一次在OpenCV中捕获来自两个摄像机的视频 [英] Capturing video from two cameras in OpenCV at once

问题描述

如何使用Python API使用OpenCV同时(或几乎)捕获两个或更多摄像机的视频?

How do you capture video from two or more cameras at once (or nearly) with OpenCV, using the Python API?

我有三个可以进行视频流传输的网络摄像头，分别位于/dev/video0，/dev/video1和/dev/video2.

I have three webcams, all capable of video streaming, located at /dev/video0, /dev/video1, and /dev/video2.

以教程为例，从单个图像中捕获图像相机很简单:

Using the tutorial as an example, capturing images from a single camera is simply:

import cv2
cap0 = cv2.VideoCapture(0)
ret0, frame0 = cap0.read()
cv2.imshow('frame', frame0)
cv2.waitKey()

这很好.

但是，如果我尝试初始化第二个摄像机，则尝试从它返回read()会返回None:

However, if I try to initialize a second camera, attempting to read() from it returns None:

import cv2
cap0 = cv2.VideoCapture(0)
cap1 = cv2.VideoCapture(1)
ret0, frame0 = cap0.read()
assert ret0 # succeeds
ret1, frame1 = cap1.read()
assert ret1 # fails?!

只是为了确保我不会意外给OpenCV一个不好的相机索引，所以我分别测试了每个相机索引，它们都可以独立工作.例如

Just to ensure I wasn't accidentally giving OpenCV a bad camera index, I tested each camera index individually and they all work by themselves. e.g.

import cv2
#cap0 = cv2.VideoCapture(0)
cap1 = cv2.VideoCapture(1)
#ret0, frame0 = cap0.read()
#assert ret0
ret1, frame1 = cap1.read()
assert ret1 # now it works?!

我在做什么错了?

我的硬件是运行Ubuntu的Macbook Pro.在Macbooks上专门研究了这个问题，我发现在OSX和不同类型的相机上也遇到了这个问题的其他人.如果我访问iSight，则代码中的两个调用都会失败.

My hardware is a Macbook Pro running Ubuntu. Researching the issue specifically on Macbooks, I've found others that have run into this problem too, both on OSX and with different types of cameras. If I access the iSight, both calls in my code fail.

推荐答案

是的，您肯定受到USB带宽的限制.尝试以全分辨率从两个设备读取数据时，您可能会遇到错误:

Yes you're definitely limited by the USB bandwidth. Attempting to read from both devices at full-rez you probably got error:

libv4l2: error turning on stream: No space left on device
VIDIOC_STREAMON: No space left on device
Traceback (most recent call last):
  File "p.py", line 7, in <module>
    assert ret1 # fails?!
AssertionError

然后将分辨率降低到160x120:

And then when you reduce the res to 160x120:

import cv2
cap0 = cv2.VideoCapture(0)
cap0.set(3,160)
cap0.set(4,120)
cap1 = cv2.VideoCapture(1)
cap1.set(3,160)
cap1.set(4,120)
ret0, frame0 = cap0.read()
assert ret0 # succeeds
ret1, frame1 = cap1.read()
assert ret1 # fails?!

现在看来可行！我敢打赌，两个摄像头都连接在同一USB卡上.您可以运行lsusb命令进行确认，并且它应该指示类似以下内容的内容:

now it seems to work! I bet you have both cams connected on the same USB card. You can run lsusb command to make sure, and it should indicate something like:

Bus 001 Device 006: ID 046d:081b Logitech, Inc. Webcam C310
Bus 001 Device 004: ID 0409:005a NEC Corp. HighSpeed Hub
Bus 001 Device 007: ID 046d:0990 Logitech, Inc. QuickCam Pro 9000
Bus 001 Device 005: ID 0409:005a NEC Corp. HighSpeed Hub
Bus 001 Device 003: ID 0409:005a NEC Corp. HighSpeed Hub
Bus 001 Device 002: ID 1058:0401 Western Digital Technologies, Inc. 
Bus 001 Device 001: ID 1d6b:0002 Linux Foundation 2.0 root hub
Bus 003 Device 001: ID 1d6b:0001 Linux Foundation 1.1 root hub
Bus 002 Device 001: ID 1d6b:0001 Linux Foundation 1.1 root hub

(请注意，两个摄像机都在同一总线上.)如果可能，您可以在机器上添加另一个USB卡以获取更多带宽.我之前已经这样做过，以便在一台机器上以全分辨率运行多个凸轮.尽管那是带有可用主板插槽的塔式工作站，但是不幸的是，您可能没有在MacBook笔记本电脑上使用该选项.

(Note both cameras on same bus.) If possible, you can add another USB card to your machine to gain more bandwidth. I've done this before in order to run multiple cams at full resolution on a single machine. Albeit that was a tower workstation with available motherboard slots, and unfortunately you may not have that option on a MacBook laptop.

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