Module rtx 

RFC 4588 RTX (Retransmission) helpers.

Packet format: RTX payload = 2-byte Original Sequence Number (OSN, network order) followed by the original RTP payload. RTX uses a dedicated SSRC and payload type associated with the primary codec via a=fmtp:<rtx-pt> apt=<primary-pt>.

Structs

RtxSenderConfig

Sender-side RTX parameters negotiated for a primary media stream.

Functions

allocate_rtx_payload_type

Pick a free dynamic payload type (96–127) not in used.

append_rtx_to_section

Append RTX rtpmap/fmtp lines and the PT to formats for a primary codec.

decode_osn

Decode OSN from the first two bytes of an RTX payload.

encode_osn

Encode OSN as big-endian bytes (test / debug helper).

extract_rtx_apt_map

Build RTX PT → primary PT map from media-section attributes.

extract_rtx_apt_map_from_attrs

Convenience over SDP Attribute list.

parse_apt

Parse apt=<pt> from an SDP fmtp value (e.g. "apt=96" or "apt=96;rtx-time=3000").

rtx_pt_for_primary

Find RTX payload type associated with primary_pt in an apt map.

unwrap_rtx_packet

Unwrap an RTX packet back into a primary media packet.

wrap_rtx_packet

Wrap a primary media packet into an RFC 4588 RTX retransmission packet.

Type Aliases

RtxAptMap

Association parsed from SDP: RTX payload type → primary (associated) payload type.