cv710userspace

An independent, reverse-engineered userspace capture driver for the AVerMedia ExtremeCap U3 (CV710, USB 07ca:0710) on Linux.

Not affiliated with AVerMedia. This is an independent interoperability project. It is not affiliated with, authorised by or endorsed by AVerMedia. "AVerMedia", "ExtremeCap U3" and "CV710" are trademarks of their respective owners, used only to identify the hardware. See Legal.

It displays captured video and audio in a standalone SDL3 window, or forwards the stream to a virtual V4L2 loopback device for OBS, Discord or a browser. There is also a Windows build, described in WINDOWS.md.

• Status: experimental, forked from ChrisAJS/lgx2userspace, provided without warranty. It reimplements the official driver's behaviour from observation; no vendor source is used.
• Related project: the kernel-space sibling is avmcv710, which exposes the same hardware as a standard capture node instead of a userspace app. The two are alternatives, so you need one or the other, not both. See Setup for running them side by side.
• Docs: PROTOCOL.md and ISSUES.md.

Contents

• Component video input
• Requirements
• Building
• Setup
• Running
• V4L2 output
• Audio routing
• Hardware frame-rate converter
• Legal
• Attributions

Component video input

Not supported. Capture on the ExtremeCap U3 is HDMI only. The component input needs a proprietary multi-pin breakout cable plus ADV7604 analog front-end calibration, sync-slicer clock locking and analog audio routing through the onboard TLV320AIC3101 codec. Switching inputs in software without those routines only corrupts the HDMI contrast and brightness levels.

Requirements

• CMake 3.18+
• libusb 1.0
• SDL3
• V4L2Loopback (optional, for the virtual webcam output)

Building

# Ubuntu / Debian (24.04+)
sudo apt install cmake g++ libusb-1.0-0-dev libsdl3-dev v4l2loopback-dkms v4l2loopback-utils

# Arch Linux
sudo pacman -S cmake gcc libusb sdl3 v4l2loopback-dkms v4l2loopback-utils

# Fedora
sudo dnf install cmake gcc-c++ libusb1-devel SDL3-devel v4l2loopback

cmake -S . -B build -DCMAKE_BUILD_TYPE=Release
cmake --build build -j$(nproc)

Setup

The driver needs read and write access to the CV710 USB device. Install the udev rules and re-plug the device:

sudo cp 99-avermedia-cv710.rules /etc/udev/rules.d/
sudo udevadm control --reload-rules
sudo udevadm trigger

Coexisting with the avmcv710 kernel driver. This driver needs exclusive access to the USB interface. If the kernel V4L2 driver is bound, libusb detaches it on claim and re-attaches it on exit, so both can be installed side by side, as long as nothing is streaming through the kernel driver. If an application such as OBS is using avmcv710 at the same time, the claim fails. Close it, or unload the module first with sudo modprobe -r avmcv710.

Running

./build/src/cli/cv710userspace

The application initialises the hardware and streams 1080p60 uncompressed video and audio to the SDL3 preview window. The console is quiet by default: it prints event-driven lines only (resolution changes, lock status, drops, errors). Add -v or -V for the throttled per-transfer and per-frame chatter.

Keys:

• Tab / O: toggle the diagnostic HUD (input, colour, audio, capture status).
• C: cycle colour profiles (BT.709 limited, BT.709 full range, BT.601, UYVY, raw YUY2).
• F / G: enter / leave fullscreen.
• R: re-anchor the parser on the next frame marker. This is a software re-sync only, with no hardware writes (mid-stream FPGA/FX3 resets were field-tested and corrupt the stream). Use it if the picture gets skewed or misaligned and stays that way. The parser also re-anchors automatically after about 1 second of continuously corrupt frames, capped at 2 attempts; if it is still stuck, replug the device.
• Esc: quit.

Resolution and colour changes show a small bottom-centre toast; the full HUD appears only on Tab / O.

The OSD uses an antialiased TTF (Inter, Noto Sans or Fira Sans are auto-detected). Force a specific font with CV710_FONT=/path/to/font.ttf, or drop one at assets/fonts/ui.ttf. Without a TTF it falls back to the built-in SDL debug font.

Flags:

• -d DEVICE: forward the stream to a V4L2 loopback device (see V4L2 output).
• -c COLOR: initial colours profile (bt709, bt709full, bt601, bt601full, uyvy, yuy2).
• -S SCALE: output scaling (1 full, 2 half, 4 quarter).
• --aspect MODE: preview aspect handling. stretch (default) fills the window, auto preserves each source's natural DAR (480p/576p as 4:3, HD as 16:9), 4:3 and 16:9 force that DAR. Non-stretch modes pillarbox or letterbox in black instead of squashing.
• -g: video only. -s: audio only (no video preview).
• -v: exit summary. -V: real-time timing. Both enable the throttled console chatter.
• --audio-device NAME|INDEX, --audio-loopback, --list-audio-devices: see Audio routing.
• --convert MODE, --list-cvx8897: see Hardware frame-rate converter.

