Qt Multimedia on WebAssembly

This page covers the availability of Qt Multimedia features on WebAssembly.

Limitations

Due to the asynchronous nature of javascript, some features such as getting the list of QMediaDevices, will not be readily available and may take some time to request permissions and gather the list of devices.

Playing video currently works by using an html 2d context, so all operations are on the CPU. This also means that only QGraphicsVideoItem/QGraphicsScene will work. There is no current support for QMultimediaWidgets / QVideoWidget which uses a webgl context to take processing onto the GPU.

Performance is acceptable, although there is a copy on every frame, so it may be less performant than desktop platforms when playing hi-def video.

Using and selecting different Codecs/video formats have not yet been tested, but whatever video formats the browser supports will most likely work.

Playing streaming bytes instead of a url. e.g. setSource(QIOStream) is also not currently supported. Some advanced features may or may not work at this time.

To setup playing a video file:

QMediaPlayer *player = new QMediaPlayer(this); QAudioOutput audioOutput; // chooses the default audio routing player->setAudioOutput(&audioOutput);

QGraphicsVideoItem *item = new QGraphicsVideoItem(); player->setVideoOutput(item);

QGraphicsScene *scene = new QGraphicsScene(this);

ui->graphicsView->setScene(scene); ui->graphicsView->scene()->addItem(item); ui->graphicsView->show();

and then to play the url:

player->setSource(QUrl(urlStr)); player->play();

Files can be served from the/any web server. Because of the restriction on local file storage, playing local files is discouraged.