MediaStreamSource.Starting | starting event

Applies to Windows and Windows Phone

Occurs when the MediaStreamSource is ready to start requesting MediaStreamSample objects. The event can specify a position in the media time-line from which the first MediaStreamSample should be delivered.


function onStarting(eventArgs) { /* Your code */ }
// addEventListener syntax
mediaStreamSource.addEventListener("starting", onStarting);
mediaStreamSource.removeEventListener("starting", onStarting);
- or -

mediaStreamSource.onstarting = onStarting;

Event information

Delegate TypedEventHandler<MediaStreamSource, MediaStreamSourceStartingEventArgs>


The MediaStreamSource raises this event before it starts requesting MediaStreamSamples for the first time. It also raises the event when it resumes requesting MediaStreamSamples after a Paused event has occurred.

Upon receiving this event, the application must invoke the SetActualStartPosition method on the MediaStreamSourceStartingRequest object to specify the actual position in the time-line from which MediaStreamSample objects will be retrieved.

This event cancels any SampleRequested events the application has not delivered the requested MediaStreamSample for. However, application must still invoke the Complete method on the MediaStreamSourceSampleRequestDeferral object for any previous SampleRequested events.

Applications are only required to have a handler for the Starting event if MediaStreamSource.CanSeek is set to true and they support seeking.


Minimum supported client

Windows 8.1

Minimum supported server

Windows Server 2012 R2

Minimum supported phone

Windows Phone 8.1 [Windows Phone Silverlight 8.1 and Windows Runtime apps]


Windows::Media::Core [C++]



See also




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