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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



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