CMake: a QML module that uses QtMultimedia (or other Qt non-core module)

paulmasri

I've created a C++ class that uses QtMultimedia classes. If I put this in a QML module, I get a link error for all calls to QtMultimedia classes. What's the solution?

Here's my CMake (which would work if my C++ class wasn't using QtMultimedia):

set(CMAKE_AUTOMOC ON)
set(CMAKE_CXX_STANDARD_REQUIRED ON)

find_package(Qt6 6.2 COMPONENTS Quick Multimedia REQUIRED)

qt_add_executable(appSynth
    main.cpp
)

qt_add_qml_module(appSynth URI SynthesizerApp VERSION 1.0
    QML_FILES main.qml
)

qt_add_qml_module(Synth URI Synth VERSION 1.0
    SOURCES Synthesizer.h Synthesizer.cpp
)
target_include_directories(Synthplugin PUBLIC ${CMAKE_CURRENT_SOURCE_DIR})

target_compile_definitions(appSynth
    PRIVATE $<$<OR:$<CONFIG:Debug>,$<CONFIG:RelWithDebInfo>>:QT_QML_DEBUG>)

target_link_libraries(appSynth PRIVATE Qt6::Quick Qt6::Multimedia Synth)

NB: I tried adding the following, which did result in QtMultimedia metatypes showing up in the Synth "Other Locations" folder, but didn't help the linker:

target_link_libraries(Synth PRIVATE Qt6::Multimedia)

SGaist

Hi,

Which error are you getting ?

paulmasri

I get a whole slew of them regarding calls to functions within QtMultimedia.
e.g.

Undefined symbols for architecture arm64:
  "QAudioSink::start()", referenced from:
      Synthesizer::start() in Synthesizer.cpp.o

SGaist

Building on an M1 Mac machine ?

paulmasri

Yes. MacBook Pro, M1, macOS 12.1, clang 13.0.0.

SGaist

How did you install Qt ?

Because from the looks of it you might be mixing x86_64 and arm64 libraries.

paulmasri

I use Qt's 'Maintenance Tool' installer.

Just in case there had been a problem, I've just uninstalled and reinstalled Qt 6.2.3 with Qt Multimedia. And I deleted the build folder before rebuilding. But I still get this problem.

Any idea how to get around it?

kkoehne

Can you post the full compile output somewhere?

SGaist

Are you building from the command line ?

If so, you should activate an x86_64 shell and only then do your build.

paulmasri

I'm using QtCreator to build.

Above is a minimal version of my actual project. I'm going to create a genuinely minimal project and try building on Mac (M1) and Windows and then I'll reply again.

paulmasri

Sorry, been away on holiday. But I have now created a minimal project and tested it on Mac (M1) and Windows 10, both using Qt Creator 7.0.0 with Qt 6.2.3. I get equivalent errors.

In case it's of relevance, within my code I have to put #include <QtMultimedia/QAudioSink> rather than #include <QAudioSink>. Perhaps it's not just the object linking that's missing, but the include directories too??

Below are:

CMake output on Mac M1
Build output on Mac M1
CMake output on Windows 10
Build output on Windows 10
CMakeList.txt
Synthesizer.h
Synthesizer.cpp
main.cpp
main.qml

