openipc-core

Shared protocol code for openipc-rs.

This crate contains the parts of the OpenIPC receive path that do not need to know whether bytes came from native USB, WebUSB, a capture file, or a test fixture. It is the right dependency when you want to parse or reconstruct OpenIPC video without taking a dependency on a specific USB frontend.

What It Does

Parse Realtek rtl88xx USB RX aggregates and 24-byte RX descriptors.
Filter OpenIPC/WFB 802.11 frames by channel id and radio port.
Handle WFB session packets, optional session TLVs, data decryption, and FEC recovery.
Expose recovered non-video WFB payload bytes from telemetry, tunnel/data, audio, or custom radio ports without parsing those application protocols.
Parse RTP and depacketize H.264/H.265 into Annex-B access units.
Expose RTP payload bytes for app-owned sinks such as UDP forwarding or Opus audio decoding.
Build adaptive-link feedback payloads and WFB uplink packets.
Build radiotap + 802.11 WFB transmit frames. Hardware crates add their own USB/driver descriptors before transmission.

Basic Receive Shape

use openipc_core::{
    ChannelId, FrameLayout, PayloadRouteId, ReceiverBatchOptions, ReceiverRuntime,
    WfbKeypair,
};

const VIDEO_ROUTE: PayloadRouteId = PayloadRouteId::new(1);

fn push_transfer(
    receiver: &mut ReceiverRuntime,
    transfer: &[u8],
) -> Result<Vec<Vec<u8>>, Box<dyn std::error::Error>> {
    let batch = receiver.push_rx_transfer(transfer, &ReceiverBatchOptions::default())?;
    Ok(batch.frames.into_iter().map(|frame| frame.data).collect())
}

fn receiver_from_keypair(keypair_bytes: &[u8]) -> Result<ReceiverRuntime, Box<dyn std::error::Error>> {
    let keypair = WfbKeypair::from_bytes(keypair_bytes)?;
    Ok(ReceiverRuntime::with_keyed_video_route(
        FrameLayout::WithFcs,
        VIDEO_ROUTE,
        ChannelId::default_video(),
        0,
        keypair,
        0,
    )?)
}

The returned frame data is still encoded video. Feed it to WebCodecs, a native decoder, a file writer, or an RTP/Annex-B bridge depending on your application. Long-running receivers should treat per-frame WFB errors as dropped packets and continue scanning the current USB aggregate.

Payload Routes And RTP

PayloadPipeline is the lower-level channel-recovery state machine in openipc-core. It emits recovered bytes after channel filtering, WFB session handling, decryption, and FEC. It does not parse RTP, MAVLink, MSP, CRSF, IP, vendor data, or any other application protocol.

Most apps should start with ReceiverRuntime. It wraps PayloadRouteManager and the RTP depacketizer used for the configured video route. The route manager keeps one runtime per (channel_id, key_slot) and attaches one or more route IDs to that runtime. This avoids decrypting and FEC-recovering the same channel twice when you want multiple outputs, such as local video display plus RTP forwarding.

For OpenIPC video, configure one video route. Recovered payloads on that route are treated as RTP and are turned into Annex-B H.264/H.265 frames. If you also want RTP forwarding, ask ReceiverRuntime to tap the same route as raw payload bytes:

use openipc_core::{PayloadRouteId, ReceiverBatchOptions, ReceiverRuntime};

const VIDEO_ROUTE: PayloadRouteId = PayloadRouteId::new(1);

fn receive_with_rtp_tap(
    receiver: &mut ReceiverRuntime,
    transfer: &[u8],
) -> Result<(), Box<dyn std::error::Error>> {
    let batch = receiver.push_rx_transfer(
        transfer,
        &ReceiverBatchOptions {
            raw_payload_routes: vec![VIDEO_ROUTE],
            ..ReceiverBatchOptions::default()
        },
    )?;

    for rtp in batch.raw_payloads {
        println!("RTP bytes: {}", rtp.data.len());
    }
    for frame in batch.frames {
        println!("Annex-B frame bytes: {}", frame.data.len());
    }
    Ok(())
}

Add another route for a non-video WFB channel when you want recovered telemetry, IP/VPN, or custom bytes:

use openipc_core::{
    ChannelId, PayloadRouteId, RadioPort, ReceiverBatchOptions, ReceiverRuntime,
    WfbKeypair,
};

const TELEMETRY_ROUTE: PayloadRouteId = PayloadRouteId::new(2);

fn add_telemetry_route(
    receiver: &mut ReceiverRuntime,
    keypair_bytes: &[u8],
    port: RadioPort,
) -> Result<(), Box<dyn std::error::Error>> {
    let keypair = WfbKeypair::from_bytes(keypair_bytes)?;
    receiver.add_keyed_route(
        TELEMETRY_ROUTE,
        ChannelId::from_link_port(7669206, port),
        0,
        keypair,
        0,
    )?;
    Ok(())
}

fn handle_transfer(
    receiver: &mut ReceiverRuntime,
    transfer: &[u8],
) -> Result<(), Box<dyn std::error::Error>> {
    let batch = receiver.push_rx_transfer(
        transfer,
        &ReceiverBatchOptions {
            raw_payload_routes: vec![TELEMETRY_ROUTE],
            ..ReceiverBatchOptions::default()
        },
    )?;
    for payload in batch.raw_payloads {
        println!(
            "route={} channel=0x{:08x} bytes={}",
            payload.route_id.raw(),
            payload.channel_id.raw(),
            payload.data.len()
        );
    }
    Ok(())
}

RadioPort::TelemetryRx is OpenIPC's observed telemetry downlink port. That stream may contain MAVLink, MSP/OSD, or another router-specific payload. Use RadioPort::TunnelRx, RadioPort::AudioRx, or RadioPort::Custom(n) for other payload channels. openipc-core does not parse MAVLink or any other telemetry protocol. Applications can parse, display, record, or inspect those bytes later.

Audio follows the same rule, with one extra helper. OpenIPC-documented audio is usually Opus RTP payload type 98 mixed into the main video RTP route. Use ReceiverBatchOptions::rtp_payload_taps to copy only that payload type while the video depacketizer keeps consuming the same route. Custom wfb-ng profiles can also carry audio on a separate route such as RadioPort::AudioRx. openipc-core still does not own audio playback; it only provides recovered RTP packet bytes and metadata.

RtpDepacketizer is also conservative about fragmented video. If a fragmented H.264/H.265 RTP access unit has a sequence gap, the partial frame is dropped and the depacketizer waits for the next clean fragment start.

Crate Boundaries

openipc-core intentionally has no USB device ownership. Pair it with:

openipc-rtl88xx for native or WebUSB Realtek adapter IO.
openipc-web or @openipc-rs/web for browser/WASM applications.
apps/openipc-cli for CLI-style native receive-loop examples.

Status

The protocol pipeline has unit tests for parser, crypto, FEC, RTP, and uplink helpers. Live radio behavior still depends on the USB driver and adapter validation in higher-level crates.

An optional PixelPilot/wfb-ng reference test can compare Rust FEC output against PixelPilot's vendored zfex.c implementation:

OPENIPC_PIXELPILOT_REF=/path/to/PixelPilot \
  cargo test -p openipc-core --test pixelpilot_reference -- --ignored --nocapture