How can I convert the RTP payload containing SILK-encoded audio into a file?

1
votes

I have the pcap of a VoIP call involving SILK. I'm able to see in Wireshark the RTP payload. From the RTP headers I can understand the sample rate (e.g. 24 KHz) and the frame size (e.g. 20 ms). What I'd like to do is extract the RTP payload and generate a file containing the SILK-encoded audio. From the RTP payload format description I can see that in the case of storage in a file, each block of audio needs a block header, to specify the sample rate and block size (because the block size is variable and can be different on each frame).

How can I generate a file with the correct file header ("magic number") and add a block header for each block of audio?

I can use a few different programming languages so I'm mainly interested in the required algorithm, but would appreciate references to code implementations (or perhaps some existing tool?).

1
wiresharkrtpcodec

1 Answers

4
votes

Use pcaputil of pjproject: Converts captured RTP packets in PCAP file to WAV file or play it to audio device. Can filter the PCAP file on source or destination IP or port, is able to deal with SRTP and supports all codecs in PJMEDIA, including SILK (have not tried this myself).

Examples:

pcaputil file.pcap output.wav

pcaputil -c AES_CM_128_HMAC_SHA1_80 -k VLDONbsbGl2Puqy+0PV7w/uGfpSPKFevDpxGsxN3 file.pcap output.wav