Performance Discrepancy between Picamera2 and libcamera-vid

[SebZachrau]

I'm experiencing a significant performance discrepancy between using Picamera2 and directly using libcamera-vid. I'm hoping to understand why this is happening and how I can achieve similar performance with Picamera2.

Using Picamera2, I'm only achieving about 10 FPS with the following code:

import cv2
import time
from picamera2 import Picamera2

picam2 = Picamera2()

config = picam2.create_video_configuration(
    main={"size": (2028, 1520), "format": "RGB888"},
    raw={"size": (4056, 3040), "format": "SRGGB12_CSI2P"},
    controls={"FrameDurationLimits": (24993, 24993)}  # ~40 fps
)
picam2.configure(config)
picam2.start()

while True:
    frame = picam2.capture_array()
    cv2.imshow("Camera", frame)
    if cv2.waitKey(1) & 0xFF == ord('q'):
        break

picam2.stop()
cv2.destroyAllWindows()

However, my sensor modes indicate that I should be able to achieve 40 FPS:

Copy
{'bit_depth': 12,
 'crop_limits': (0, 0, 4056, 3040),
 'exposure_limits': (60, 674181621, None),
 'format': SRGGB12_CSI2P,
 'fps': 40.01,
 'size': (2028, 1520),
 'unpacked': 'SRGGB12'}

Interestingly, when I use libcamera-vid directly through a subprocess, I can achieve 30 FPS:

import subprocess

def run_libcamera_vid():
    cmd = [
        "libcamera-vid",
        "-t", "0",
        "--width", "4056",
        "--height", "3040",
        "--framerate", "30",
        "--codec", "mjpeg",
        "-o", "-"
    ]
    process = subprocess.Popen(cmd, stdout=subprocess.PIPE, stderr=subprocess.PIPE)
    return process

process = run_libcamera_vid()

while True:
    frame = process.stdout.read(4056 * 3040 * 3)
    if not frame:
        break

process.wait()

My questions are:

Why is there such a large performance gap between Picamera2 and directly using libcamera-vid?
Are there any optimizations or configurations I can apply to my Picamera2 code to achieve similar performance to libcamera-vid?
Is this performance difference expected, or could there be an issue with my setup or code?
Any insights or suggestions would be greatly appreciated. Thank you!