c++ - 使用 DirectShow 按请求读取帧

Question

我正在尝试使用 DirectShow 从网络摄像头捕捉视频。我假设使用 SampleGabber 类。现在我看到 DirectShow 只能以某些所需的 fps 连续读取帧。 DirectShow 可以按请求读取帧吗？

Answer 1

DirectShow 管道设置流式视频。如果您进行了设置，帧将连续流过 Sample Grabber 及其回调。如果您不强制更改格式(特别是强制视频为 RGB)，则回调本身会增加最小的处理开销。这取决于是否处理或跳过那里的帧。

根据请求，抓取将采用流式传输的最后一个已知视频帧，或下一个通过 Sample Grabber 进行的抓取。这是典型的操作模式。

一些设备提供额外的功能，可以根据要求拍摄静止图像。这是一种罕见的情况，MSDN 上对其进行了描述: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 [...]