I’m using OpenCV’s cv::VideoCapture in C++ (or Python) to connect to a camera stream. I would like to know if OpenCV internally uses multithreading or multiprocessing when opening and capturing frames from the camera.
Specifically, I’m curious about:
- Whether OpenCV spawns new threads or processes when using cv::VideoCapture.
- If FFmpeg is enabled as the backend, does it use multithreading or multiprocessing under the hood?
- How can I verify the threading or process behavior during camera streaming?
What I Tried:
I checked the current process using psutil (in Python) and printed the number of threads:
<code>import cv2
import psutil
cap = cv2.VideoCapture("rtsp://camera_stream", cv2.CAP_FFMPEG)
process = psutil.Process()
print(f"Process ID: {process.pid}, Name: {process.name()}")
print(f"Thread count: {process.num_threads()}")
for thread in process.threads():
print(f"Thread ID: {thread.id}, CPU Time: {thread.user_time + thread.system_time}")
cap.release()
</code>
<code>import cv2
import psutil
cap = cv2.VideoCapture("rtsp://camera_stream", cv2.CAP_FFMPEG)
process = psutil.Process()
print(f"Process ID: {process.pid}, Name: {process.name()}")
print(f"Thread count: {process.num_threads()}")
for thread in process.threads():
print(f"Thread ID: {thread.id}, CPU Time: {thread.user_time + thread.system_time}")
cap.release()
</code>
import cv2
import psutil
cap = cv2.VideoCapture("rtsp://camera_stream", cv2.CAP_FFMPEG)
process = psutil.Process()
print(f"Process ID: {process.pid}, Name: {process.name()}")
print(f"Thread count: {process.num_threads()}")
for thread in process.threads():
print(f"Thread ID: {thread.id}, CPU Time: {thread.user_time + thread.system_time}")
cap.release()
- Does VideoCapture use multithreading or multiprocessing internally?
- Is there a reliable way to verify whether the underlying backend (e.g., FFmpeg) has enabled multithreading?
- Are there specific settings in OpenCV or FFmpeg that can control this behavior?
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