Produce RTP stream and dump it directly to a `.pcap` file

[vadimkantorov]

IIUC, currently opusrtp only can broadcast the packets into a TCP socket, right?

Is it possible to save it to disk / broadcast them to a Linux pipe/file stream instead? Or maybe does opus_demo / opusenc / opusrtp already support it? Related to:

• opusrtp: Implement DTX support #46
• opusenc: add 4x opusenc options #64

This is useful for RTP testing purposes / checking the produced bit stream. The idea would be to test how DTX impl + RTP allows to save disk space for audios with a lot of silence.

Thanks :)