Function parse_muxed_rtp_fixed_header 

pub fn parse_muxed_rtp_fixed_header(packet: &[u8]) -> Option<RtpFixedHeader>

Parses the fixed RTP header of an RTP candidate in a muxed session.

The parser rejects RTCP candidates, non-RTP versions and packets truncated within the fixed header or declared CSRC list. Codec payload and padding validation belong to the payload parser.

References:

• https://www.rfc-editor.org/rfc/rfc3550.html#section-5.1
• https://www.rfc-editor.org/rfc/rfc5761.html#section-4