Tamar Nemet and Matt Adams asked:
I captured RTP packets with the ethereal tool on my PC. How can I hear
the RTP stream using the ethreal or any other tool?
>How do I filter and save the voice payload so that a media player can play the
>message back?
We don't usually filter because the RTP analysis part is used to select which
port you're going to hear, so just capture everything. Once the file is
captured, select one RTP packet from either UDP (ie, RTP) port used by your
call. From the Analyze menu, select "Decode As". In this dialog box, make sure
"decode" is ticked. Choose "both" from the UDP ports menu. Select RTP from the
list of protocols.
Now, from Statistics menu select "RTP" and then "Stream Analysis." Click on
"Save Payload", and in that dialog box make sure "both" is checked, then give it
a filename and save it away. This creates a .au type of file.
We use CoolEdit to see the waveform and do spectral analysis on the audio file,
but I think it plays in some default Windows player as well.
If anyone knows a better way, please post...
Now, a question for the group: when using a payload type that doesn't conform to
one of the known values (ie, 0 for G711ulaw, 8 for G711alaw, or 18 for G729
etc...) ethereal will not decode the stream. We use a negotiated value for a
clear-channel data stream and in order to hear it, I use a perl script (or a
regexp in xemacs in binary mode!) to replace the payload type byte in all the
RTP packets with a 00. This works fine, but it would be nice if ethereal had a
way to specify the pt used for x-ccd (or even if you just wanted to "force" it
to decode anyway). I just started using ethereal, so am not terribly familiar
with it yet - perhaps this functionality is in there somewhere already?
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