V4L2 output

Load v4l2loopback and run with -d:

sudo modprobe v4l2loopback video_nr=99 exclusive_caps=1 card_label="CV710"
ls -l /dev/video99
./build/src/cli/cv710userspace -d /dev/video99

Then add a Video Capture Device (V4L2) in OBS and select CV710 (/dev/video99).

Audio routing

V4L2 carries video only, so the captured 48 kHz stereo audio is played through SDL's default playback device. There are three ways to keep it off your desktop speakers:

1. -g: disable audio entirely. Nothing plays, and there is no audio to record either.
2. --audio-loopback: route audio into a virtual sink so OBS or Discord can record it as a separate source. It makes the loopback a hard requirement: if none is found, the driver errors out instead of falling back to the speakers.

   sudo modprobe snd-aloop          # option A: ALSA loopback
   pw-loopback --name CV710_Audio   # option B: PipeWire null sink
   ./build/src/cli/cv710userspace -d /dev/video99 --audio-loopback

3. --audio-device NAME|INDEX: point at an explicit device, for example a null sink or a specific capture endpoint.

   ./build/src/cli/cv710userspace -d /dev/video99 --audio-device "Loopback"

With -d and no explicit device, a loopback sink is preferred; if none is present the driver falls back to the desktop default (with a hint in the log) rather than dropping the audio. --audio-loopback upgrades that to a hard requirement. --list-audio-devices shows what SDL can see, with loopback devices marked <-- loopback (capturable).

To record it, point your app at the capture side of the sink, not the monitor you would listen through:

• snd-aloop: an ALSA audio input at Loopback: Loopback PCM.
• PipeWire (pw-loopback / CV710_Audio): the device's Monitor input, or use pavucontrol to route the sink's monitor stream.

Video and audio then arrive as two independent sources: video from /dev/video99, audio from the loopback monitor.

Hardware frame-rate converter (CVX8897)

--convert MODE drives the CVX8897, the chip between the HDMI receiver and the capture path. native (the default) leaves it untouched; half and auto halve the delivered rate for the detected input (1080p60 to 30p, 1080p50 to 25p, 720p60 to 30p, and so on); any mode name from --list-cvx8897 forces a specific table. Geometry is unchanged, so the parser still classifies correctly. Bench-verified: a 1080p60 source captures at about 30 fps while the HUD's INPUT row still reports 60 Hz.

A few things are worth knowing:

• The converter latches its mode across app runs; only a reset or a power cycle clears it. If you ran --convert half and then launch without --convert, you still get about 30 fps. Run --convert reset (or power-cycle) to return to native 60 fps passthrough.
• The converter is re-programmed whenever the detected input changes, not just at startup. Modes with no table (SD, interlaced, 24p/30p and unregistered geometry) fall back to native passthrough instead of leaving the previous table latched. A live re-program replays a roughly 3 second reset pulse, so each convertible-mode switch shows a brief re-lock.
• The vendor sequence (SetMode() / HWReset(), a reset pulse through the PCA9539 GPIO expander, plus the output enable) runs before the 251-register table, because the table alone leaves the converter's output PLL dead. The first apply completes before streaming starts.
• --convert reset is the recovery mode: it replays the HWReset preamble and restores native output without waiting for a lock. Use it if an experiment left the converter in a bad image and the source will not lock (a physical power cycle is the guaranteed fallback).

Protocol documentation

The USB bulk streaming protocol, framing markers, FPGA checksum validation and audio format are documented in PROTOCOL.md. Known hardware limitations are tracked in ISSUES.md.

Legal

Not legal advice. If any of this matters to you, talk to a lawyer.

• No affiliation. Independent interoperability project, not affiliated with, authorised by or endorsed by AVerMedia. "AVerMedia", "ExtremeCap U3" and "CV710" are trademarks of their respective owners, used only to identify the hardware this project targets.
• Reverse-engineered for interoperability. Written by observing the device's own USB traffic and the vendor's shipped binaries. It contains no vendor source code.
• No HDCP, no circumvention. The project implements no HDCP: no authentication, no key material, no cipher, no key derivation. The bootstrap sequence initialises the receiver for raw digitisation only. Whatever a protected source does here, it does because of the hardware, not because of this code. See ISSUES.md section 6.
• Your responsibility. Whether you may capture, record or redistribute any particular signal is governed by laws such as the DMCA (17 U.S.C. 1201) and the EU Information Society Directive (Art. 6) and by the terms of the content's licence. That is between you and the rights holders.
• Vendor assets. The standby overlay bitmaps in assets/ are AVerMedia's artwork, reproduced so the presentation matches the official driver. Copyright remains with AVerMedia; remove them if that is a problem for your distribution.
• No warranty. Provided "as is", without warranty of any kind. See LICENSE.md.

Attributions

Forked from lgx2userspace by Chris Sawczuk (ChrisAJS), and built on:

• libusb
• SDL3
• V4L2Loopback
• Catch2
• AVerMedia for the ExtremeCap U3 hardware and the standby overlay artwork in assets/ (see Legal)