CMake output on Mac M1

Running /Users/me/Qt/Tools/CMake/CMake.app/Contents/bin/cmake -S /Users/me/Code/minimalSynthesizer -B /Users/me/Code/build-minimalSynthesizer-Qt_6_2_3_for_macOS-Debug '-DCMAKE_GENERATOR:STRING=Unix Makefiles' -DCMAKE_BUILD_TYPE:STRING=Debug '-DCMAKE_PROJECT_INCLUDE_BEFORE:FILEPATH=/Users/me/Qt/Qt Creator.app/Contents/Resources/package-manager/auto-setup.cmake' -DQT_QMAKE_EXECUTABLE:STRING=/Users/me/Qt/6.2.3/macos/bin/qmake -DCMAKE_PREFIX_PATH:STRING=/Users/me/Qt/6.2.3/macos -DCMAKE_C_COMPILER:STRING=/usr/bin/gcc -DCMAKE_CXX_COMPILER:STRING=/usr/bin/clang++ in /Users/me/Code/build-minimalSynthesizer-Qt_6_2_3_for_macOS-Debug.
-- The CXX compiler identification is AppleClang 13.0.0.13000029
-- Detecting CXX compiler ABI info
-- Detecting CXX compiler ABI info - done
-- Check for working CXX compiler: /usr/bin/clang++ - skipped
-- Detecting CXX compile features
-- Detecting CXX compile features - done
-- Looking for C++ include pthread.h
-- Looking for C++ include pthread.h - found
-- Performing Test CMAKE_HAVE_LIBC_PTHREAD
-- Performing Test CMAKE_HAVE_LIBC_PTHREAD - Success
-- Found Threads: TRUE  
-- Performing Test HAVE_STDATOMIC
-- Performing Test HAVE_STDATOMIC - Success
-- Found WrapAtomic: TRUE  
-- Found OpenGL: /Applications/Xcode.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX12.1.sdk/System/Library/Frameworks/OpenGL.framework   
-- Found WrapOpenGL: TRUE  
-- Configuring done
-- Generating done
-- Build files have been written to: /Users/me/Code/build-minimalSynthesizer-Qt_6_2_3_for_macOS-Debug
Elapsed time: 00:01.

Build output on Mac M1 (includes link errors)

14:12:57: Running steps for project minimalSynthesizer...
14:12:57: Persisting CMake state...
14:12:58: Starting: "/Users/me/Qt/Tools/CMake/CMake.app/Contents/bin/cmake" --build /Users/me/Code/build-minimalSynthesizer-Qt_6_2_3_for_macOS-Debug --target appSynth
[  3%] Built target appSynth_tooling
[  7%] Automatic MOC for target Synth
[  7%] Built target Synth_autogen
[ 10%] Running AUTOMOC file extraction for target Synth
[ 10%] Built target Synth_automoc_json_extraction
[ 14%] Running moc --collect-json for target Synth
[ 17%] Automatic QML type registration for target Synth
[ 21%] Running rcc for resource qmake_Synth
Consolidate compiler generated dependencies of target Synth
[ 25%] Building CXX object CMakeFiles/Synth.dir/Synth_autogen/mocs_compilation.cpp.o
[ 28%] Building CXX object CMakeFiles/Synth.dir/synth_qmltyperegistrations.cpp.o
[ 32%] Building CXX object CMakeFiles/Synth.dir/.rcc/qrc_qmake_Synth.cpp.o
[ 35%] Building CXX object CMakeFiles/Synth.dir/Synthesizer.cpp.o
[ 39%] Linking CXX shared library libSynth.dylib
Undefined symbols for architecture arm64:
  "QAudioSink::stop()", referenced from:
      Synthesizer::stop() in Synthesizer.cpp.o
  "QAudioSink::start(QIODevice*)", referenced from:
      Synthesizer::startPull(QIODevice*) in Synthesizer.cpp.o
  "QAudioSink::QAudioSink(QAudioFormat const&, QObject*)", referenced from:
      Synthesizer::startPull(QIODevice*) in Synthesizer.cpp.o
ld: symbol(s) not found for architecture arm64
clang: error: linker command failed with exit code 1 (use -v to see invocation)
make[3]: *** [libSynth.dylib] Error 1
make[2]: *** [CMakeFiles/Synth.dir/all] Error 2
make[1]: *** [CMakeFiles/appSynth.dir/rule] Error 2
make: *** [appSynth] Error 2
14:13:00: The process "/Users/me/Qt/Tools/CMake/CMake.app/Contents/bin/cmake" exited with code 2.
Error while building/deploying project minimalSynthesizer (kit: Qt 6.2.3 for macOS)
When executing step "Build"
14:13:00: Elapsed time: 00:02.

