CODEWITHSUNDEEP
c++videocameraframedirectshow
vyndor
vyndor

Reputation: 368

Read frame by request with DirectShow

I'm trying to use DirectShow to capture video from webcam. I assume to use SampleGabber class. For now I see that DirectShow can only read frames continiously with some desired fps. Can DirectShow read frames by request?

Upvotes: 1

Views: 687

Answers (1)

Roman Ryltsov
Roman Ryltsov

Reputation: 69652

DirectShow pipeline sets up streaming video. Frames will continuously stream through Sample Grabber and its callback, if you set it up. The callback itself adds minimal processing overhead if you don't force format change (to force video to be RGB in particular). It is up to whether to process or skip a frame there.

On request grabbing will be taking either last known video frame streamed, or next to go through Sample Grabber. This is typical mode of operation.

Some devices offer additional feature of taking a still on request. This is a rarer case and it's described on MSDN here: Capturing an Image From a Still Image Pin:

Some cameras can produce a still image separate from the capture stream, and often the still image is of higher quality than the images produced by the capture stream. The camera may have a button that acts as a hardware trigger, or it may support software triggering. A camera that supports still images will expose a still image pin, which is pin category PIN_CATEGORY_STILL.

The recommended way to get still images from the device is to use the Windows Image Acquisition (WIA) APIs. [...]

To trigger the still pin, use [...]

Upvotes: 1

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