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WHEP client

An input that lets you connect to a WHEP server endpoint to receive video and audio from it.

Usage

To use WHEP Input you must register it first. You can do it by sending a request like this:

Example request 

POST: /api/input/:input_id/register
Content-Type: application/json


{
  "type": "whep_client",
  "endpoint_url": "https://example.com/whep",
  "bearer_token": "<TOKEN>",
  "video": {
    "decoder_preferences": ["ffmpeg_h264", "any"]
  }
}

Reference

Type definitions 

type WhepClient = {
  type: "whep_client";
  endpoint_url: string,
  bearer_token?: string;
  video?: VideoOptions;
  required?: bool;
  buffer_size_ms?: f64;
  side_channel?: SideChannel;
};

Parameters for registering a WHEP client as an input.

Properties

endpoint_url

WHEP endpoint URL from which to receive the media stream.

  • Type: string

bearer_token

Bearer token used for authentication with the WHEP endpoint.

  • Type: string

video

Parameters of a video included in the WHEP stream.

required

Determines if the input stream is essential for output frame production. If set to true and the stream is delayed, Smelter will postpone output frames until the stream is received.

  • Type: bool
  • Default value: false

buffer_size_ms

Minimum and starting size of the jitter buffer in milliseconds. The buffer adapts dynamically based on observed network jitter but will not shrink below this value. Higher values trade latency for resilience.

  • Type: f64

side_channel

Enable side channel publishing for this input. The external consumer reads decoded frames / audio from a Unix socket created under SMELTER_SIDE_CHANNEL_SOCKET_DIR.

VideoOptions

Parameters of a video source included in the WHEP stream.

Type definitions 

type VideoOptions = {
  decoder_preferences?: VideoDecoder[];
};

Properties

decoder_preferences

An ordered list of preferred video decoders. The first element in the list has the highest priority during WHEP negotiation.

Behavior:

  • If the list ends with “any”:

    • Smelter will first try the decoders explicitly listed (in order) and use the first one that is supported and negotiated in WHEP signaling.
    • If none of the listed decoders are supported, Smelter will fall back to any supported codec from the negotiated list that wasn’t already in the preferences.

  • If “any” is not included:

    • Only the decoders listed will be considered.
    • If none are supported, no fallback will occur.

VideoDecoder

Video decoder type.

Type definitions 

type VideoDecoder =
  | "ffmpeg_h264"
  | "ffmpeg_vp8"
  | "ffmpeg_vp9"
  | "vulkan_h264"
  | "any";

  • Type: “ffmpeg_h264” | “ffmpeg_vp8” | “ffmpeg_vp9” | “vulkan_h264” | “any”
  • Supported values:
    • "ffmpeg_h264" - Software H264 decoder based on FFmpeg.
    • "vulkan_h264" (Required feature: gpu-video ) - Hardware decoder. Requires GPU that supports Vulkan Video decoding.
    • "ffmpeg_vp8" - Software VP8 decoder based on FFmpeg.
    • "ffmpeg_vp9" - Software VP9 decoder based on FFmpeg.
    • "any" - Automatically selects any video decoder supported by Smelter.

SideChannel

Per-track side channel configuration. See the Side Channel overview for details on how decoded data is exposed and consumed.

Type definition 

type SideChannel = {
  video?: bool;
  audio?: bool;
  delay_ms?: f64;
};

Properties

video

Publish decoded RGBA video frames for this input on the side channel.

  • Type: bool
  • Default value: false

audio

Publish decoded PCM audio batches for this input on the side channel.

  • Type: bool
  • Default value: false

delay_ms

Side channel delay in milliseconds. Frames are buffered for this duration ahead of when the queue consumes them, so the side-channel subscriber receives them early and has roughly this much time to process before the frame is due.

  • Type: f64
  • Default value: 0