CMake output on Windows 10

Logging in and fetching licenses ...
Checking for updated license succeeded (3 licenses fetched)
Running C:\Qt\Tools\CMake_64\bin\cmake.exe -S C:/Users/me/OneDrive/Documents/Code/OMI-experiments/minimalSynthesizer -B C:/Users/me/OneDrive/Documents/Code/OMI-experiments/build-minimalSynthesizer-Desktop_Qt_6_2_3_MSVC2019_64bit-Debug "-DCMAKE_GENERATOR:STRING=Ninja" "-DCMAKE_BUILD_TYPE:STRING=Debug" "-DCMAKE_PROJECT_INCLUDE_BEFORE:FILEPATH=C:/Qt/Tools/QtCreator/share/qtcreator/package-manager/auto-setup.cmake" "-DQT_QMAKE_EXECUTABLE:STRING=C:/Qt/6.2.3/msvc2019_64/bin/qmake.exe" "-DCMAKE_PREFIX_PATH:STRING=C:/Qt/6.2.3/msvc2019_64" "-DCMAKE_C_COMPILER:STRING=C:/Program Files/Microsoft Visual Studio/2022/Community/VC/Tools/MSVC/14.30.30705/bin/HostX64/x64/cl.exe" "-DCMAKE_CXX_COMPILER:STRING=C:/Program Files/Microsoft Visual Studio/2022/Community/VC/Tools/MSVC/14.30.30705/bin/HostX64/x64/cl.exe" in C:\Users\me\OneDrive\Documents\Code\OMI-experiments\build-minimalSynthesizer-Desktop_Qt_6_2_3_MSVC2019_64bit-Debug.
-- The CXX compiler identification is MSVC 19.30.30706.0
-- Detecting CXX compiler ABI info
-- Detecting CXX compiler ABI info - done
-- Check for working CXX compiler: C:/Program Files/Microsoft Visual Studio/2022/Community/VC/Tools/MSVC/14.30.30705/bin/HostX64/x64/cl.exe - skipped
-- Detecting CXX compile features
-- Detecting CXX compile features - done
-- Looking for C++ include pthread.h
-- Looking for C++ include pthread.h - not found
-- Found Threads: TRUE  
-- Performing Test HAVE_STDATOMIC
-- Performing Test HAVE_STDATOMIC - Success
-- Found WrapAtomic: TRUE  
-- Could NOT find WrapVulkanHeaders (missing: Vulkan_INCLUDE_DIR) 
-- Could NOT find WrapVulkanHeaders (missing: Vulkan_INCLUDE_DIR) 
-- Configuring done
-- Generating done
-- Build files have been written to: C:/Users/me/OneDrive/Documents/Code/OMI-experiments/build-minimalSynthesizer-Desktop_Qt_6_2_3_MSVC2019_64bit-Debug
Elapsed time: 00:07.

Build output on Windows 10 (includes link errors)

