Creating an Audio File from a Pcap File Using Tshark

Learn how to extract audio data from Pcap files using `Tshark` with simple commands and tools for your VoIP and RTP analysis.
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How to Create an Audio File from a Pcap File with Tshark

Have you ever faced the challenge of extracting audio data from a Pcap file? If you're dealing with VoIP recordings and need to convert them into an audio format for analysis, you've come to the right place! While Wireshark provides a user-friendly interface for such tasks, using the command-line tool Tshark can be just as powerful and efficient. In this guide, we will go through the step-by-step process of extracting audio data from a Pcap file using Tshark.

What You Will Need

To achieve this, you will require:

Linux Operating System (Linux): The commands provided are optimized for Linux environments.

Tshark: An advanced command-line version of Wireshark.

Shell Tools: Tools like tr, xxd, and possibly sox or ffmpeg for audio conversion.

Pcap File: Your recorded VoIP phone conversation stored in a Pcap file format.

Step-by-Step Guide

1. Extracting RTP Packets

First, we need to extract the RTP packets from the Pcap file. If your Pcap contains audio from a single call, run the following command in your terminal:

[[See Video to Reveal this Text or Code Snippet]]

This command does the following:

-n disables name resolution.

-r call.pcap specifies the Pcap file to read.

-2 loads the second pass to filter for RTP packets.

-R rtp filters for RTP packets.

-T fields -e rtp.payload extracts only RTP payload fields.

tr and xxd process the output to create the call.rtp file.

2. Extracting Multiple RTP Streams

If the Pcap file contains multiple calls, you'll need to filter the RTP streams by their source or destination IP addresses, or by their SSRC (Synchronization Source Identifier). For example, if the SSRC is 0x7f029328, the command would look like:

[[See Video to Reveal this Text or Code Snippet]]

Here, you customize the filtering based on the specifics of your Pcap file.

3. Converting RTP to Audio Format

Once you have the call.rtp file, the next step is to convert it into a standard audio format, such as WAV. Depending on the codec used during the call, you can use either sox or ffmpeg:

Using Sox

For calls encoded with G711u (PCMU) and a sample rate of 8000 Hz, the command is:

[[See Video to Reveal this Text or Code Snippet]]

Using FFmpeg

For different codecs such as G729 or G722, you can employ ffmpeg. For example, for G722 with a sample rate of 16000 Hz, use the following:

[[See Video to Reveal this Text or Code Snippet]]

Conclusion

Extracting audio files from Pcap files using Tshark can seem daunting initially, but with the right commands and tools, it becomes a manageable task. Remember to select the appropriate audio conversion tool based on the codec used in your VoIP conversation. These commands will help you retrieve and analyze audio data effectively.

Whether you're conducting network analysis, troubleshooting VoIP issues, or simply curious about the inner workings of RTP streams, mastering these tools will enhance your skill set significantly. Happy analyzing!

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