The PCAP contained a SIP phone call.
One end is a rickroll, the other end is an AX25 audio capture.
With most common parameters (AFSK 1200bit/s, freq0 1200Hz,freq1 2200Hz).
Decode AX25. (How? Figure it out!)
The stream inside is a TCP connection, whose payload is a PNG image.
Which is a QR code.