21:02:05: Running steps for project minimalSynthesizer...
21:02:05: Starting: "C:\Qt\Tools\CMake_64\bin\cmake.exe" --build C:/Users/me/OneDrive/Documents/Code/OMI-experiments/build-minimalSynthesizer-Desktop_Qt_6_2_3_MSVC2019_64bit-Debug --target appSynth
[1/25 0.9/sec] Automatic MOC for target Synth
[2/25 1.8/sec] Running AUTOMOC file extraction for target Synth
[3/25 2.6/sec] Running moc --collect-json for target Synth
[4/25 1.8/sec] Automatic QML type registration for target Synth
[5/25 1.9/sec] Building CXX object CMakeFiles\Synth.dir\.rcc\qrc_qmake_Synth.cpp.obj
[6/25 1.5/sec] Building CXX object CMakeFiles\Synth.dir\Synth_autogen\mocs_compilation.cpp.obj
[7/25 1.7/sec] Building CXX object CMakeFiles\Synth.dir\Synthesizer.cpp.obj
[8/25 1.7/sec] Building CXX object CMakeFiles\Synth.dir\synth_qmltyperegistrations.cpp.obj
[9/25 1.2/sec] Linking CXX shared library Synth.dll
FAILED: Synth.dll Synth.lib 
cmd.exe /C "cd . && C:\Qt\Tools\CMake_64\bin\cmake.exe -E vs_link_dll --intdir=CMakeFiles\Synth.dir --rc=C:\PROGRA~2\WI3CF2~1\10\bin\100190~1.0\x64\rc.exe --mt=C:\PROGRA~2\WI3CF2~1\10\bin\100190~1.0\x64\mt.exe --manifests  -- C:\PROGRA~1\MICROS~1\2022\COMMUN~1\VC\Tools\MSVC\1430~1.307\bin\Hostx64\x64\link.exe /nologo CMakeFiles\Synth.dir\Synth_autogen\mocs_compilation.cpp.obj CMakeFiles\Synth.dir\synth_qmltyperegistrations.cpp.obj CMakeFiles\Synth.dir\.rcc\qrc_qmake_Synth.cpp.obj CMakeFiles\Synth.dir\Synthesizer.cpp.obj  /out:Synth.dll /implib:Synth.lib /pdb:Synth.pdb /dll /version:0.0 /machine:x64 /debug /INCREMENTAL  C:\Qt\6.2.3\msvc2019_64\lib\Qt6Qmld.lib  C:\Qt\6.2.3\msvc2019_64\lib\Qt6Networkd.lib  C:\Qt\6.2.3\msvc2019_64\lib\Qt6Cored.lib  mpr.lib  userenv.lib  ws2_32.lib  shell32.lib  kernel32.lib user32.lib gdi32.lib winspool.lib shell32.lib ole32.lib oleaut32.lib uuid.lib comdlg32.lib advapi32.lib  && cd ."
LINK Pass 1: command "C:\PROGRA~1\MICROS~1\2022\COMMUN~1\VC\Tools\MSVC\1430~1.307\bin\Hostx64\x64\link.exe /nologo CMakeFiles\Synth.dir\Synth_autogen\mocs_compilation.cpp.obj CMakeFiles\Synth.dir\synth_qmltyperegistrations.cpp.obj CMakeFiles\Synth.dir\.rcc\qrc_qmake_Synth.cpp.obj CMakeFiles\Synth.dir\Synthesizer.cpp.obj /out:Synth.dll /implib:Synth.lib /pdb:Synth.pdb /dll /version:0.0 /machine:x64 /debug /INCREMENTAL C:\Qt\6.2.3\msvc2019_64\lib\Qt6Qmld.lib C:\Qt\6.2.3\msvc2019_64\lib\Qt6Networkd.lib C:\Qt\6.2.3\msvc2019_64\lib\Qt6Cored.lib mpr.lib userenv.lib ws2_32.lib shell32.lib kernel32.lib user32.lib gdi32.lib winspool.lib shell32.lib ole32.lib oleaut32.lib uuid.lib comdlg32.lib advapi32.lib /MANIFEST /MANIFESTFILE:CMakeFiles\Synth.dir/intermediate.manifest CMakeFiles\Synth.dir/manifest.res" failed (exit code 1120) with the following output:
   Creating library Synth.lib and object Synth.exp
Synthesizer.cpp.obj : error LNK2019: unresolved external symbol "__declspec(dllimport) public: __cdecl QAudioSink::QAudioSink(class QAudioFormat const &,class QObject *)" (__imp_??0QAudioSink@@QEAA@AEBVQAudioFormat@@PEAVQObject@@@Z) referenced in function "public: void __cdecl Synthesizer::startPull(class QIODevice *)" (?startPull@Synthesizer@@QEAAXPEAVQIODevice@@@Z)
Synthesizer.cpp.obj : error LNK2019: unresolved external symbol "__declspec(dllimport) public: virtual __cdecl QAudioSink::~QAudioSink(void)" (__imp_??1QAudioSink@@UEAA@XZ) referenced in function "public: virtual void * __cdecl QAudioSink::`scalar deleting destructor'(unsigned int)" (??_GQAudioSink@@UEAAPEAXI@Z)
Synthesizer.cpp.obj : error LNK2019: unresolved external symbol "__declspec(dllimport) public: void __cdecl QAudioSink::start(class QIODevice *)" (__imp_?start@QAudioSink@@QEAAXPEAVQIODevice@@@Z) referenced in function "public: void __cdecl Synthesizer::startPull(class QIODevice *)" (?startPull@Synthesizer@@QEAAXPEAVQIODevice@@@Z)
Synthesizer.cpp.obj : error LNK2019: unresolved external symbol "__declspec(dllimport) public: void __cdecl QAudioSink::stop(void)" (__imp_?stop@QAudioSink@@QEAAXXZ) referenced in function "public: void __cdecl Synthesizer::stop(void)" (?stop@Synthesizer@@QEAAXXZ)
Synthesizer.cpp.obj : error LNK2001: unresolved external symbol "public: virtual struct QMetaObject const * __cdecl QAudioSink::metaObject(void)const " (?metaObject@QAudioSink@@UEBAPEBUQMetaObject@@XZ)
Synthesizer.cpp.obj : error LNK2001: unresolved external symbol "public: virtual void * __cdecl QAudioSink::qt_metacast(char const *)" (?qt_metacast@QAudioSink@@UEAAPEAXPEBD@Z)
Synthesizer.cpp.obj : error LNK2001: unresolved external symbol "public: virtual int __cdecl QAudioSink::qt_metacall(enum QMetaObject::Call,int,void * *)" (?qt_metacall@QAudioSink@@UEAAHW4Call@QMetaObject@@HPEAPEAX@Z)
Synth.dll : fatal error LNK1120: 7 unresolved externals
ninja: build stopped: subcommand failed.
21:02:13: The process "C:\Qt\Tools\CMake_64\bin\cmake.exe" exited with code 1.
Error while building/deploying project minimalSynthesizer (kit: Desktop Qt 6.2.3 MSVC2019 64bit)
When executing step "Build"
21:02:13: Elapsed time: 00:08.

