Jay Mc Grath wrote:
>How can I passively capture a Voice over IP steam and transform it to a
>.wav media file? Any suggestions?
Is the VOIP stream an RTP stream?
Ethereal 0.9.11 has a functionality RTP Analysis that can be used to convert RTP packets
to ".au" sound-file.
There are a lot of programs that can convert from .au to .wav if you really
need to use the .wav format but actually you should be able to play the .au file direct, I assume.
Currently this only works for G.711 (PCMU and PCMA).
If the RTP packets are not shown as RTP you first have to select one of the packets and
use the "Tools/Decode As..." menu item and select that the packets shall be decoded as RTP.
http://www.ethereal.com/faq.html#q5.21
Then you mark one of the RTP packets and use the "Tools/Statistics/RTP Analysis..." menu item to
obtain some statistics about delay and jitter.
If the codec is G.711 (PCMU/PCMA) you should be able to use the "Save voice data as..." button
in the RTP Analysis window.
If you want to experiment with this and don't have any RTP captures available you can find
one attached to the following message (mytest.pcap) and another in the linked message
from Miha Jemec:
http://www.ethereal.com/lists/ethereal-users/200303/msg00092.html
There are some more RTP sample captures in libpcap format available on this webpage:
http://netgroup-serv.polito.it/avican/examples/index.htm
Some RTP packets in these captures are G.711 PCM U-law (audio) and some are H.261 (video).
You can currently only save the G.711 audio packets to file from the RTP Analysis.
I will try to add support to the RTP Analysis for storing RTP packets in rtpdump-format.
Then it will be possible to save any audio or video codec, and use e.g. rtpplay to replay the media stream towards JMF/JMPlayer, QuickTime Player or similar (depending on what codecs these program supports).
I'm already today replaying RTP streams (H.261 video, H.263 video, G.723.1 audio, GSM audio, ... )
by using another program that extracts RTP packets from capture file and saves the file in rtpdump-format.
