RTP header information
V 2-bits, version number (=2)
P 1-bit, indicates padding
X 1-bit, indicates extension header present
CC 4-bits, number of CSRCs (CSRC count)
M 1-bit, profile specific marker (defined elsewhere)
PT 7-bits, payload type, profile specific (defined elsewhere)
SSRC synchronisation source
timestamp has profile/flow-specific units