CMakeList.txt

cmake_minimum_required(VERSION 3.16)

project(minimalSynthesizer VERSION 0.1 LANGUAGES CXX)

set(CMAKE_AUTOMOC ON)
set(CMAKE_CXX_STANDARD_REQUIRED ON)

find_package(Qt6 6.2 COMPONENTS Quick Multimedia REQUIRED)

qt_add_executable(appSynth
    main.cpp
)

qt_add_qml_module(appSynth
    URI minimalSynthesizer
    VERSION 1.0
    QML_FILES main.qml
)

qt_add_qml_module(Synth
    URI Synth
    VERSION 1.0
    SOURCES
        Synthesizer.h Synthesizer.cpp
)
target_include_directories(Synthplugin
     PUBLIC ${CMAKE_CURRENT_SOURCE_DIR}
)

target_compile_definitions(appSynth
    PRIVATE $<$<OR:$<CONFIG:Debug>,$<CONFIG:RelWithDebInfo>>:QT_QML_DEBUG>)
target_link_libraries(appSynth
    PRIVATE Qt6::Quick Qt6::Multimedia
    Synth
)

Synthesizer.h

#pragma once

#include <QObject>
#include <QtMultimedia/QAudioFormat>
#include <QtMultimedia/QAudioSink>

class Synthesizer : public QObject
{
    Q_OBJECT

public:
    explicit Synthesizer(const QAudioFormat &format, QObject *parent = nullptr);
    virtual ~Synthesizer();

    void startPull(QIODevice *device);
    void stop();

private:
    QAudioFormat _audioFormat;
    QAudioSink *_audioSink;
};

Synthesizer.cpp

#include "Synthesizer.h"

Synthesizer::Synthesizer(const QAudioFormat &format, QObject *parent)
    : QObject{parent}
    , _audioFormat(format)
    , _audioSink(nullptr)
{
}

Synthesizer::~Synthesizer()
{
    stop();
}

void Synthesizer::startPull(QIODevice *device)
{
    stop();

    _audioSink = new QAudioSink(_audioFormat);
    _audioSink->start(device);
}

void Synthesizer::stop()
{
    if (_audioSink == nullptr)
        return;

