# `XMediaLib.SDP.RtcpFb`
[🔗](https://github.com/Lazarus404/xmedialib/blob/main/lib/sdp/types.ex#L363)

RTP/AVPF feedback (`a=rtcp-fb:`) declaring RTCP feedback capabilities.

## What problem this solves

WebRTC declares RTCP feedback capabilities (NACK, PLI, transport-cc) in
`a=rtcp-fb:` attributes so endpoints know which AVPF messages are allowed.
This struct represents one declared feedback token for a payload type.

Used for NACK, PLI, FIR, and transport-wide congestion control tokens.

Wire form: `a=rtcp-fb:<pt> <type> [<param>]`

## RFCs

* [RFC 4585](https://www.rfc-editor.org/rfc/rfc4585) - AVPF
* [RFC 5104](https://www.rfc-editor.org/rfc/rfc5104) - codec control messages

# `t`

```elixir
@type t() :: %XMediaLib.SDP.RtcpFb{
  parameters: String.t() | nil,
  payload_type: String.t(),
  type: String.t()
}
```

Payload type (or `*`), feedback type, and optional parameters.

## Fields

* `:payload_type` - RTP payload type or `*` for all formats
* `:type` - feedback token, e.g. `nack` or `transport-cc`
* `:parameters` - optional subtype or parameter string

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*Consult [api-reference.md](api-reference.md) for complete listing*