How to Overcome Lag in OpenCV VideoCapture Caused by Capture Buffer Accumulation?

OpenCV VideoCapture Lag Induced by Capture Buffer

You have encountered a lag issue with OpenCV's VideoCapture due to the accumulation of frames in the capture buffer. As a workaround, you have resorted to reading the buffer at 30fps to clear it quickly.

OpenCV Solution

OpenCV provides a way to set the buffer size manually:

<code class="cpp">cv::VideoCapture cap;
cap.set(CV_CAP_PROP_BUFFERSIZE, 3); // store only 3 frames</code>

However, this solution is only supported by the DC1394 v 2.x backend.

Hackaround 1

An alternative approach is to measure the time it takes to retrieve a frame:

• If the time is short, the frame is from the buffer and can be discarded.
• Repeat until the time exceeds a threshold, indicating the buffer is empty.

Hackaround 2

You can create a third thread that continuously grabs frames at a high speed using cv::VideoCapture.grab() to keep the buffer empty. Synchronize access between this thread and your worker thread using a spin-lock.

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