    _audioSink->stop();
    _audioSink->deleteLater();
    _audioSink = nullptr;
}

main.cpp (default for Qt Quick project)

#include <QGuiApplication>
#include <QQmlApplicationEngine>


int main(int argc, char *argv[])
{
    QGuiApplication app(argc, argv);

    QQmlApplicationEngine engine;
    const QUrl url(u"qrc:/minimalSynthesizer/main.qml"_qs);
    QObject::connect(&engine, &QQmlApplicationEngine::objectCreated,
                     &app, [url](QObject *obj, const QUrl &objUrl) {
        if (!obj && url == objUrl)
            QCoreApplication::exit(-1);
    }, Qt::QueuedConnection);
    engine.load(url);

    return app.exec();
}

main.qml (default for Qt Quick project)

import QtQuick

Window {
    width: 640
    height: 480
    visible: true
    title: qsTr("Hello World")
}

paulmasri

OK I'm a bit closer, but I don't have a solution.

Within qt_add_qml_module, you have to include all SOURCE classes/functions that are used.

For example, if I made my Synthesizer class depend on another class, AudioMakers then the source (AudioMakers.h & AudioMakers.cpp) must be in the SOURCE list and omitting them gives the same errors.

If I just include the headers of dependant classes/functions (i.e. AudioMakers.h) then I get a different bunch of messages that mean "Hey the definitions are missing for some declarations!"

So there must be a way of creating a QML module and letting it know where to find referenced functions without having to include them within SOURCE. Any ideas?

SGaist

Sorry, I lost track on this one.

What is the status now ?

paulmasri

@SGaist Still stuck. And still a blocking issue for my project.

I've worked out that the errors are not platform/CPU specific. They're about dependencies.

Synthesizer depends on classes/functions not in the QML module. I've created this question about the general case (where the classes/functions it is dependent on are elsewhere within the project) — no responses as yet.

And this thread is about the specific case where those dependencies are in a Qt module.

It would be great to get solutions to both questions, if you're able (or can loop in the right person at Qt).

SGaist

@paulmasri said in CMake: a QML module that uses QtMultimedia (or other Qt non-core module):

qt_add_qml_module(Synth
URI Synth
VERSION 1.0
SOURCES
Synthesizer.h Synthesizer.cpp
)

Shouldn't that be Synthplugin ?

With an additional:

target_link_libraries(Synthplugin
    PRIVATE Qt6::Quick Qt6::Multimedia
)

?

paulmasri

@SGaist Yes it should have been target_link_libraries(Synthplugin... (and I did end up testing that myself though I didn't post about it). It makes no difference. It still doesn't solve it.

SGaist

Did you add:

target_link_libraries(Synthplugin
    PRIVATE Qt6::Quick Qt6::Multimedia
)

to you CMakeLists.txt ?

paulmasri

@SGaist Looks like we were writing our last messages at the same time. Yes I did try exactly that and it makes no difference.

I note that the documentation for qt_add_qml_module has optional keywords DEPENDENCIES and IMPORTS but there are no examples and the descriptions aren't clear about how/whether they could be used for a module like QtMultimedia.

Croitor Alexandru

DEPENDENCIES is only relevant for resolving dependencies between QML modules at runtime, or for tools like qmllint.
It does not affect linking relationships at all.

I suggest you push your current project state to some repository (like github) and share it and the errors you get, because it's not entirely clear what fails at the moment.

For example in your post at https://forum.qt.io/post/711286 you link Qt6::Multimedia into appSynth rather than Synth.

To ensure Multimedia symbols are found, you need to link Qt6::Multimedia into the target whose sources uses multimedia symbols.

Within qt_add_qml_module, you have to include all SOURCE classes/functions that are used.
For example, if I made my Synthesizer class depend on another class, AudioMakers then the source (AudioMakers.h & AudioMakers.cpp) must be in the SOURCE list and omitting them gives the same errors.

I'm not sure I understand this statement.
All sources both (.cpp and .h) should indeed be specified as sources. either via qt_add_qml_module's SOURCES option or using target_sources.