VOIP Sniffer

[wajdi]

hi all,

I must create a voip sniffer (to capture communication VOIP on the network) and then to convert them into audio format.
I succeeded in preparing a sniffer in C++ (by using the library winpcap) to:
1- capture network traffic
2-filtre UDP trafic
3-Read ethernet,ip and udp header.

But I do not know how to advance now how to convert this pacquet.
Please Help me.
(Sorry for my bad english)
Thank you a lot

[Edders]

The RTP header contains an ID. For some compression types this is a fixed ID, so when you have the ID you know what compression is used for the audio. Unfortunately there are also dynamic IDs that are only used for that session. To find out the type of compression ascociated with a dynamic ID you need to also have captured the original SIP/SDP communication that was used by the VOIP clients to setup the session.

After you found out the particular flavour of audio in the used in the RTP stream you can use the appropriate library to decode it to PCM audio and store it in a file.

PS - Please do not post the same question multiple times - opening one new thread should be enough to get your answer.

[logan]

In addition to what Edders said, there are numerous codecs out there like G.711, GSM, G.729, iLBC, Speex, etc. And you would need to know and understand all of them.

[wajdi]

Thank you so much for the answer.

I khnow that the codec is G 729 A !
where can i find the appropriate library to decode it ?
Can I use " OpenH323" ? if yes,where can i found a good tutorial about this library ?

Thank you