GoOSD is a Go/Ebitengine on-screen display for FPV telemetry. It draws a transparent, always-on-top HUD over an external video or map window.

The application does not decode or receive video packets. Video is expected to be displayed by another process, for example gst-launch-1.0. GoOSD listens for MAVLink telemetry over UDP and renders the HUD overlay on top.

Go OSD over a map

Go OSD over FPV video

Typical OpenIPC/WFB-ng setup:

1. Air unit sends video and MAVLink through WFB-ng.
2. Ground station WFB-ng receives the stream and forwards MAVLink to LAN.
3. A video player or GStreamer pipeline displays the video.
4. GoOSD receives MAVLink telemetry and draws the transparent HUD over that video window.

For WFB-ng, check the ground-station MAVLink forwarding settings, usually in /etc/wifibroadcast under gs_mavlink.

Run with simulated data:

go run ./cmd

Run with MAVLink UDP input:

go run ./cmd -mavlink-udp :16000

Run as a click-through overlay:

go run ./cmd -mavlink-udp :16000 -click-through

Example H.265 video receiver pipeline:

gst-launch-1.0 -v udpsrc port=5600 caps='application/x-rtp, media=(string)video, clock-rate=(int)90000, encoding-name=(string)H265' ! rtph265depay ! avdec_h265 ! videoconvert ! autovideosink sync=false

The current HUD draws:

• Center reticle
• Pitch ladder
• Roll scale and roll value
• Heading
• Speed
• Altitude
• GPS fix, satellites, and HDOP
• Battery percentage, voltage, and current
• RC receiver RSSI
• WFB RSSI, link quality, FEC fixed count, RX error count, and link flags
• Flight mode
• Health text: ARMED, DISARMED, LOW BAT, NO TELEMETRY, or FAILSAFE

HUD text uses Ebitengine text/v2 with the embedded Go Mono font. Text is drawn with outline passes to stay readable on both dark and light video backgrounds.

Telemetry is converted into the renderer-facing DTO in internal/hud.State. This keeps MAVLink transport details out of the drawing code.

The state currently includes:

• Attitude: roll, pitch, yaw
• Heading
• Altitude
• Speed
• GPS fix status
• Battery status
• Radio and WFB link status
• Flight mode
• Health flags
• Last update time

GoOSD uses gomavlib with the MAVLink common dialect.

BATTERY_STATUS values are converted as follows:

• battery_remaining: percent
• voltages and voltages_ext: millivolts to volts
• current_battery: centi-amps to amps

Unknown MAVLink sentinel values are ignored rather than displayed as real zeroes.

For RADIO_STATUS, GoOSD follows the WFB-ng OSD convention:

• rssi: WFB RSSI as signed dBm and also a fallback RC RSSI value
• remrssi: WFB link quality percentage
• rxerrors: WFB link error counter
• fixed: WFB FEC fixed counter
• remnoise: WFB flags

Supported WFB flags:

• 1: link lost
• 2: link jammed

RC_CHANNELS_RAW.rssi and RC_CHANNELS.rssi update the RC receiver RSSI display directly. A value of 255 is treated as invalid or unknown.

Flight mode is derived from HEARTBEAT.base_mode and HEARTBEAT.custom_mode.

For Betaflight-compatible heartbeats, GoOSD follows the current telemetry convention:

• custom_mode = 1: ACRO
• custom_mode = 0: STAB

For other MAVLink senders, GoOSD falls back to the standard mode flags in priority order:

1. AUTO
2. GUIDED
3. STAB
4. MANUAL
5. HIL
6. TEST
7. CUSTOM <custom_mode>

Run tests:

go test ./...

• Add config for window size, position, always-on-top, click-through, and data source.
• Add a background launcher for the video pipeline and GoOSD.

HUD work is based on ideas from Stratux AHRS:

https://github.com/knicholson32/stratux_ahrs/blob/master/LICENSE