In the qml video example (https://doc.qt.io/qt-6/qtmultimedia-video-qmlvideo-example.html)

The URI name in CMake and the used import module name have inconsistent upper and lower case usage. 

in qmlvideo/frequencymonitor/CMakeLists.txt:
qt_add_qml_module(frequencymonitor
    URI frequencymonitor
    QML_FILES
        "FrequencyItem.qml"
)

in frequencymonitor/FrequencyItem.qml:

import FrequencyMonitor 1.0

in qmlvideo/Content.qml

import frequencymonitor

When running the app, clicking on the buttons, it shows the error:

qrc:/qt/qml/frequencymonitor/FrequencyItem.qml:5:1: module "frequencymonitor" version 1.0 is not installed

All 3 places should be changed to FrequencyMonitor