---

Overview

V4l2Camera is an attempt to abstract the video4linux2 api into something more easily usable in a generic C++ application

• I set out, naively, to create cross-platorm support (Linux, MacOS, Windows) but soon realized the extent of that effort
• The linux version is "done", although I know there are lots of refinements possible/needed/required
• I think I see a path forward on the MacOS and Windows side of things after starting down a few interesting pathways (libuvc, libusb)

Details

• Low level camera control using (or emulating) the video4linux2 interface

• Currently supporting Linux based systems (tested on Debian AMD64 and Raspbian ARM64 platforms)

  • support planned for MacOS (via AVFoundation api), and
  • Windows (via Media.Capture api)

• Designed to support both command line and GUI based applications

• Example code provided for command line application, sample application (binary-only) provided for GUI based application

• Distributed as open-source under the MIT License

---

Index

• -here- V4l2Camera Overview
• -here- API/Class Details
• -here- Command Line Example Code
• -here- camControl Cross Platform GUI app
• -here- Image Conversion Functions

---

Distribution

• The v4l2camera class source code is distributed as open source under the MIT License
  • If you use it and find it useful, drop me a line and let me know
  • Provide attribution and a link back to the github repo so more people can find the code and use it (please)
  • I have gained so much information from the open source community that I figured it was time to give back
• The camControl app is distributed free of charge on Linux platforms, all rights for this app remain with the developer
  • will decide how to distribute the MacOS and Windows versions once they exist

---

Build Dependencies

General

• Makefile is absolutely generic, I spent time on the source code and know I could clean up the Makeifle, will get to it :)
  • Currenly uses the gcc/g++ compiler and has been tested on Linux and MacOS (sort of)
  • MacOS version has not attempted to include AVFoundation api so may require changes to use the LLVM compiler and different include paths
  • Windows version has not been started
• Makefile will be updated to use native compiler on each platform (as required, would prefer to use gcc/g+ if possible)

Linux

• Dependent only on the std C++ library

MacOS

• In progress, will (hopefully) be designed to work with the AVFoundation api

Windows

• In progress, will be designed to work with the Media.Capture api

---

Building V4l2Camera into your own App

Download

• Download or clone the git repo (this repo)

$ git clone https://github.com/danlargo/v4l2Camera.git

Make (MAC and Linux)

• Run make in the source folder, this will create the example binary (v4l2cam) and create a distribution folder for inclusion in other apps (v4l2cam-dist)

$ cd v4l2camera
$ make

• Copy the distribution folder into the top level of your project

$ cp -r ./v4l2cam-dist ../myProject

Make (Windows)

• Check out this link for help if command line tools are not installed - here

• Verify the C++ command line tools are installed

  • Open a Developer Power Shell from the Visual Studio app
    • Tools -> Command Line -> Developer Power Shell
  • change folder to v4l2camera
  • run nmake

C:\...> cd v4l2camera
C:\...> dir
...should show the file structure for v4l2camera

c:\...> nmake

• should build the v4l2camera library and command line files

  • might say "nmake : The term 'nmake' is not recognized as the name of a cmdlet...", which means the command line tools are not installed or not in the command path

• Copy the distribution folder into the top level of your project

$ cp -r ./v4l2cam-dist ../myProject

Add to your project source - Linux

#include "../linux/linuxcamera.h"
.
.
.
// generate a list of UVC cameras available in the system

std::vector<LinuxCamera*> camlist = LinuxCamera::DiscoverCameras();

if( camlist.size() == 0 ) std::cerr << "No Cameras in System??" << std::endl;
else
{
    LinuxCamera * cam = camList[0];
    if( !cam->open() ) std::cerr << "Camera is not accessible - Not Open" << std::endl;
    else
    {
        // do stuff here

    }
}

Add to your Makefile

g++ -g -std=c++20 -o main.o main.c
g++ -g -o main main.o v4l2cam-dist/libv4l2cam-linux-arm64.a

---

Example Code

• See command line example folder

---

Sample App - camControl

• camControl is built to run in Linux AMD64 and ARM64 GUI environments
  • built on Debian Linux (AMD64), and
  • Raspbian, ARM64
• It is distributed on Linux platforms free of charge.

---

Class method documentation

• Here

---

Image Conversion Functions

• Information I have collected around the internet regarding conversion from YUV imager formats to generic RGB32 bitmaps
• Here

---

ToDo

• Add better support for fourCC codes in Video modes

  • currently lookup and display is managed via string version of fourCC code, which is not guarranteed to be unique
  • fourCC convertion functions are provided in v4l2camera.cpp but not used in video mode queries and selection

• Add User Control interface into example command line app (v4l2cam)

  • User Controls are fully supported in the V4l2Camera class

• MacOS support for V4l2Camera

  • went down a few blind alleys...
    • libucv here
      • not unhappy with the api, but found it frustrating in that they still haven't dealt with the app permission issue on MacOS (which may not be solveable)
    • libusb here
      • for obvious reasons it felt like I was simply duplicating the libuvc effort
    • QCamera (on Qt 6) here
      • this effort proved the most frustrsating as I am using Qt as a cross platform GUI development environment (maybe that is my issue)
      • Qt 6 is not supported on Raspbian, which is where the majority of my development is these days, Qt 5 does not support QCamera
      • QCamera is able to fetch images from USB cameras on MacOS but has zero support for any User Controls
        • I have a question ticket here into Qt Forum but have received no response
        • This seems to be an issue that has existed for a while.
  • Everything I am reading is pointing towards having to deal with the AVFoundation api from Apple.
    • All documentation points to XCode and Swift/Objective-C
    • I want to provide command line and GUI support for C++, so may be banging my head on a wall here
    • I want to make sure to properly support the request and maintenance of proper user/device permissionsas well

• MacOS build of camControl

  • will use this an indication that the class library actually works on MacOS

• Windows support

  • looking at the Media.Capture api
  • very preliminary

• Windows build of camControl

  • will use this an indication that the class library actually works on Windows