2.5.24 IDeckLinkScreenPreviewCallback Interface

The IDeckLinkScreenPreviewCallback interface is a callback class which is called to facilitate updating of an on-screen preview of a video stream being played or captured.

An object with the IDeckLinkScreenPreviewCallback interface may be registered as a callback with the IDeckLinkInput or IDeckLinkOutput interfaces.

Tip

During playback or capture, frames will be delivered to the preview callback. A dedicated preview thread waits for the next available frame before calling the callback. The frame delivery rate may be rate limited by the preview callback it is not required to maintain full frame rate and missing frames in preview will have no impact on capture or playback.

Related Interfaces

Interface

Interface ID

Description

IDeckLinkOutput

IID_IDeckLinkOutput

An IDeckLinkScreenPreviewCallback object interface is registered with IDeckLinkOutput::SetScreenPreviewCallback()

IDeckLinkInput

IID_IDeckLinkInput

An IDeckLinkScreenPreviewCallback object interface is registered with IDeckLinkInput::SetScreenPreviewCallback()

IDeckLinkVideoFrame

IID_IDeckLinkVideoFrame

An IDeckLinkVideoFrame object interface is provided for rendering by IDeckLinkScreenPreviewCallback::DrawFrame()

IDeckLinkCocoaScreenPreviewCallback

IID_IDeckLinkCocoaScreenPreviewCallback

IDeckLinkCocoaScreenPreviewCallback subclasses IDeckLinkScreenPreviewCallback

2.5.24.1 IDeckLinkScreenPreviewCallback::DrawFrame method

HRESULT IDeckLinkScreenPreviewCallback::DrawFrame(IDeckLinkVideoFrame *theFrame);

The DrawFrame method is called by a dedicated preview thread delivering video frames while the scheduled playback is running. The return value (required by COM) is ignored by the caller.

Note

If the frame to be drawn to the preview hasn’t changed since the last time the callback was called, the frame parameter will be NULL.

Parameters:

theFrame – Video frame to preview