards
> Anders
> 
> -----Original Message-----
> From: ethereal-users-bounces@xxxxxxxxxxxx
> [mailto:ethereal-users-bounces@xxxxxxxxxxxx]On Behalf Of Bernd Brantner
> Sent: den 4 augusti 2004 15:41
> To: ethereal-users@xxxxxxxxxxxx
> Subject: RE: [Ethereal-users] Replay audio from RTP with AMR payload 
> 
> 
> 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
> > 
> > _______________________________________________
> > Ethereal-users mailing list
> > Ethereal-users@xxxxxxxxxxxx
> > http://www.ethereal.com/mailman/listinfo/ethereal-users
> > 
> > 
> 
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