Audio and Video Calls.

Call request (ring)
[0x70 0x70]
[2 pseudo-random octets]

Call answer (pick up)
[0x71 0x71]
[2 pseudo-random octets]

Call reject 
[0x72 0x72]
[2 pseudo-random octets]

Call hang up (finished)
[0x73 0x73]
[2 pseudo-random octets]

Audio stream parameters
[0x74 0x74]
[codec - 20 octet string, left-aligned, padded with zeroes,
"opus", "adpcm_g722", "pcm_alaw" named as in ffmpeg]
[sample rate, uint16_t little-endian]

Video stream parameters
[0x75 0x75]
[codec - 20 octet string, left-aligned, padded with zeroes, e.g.
"hevc", "h264", "mjpeg", "vp9", named as in ffmpeg]
[width, uint16_t, little-endian]
[height, uint16_t, little-endian]

Voice (audio) packet
[0x76 0x76][length 2 octets][data]

Video packet
[0x77 0x77][length 2 octets][data]