Qt Video Replayer

Authors: Holoscan Team (NVIDIA)
Supported platforms: x86_64, aarch64
Last modified: March 18, 2025
Language: C++
Latest version: 1.0.0
Minimum Holoscan SDK version: 0.6.0
Tested Holoscan SDK versions: 0.6.0
Contribution metric: Level 1 - Highly Reliable

This application demonstrates how to integrate Holoscan with a Qt application. It support displaying the video frames output by a Holoscan operator and changing operator properties using Qt UI elements.

flowchart LR
    subgraph Holoscan application
        A[(VideoFile)] --> VideostreamReplayerOp
        VideostreamReplayerOp --> FormatConverterOp
        FormatConverterOp --> NppFilterOp
        NppFilterOp --> QtVideoOp
    end
    subgraph Qt Window
        QtVideoOp <-.-> QtHoloscanVideo
    end

The application uses the VideostreamReplayerOp to read from a file on disk, the FormatConverterOp to convert the frames from RGB to RGBA, the NppFilterOp to apply a filter to the frame and the QtVideoOp operator to display the video stream in a Qt window.

The QtHoloscanApp class, which extends the holoscan::Application class, is used to expose parameters of Holoscan operators as Qt properties.

For example the application uses a QML Checkbox is used the set the realtime property of the VideostreamReplayerOp operator.

    CheckBox {
        id: realtime
        text: "Use Video Framerate"
        checked: holoscanApp.realtime
        onCheckedChanged: {
            holoscanApp.realtime = checked;
        }
    }

The QtHoloscanVideo is a QQuickItem which can be use in the QML file. Multiple QtHoloscanVideo items can be placed in a Qt window.

import QtHoloscanVideo
Item {
    QtHoloscanVideo {
        objectName: "video"
    }
}

Run Instructions

This application requires Qt. For simplicity a DockerFile is available. To generate the container run:

./dev_container build --docker_file ./applications/qt_video_replayer/Dockerfile

The application can then be built by launching this container and using the provided run script.

./dev_container launch
./run build qt_video_replayer

Once the application is build it can be launched with the run script.

./run launch qt_video_replayer