User:Joger/Building Qt Multimedia with FFmpeg

My build setup

OS: Windows 11 with dev drive mounted on D: (Using a dev drive makes builds faster when using Windows Defender antivirus)

Qt source tree: D:\qt\qt6\

Build directory containing all builds: D:\qt\build\

Main (host) build for dev branch: D:\qt\build\dev\

Visual Studio 2022 (MSVC)

Don't have perl in path as it can cause hard to understand build failures

Have cmake in path

Developer setup for Qt Multimedia

Initializing Qt Repo for Qt 6 with necessary dependencies for QtMultimedia

This init-repository initializes the necessary Qt submodules for working with QtMultimedia. By only initializing the repository with the necessary modules, the main Qt build is faster than doing a full build.

C:\Strawberry\perl\bin\perl init-repository --module-subset=qtbase,qtquick3d,qtdeclarative,qtsvg,qtshadertools,qtmultimedia,qtrepotools -f --codereview-username johanseg

Building FFmpeg on Windows

1. Install 7-zip from provisioning: Run qt6\coin\provisioning\common\windows\install-sevenzip.ps1 as admin
   • Needed by provisioning script for FFmpeg to unzip downloaded FFmpeg
2. Install msys2 from provisioning: Run qt6\coin\provisioning\common\windows\install-msys2.ps1 as admin
   • Needed by provisioning script for FFmpeg because FFmpeg requires tools from msys to configure
3. Install FFmpeg from provisioning: Run qt6\coin\provisioning\common\windows\install-ffmpeg.ps1 as admin
   • Since I only need MSVC build, I edit the install-ffmpeg.ps1 first, to comment out unnecessary versions
   • This sets FFMPEG_DIR=C:\FFmpeg-n6.0\build\msvc\installed\

Configure Qt main build

I build Qt as stand-alone module to make builds run faster when working in QtMultimedia. But first, we need to build the necessary dependencies. I do this from command line with D:\qt\build\dev as current directory.

..\..\qt6\configure.bat -debug -developer-build -submodules QtMultimedia -nomake tests -nomake examples -- -DFFMPEG_DIR=C:\FFmpeg-n6.0\build\msvc\installed --fresh & ninja

I work almost exclusively using debug builds. If you need a release build, configure the release build in a separate build directory. This is a developer build, and we can use D:\qt\build\dev\qtbase\ as CMAKE_PREFIX_PATH when developing other Qt modules. By configuring this way, QtMultimedia is built, which is not strictly necessary since I develop QtMultimedia in a separate build tree, but it is an easy way to make sure all QtMultimedia dependencies are built.

Configure Qt multimedia

I configure QtMultimedia using a CMakeUserPresets.json file that is located in D:\qt\qt6\qtmultimedia instead of using a configure script. This way, I can open the D:\qt\qt6\qtmultimedia as a folder in Visual Studio and configure it from there.

The benefit of using CMakeUserPresets.json is that Visual Studio knows how to debug the tests and examples. I have not found a way that allows Visual Studio to use an existing CMakeCache as a starting point.

{
    "version": 5,
    "configurePresets": [
        {
            "name": "msvc-64",
            "hidden": true,
            "condition": {
                "type": "equals",
                "lhs": "${hostSystemName}",
                "rhs": "Windows"
            },
            "generator": "Ninja",
            "cacheVariables": {
                "CMAKE_CXX_COMPILER": "cl.exe",
                "CMAKE_C_COMPILER": "cl.exe"
            },
            "toolset": {
                "value": "v143,host=x64",
                "strategy": "external"
            },
            "architecture": {
                "value": "x64",
                "strategy": "external"
            }
        },
        {
            "name": "Debug",
            "hidden": true,
            "cacheVariables": {
                "CMAKE_BUILD_TYPE": "Debug"
            }
        },
        {
            "name": "qt6-dev-base",
            "hidden": true,
            "cacheVariables": {
                "FEATURE_developer_build": true,
                "BUILD_qttools": false,
                "BUILD_qtdoc": false,
                "BUILD_qttranslations": false,
                "QT_BUILD_EXAMPLES": false,
                "QT_BUILD_EXAMPLES_BY_DEFAULT": false,
                "QT_BUILD_EXAMPLES_AS_EXTERNAL": false,
                "QT_BUILD_TESTS": false,
                "QT_BUILD_TESTS_BY_DEFAULT": false
            },
            "environment": {
                "PATH": "D:/qt/build/dev/qtbase/bin;$penv{PATH}"
            }
        },
        {
            "name": "qt6-dev-debug",
            "hidden": true,
            "inherits": [
                "qt6-dev-base",
                "msvc-64",
                "Debug"
            ],
            "cacheVariables": {
                "CMAKE_PREFIX_PATH": "D:/qt/build/dev/qtbase/"
            },
            "environment": {
                "PATH": "D:/qt/build/dev/qtbase/bin;$penv{PATH}"
            }
        },
        {
            "name": "QtMultimedia",
            "inherits": "qt6-dev-debug",
            "binaryDir": "D:/qt/build/qtmultimedia/",
            "cacheVariables": {
                "QT_BUILD_EXAMPLES": true,
                "QT_BUILD_EXAMPLES_BY_DEFAULT": true,
                "QT_BUILD_TESTS": true,
                "QT_BUILD_TESTS_BY_DEFAULT": true,
                "QT_BUILD_EXAMPLES_AS_EXTERNAL": false,
                "QT_BUILD_MANUAL_TESTS": false,
                "QT_DEPLOY_FFMPEG": true,
                "FEATURE_ffmpeg": true,
                "FFMPEG_DIR": "C:\\ffmpeg-n6.0\\build\\msvc\\installed"
            }
        }
    ],
    "buildPresets": [
        {
            "name": "Build-Qt-Multimedia-MSVC-Debug-64",
            "displayName": "Build Qt Multimedia MSVC Debug 64",
            "configurePreset": "QtMultimedia"
        }
    ]
}