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Render Video

In this tutorial, you will learn how to render a video.

Preface​

In order to render a video we need:

  • an element (HTMLDivElement) to use as the container for the viewport
  • the URL to the video.
  • a server that will serve the video as MP4 using byte range requests
  • ideally, the video in 'fast start' format

Implementation​

We have already stored images on a server for the purpose of this tutorial.

First let's create an HTML element and style it to look like a viewport.

const content = document.getElementById('content');
const element = document.createElement('div');

element.style.width = '500px';
element.style.height = '500px';

content.appendChild(element);

Next, we need a renderingEngine and a viewport to render the images.

const renderingEngineId = 'myRenderingEngine';
const renderingEngine = new RenderingEngine(renderingEngineId);

We can then create a viewport inside the renderingEngine by using the enableElement API. Note that since we want to render a video, we have to specify the ViewportType.VIDEO.

const viewportId = 'CT_AXIAL_STACK';

const viewportInput = {
  viewportId,
  element,
  type: ViewportType.VIDEO,
};

renderingEngine.enableElement(viewportInput);

RenderingEngine will handle creation of the viewports, and we can get the viewport object and set the video URL on it, and choose the index of the image to be displayed.

const viewport = renderingEngine.getViewport(viewportId);

viewport.setVideoURL(
  'https://ohif-assets.s3.us-east-2.amazonaws.com/video/rendered.mp4'
);

viewport.render();
Tip

For a compliant DICOMweb server, the video will be available on the rendered endpoint. It may require an accept header to force it to be served in MP4 format if it is in MPEG2. It may not support either the fast start encoding or the byte range format, absence of which will prevent seeking through large videos. Small videos will likely be buffered entirely, so they can still seek.

For instance you can look at this example in OHIF which uses the rendered endpoint: https://d33do7qe4w26qo.cloudfront.net/dicomweb/studies/2.25.96975534054447904995905761963464388233/series/2.25.15054212212536476297201250326674987992/instances/2.25.179478223177027022014772769075050874231/rendered

Final code​

See examples/video/index.ts

Tip
  • Visit Examples page to see how to run the examples locally.
  • Check how to debug examples in the Debugging section.

Video Annotations

If the video viewport is instantiated with a setVideo call on an imageId with associated metadata, then it is possible to use annotations with the video viewport. These annotations will be shown on either a range of frames or a single frame, with some amount of time range allowed so that the annotation will actually be seen.

The annotationFrameRange class supports setting and retrieving time ranges on annotations. This is done by modifying the imageID in the /frames/<number> section or the frameNumber=<number> attribute. These become a range when the annotation applies to a range of values.

The frame range is automatically set when created to the current range being played on the video when the video is playing, or the frame number currently being displayed when not playing.