问题
I have a camera on my linuxbox it is working well:
# $ ls -al /dev/video*
# crw-rw----+ 1 root video 81, 0 janv. 8 16:13 /dev/video0
# crw-rw----+ 1 root video 81, 1 janv. 8 16:13 /dev/video1
# $ groups
# adm cdrom sudo dip video plugdev lpadmin lxd sambashare docker libvirt
From python with cv2 it work well with the default driver CAP_V4L2
>>> from pathlib import Path
>>> import cv2
>>> print(cv2.VideoCapture(0, apiPreference=cv2.cv2.CAP_V4L2).isOpened())
True
>>>
I would like to access it with the FFMPEG driver (no success):
>>> print(cv2.VideoCapture(0, apiPreference=cv2.CAP_FFMPEG).isOpened())
False
>>>
From Python side the opencv look like to have the FFMPEG Driver:
>>> cv2.__version__
'4.4.0'
>>> info = cv2.getBuildInformation()
>>> video, parallel = info.index('Video'), info.index('Parallel')
>>> print(info[video:parallel])
Video I/O:
DC1394: NO
FFMPEG: YES
avcodec: YES (58.109.100)
avformat: YES (58.61.100)
avutil: YES (56.60.100)
swscale: YES (5.8.100)
avresample: NO
GStreamer: NO
v4l/v4l2: YES (linux/videodev2.h)
>>>
From Linux side look ok too:
$ dpkg -l |grep -i opencv
ii libopencv-core4.2:amd64 4.2.0+dfsg-5 amd64 computer vision core library
ii libopencv-imgcodecs4.2:amd64 4.2.0+dfsg-5 amd64 computer vision Image Codecs library
ii libopencv-imgproc4.2:amd64 4.2.0+dfsg-5 amd64 computer vision Image Processing library
ii libopencv-videoio4.2:amd64 4.2.0+dfsg-5 amd64 computer vision Video I/O library
$ dpkg -l |grep -i ffm
ii ffmpeg 7:4.2.4-1ubuntu0.1 amd64 Tools for transcoding, streaming and playing of multimedia files
ii gstreamer1.0-libav:amd64 1.16.2-2 amd64 ffmpeg plugin for GStreamer
ii libavcodec-extra:amd64 7:4.2.4-1ubuntu0.1 amd64 FFmpeg library with extra codecs (metapackage)
ii libavcodec-extra58:amd64 7:4.2.4-1ubuntu0.1 amd64 FFmpeg library with additional de/encoders for audio/video codecs
ii libavdevice58:amd64 7:4.2.4-1ubuntu0.1 amd64 FFmpeg library for handling input and output devices - runtime files
ii libavfilter7:amd64 7:4.2.4-1ubuntu0.1 amd64 FFmpeg library containing media filters - runtime files
ii libavformat58:amd64 7:4.2.4-1ubuntu0.1 amd64 FFmpeg library with (de)muxers for multimedia containers - runtime files
ii libavresample4:amd64 7:4.2.4-1ubuntu0.1 amd64 FFmpeg compatibility library for resampling - runtime files
ii libavutil56:amd64 7:4.2.4-1ubuntu0.1 amd64 FFmpeg library with functions for simplifying programming - runtime files
ii libffmpegthumbnailer4v5 2.1.1-0.2build2 amd64 shared library for ffmpegthumbnailer
ii libpostproc55:amd64 7:4.2.4-1ubuntu0.1 amd64 FFmpeg library for post processing - runtime files
ii libswresample3:amd64 7:4.2.4-1ubuntu0.1 amd64 FFmpeg library for audio resampling, rematrixing etc. - runtime files
ii libswscale5:amd64 7:4.2.4-1ubuntu0.1 amd64 FFmpeg library for image scaling and various conversions - runtime files
$
回答1:
Is FFMPEG used for capture from camera by OpenCV? I think it's for files (or streams), because VideoCapture is used both for camera and for files/streams.
On my Windows setup FFMPEG used as interface for capture from camera also doesn't work (but e.g. CAP_DSHOW works), while as a codec for files it reads a frame:
cap = cv2.VideoCapture("..\\ooo.mp4", apiPreference=cv2.CAP_FFMPEG) # OK
>>> print(cv2.VideoCapture(0, apiPreference=cv2.CAP_FFMPEG).isOpened())
False
>>> print(cv2.VideoCapture(0, apiPreference=cv2.CAP_DSHOW).isOpened())
True
import cv2
# cap = cv2.VideoCapture(0, apiPreference=cv2.CAP_FFMPEG) # prints "ERROR"
cap = cv2.VideoCapture(0, apiPreference=cv2.CAP_DSHOW) # OK, shows an image
ret, fr = cap.read()
if ret: cv2.imshow("FR", fr)
else: print("ERROR")
cv2.waitKey(0)
See also: https://trac.ffmpeg.org/wiki/Capture/Webcam
"Linux
Uses the video4linux2 (or simply v4l2) input device to capture live input such as from a webcam. See the v4l2 input device documentation for more information. "
For Windows FFMPEG is mentioned to use DirectShow as in my test:
>Windows
>dshow
>
>Uses the dshow (DirectShow) input device which is the preferred option for
>Windows users.
来源:https://stackoverflow.com/questions/65641483/how-to-make-work-opencv-with-ffmpeg-driver