我正在尝试从视频文件中逐帧读取图像。视频文件放在当前目录中。试图提供视频文件的绝对路径仍然cat.isOpened()函数调用返回 false。此设置在 ubuntu 16.04 机器上，使用 pip3 安装了 opencv。
即使将这些标志cv2.CAP_FFMPEG、cv2.CAP_IMAGES 和 cv2.CAP_DSHOW作为 VideoCapture() 构造函数的第二个参数，isOPened() 也会返回 false。
有没有办法找出导致错误的原因？
import cv2
cap = cv2.VideoCapture('Megamind.avi')
if not cap.isOpened():
print("unable to open") # prints this
编辑 5：成功打开文件后，以下 strace 是否有意外情况。
$ strace python3 face_detect.py
......
......
open("Megamind.avi", O_RDONLY) = 3
fstat(3, {st_mode=S_IFREG|0664, st_size=1189270, ...}) = 0
read(3, "RIFF\216%\22\0AVI LISTr\"\0\0hdrlavih8\0\0\0"..., 4096) = 4096
lseek(3, 0, SEEK_CUR) = 4096
lseek(3, 0, SEEK_CUR) = 4096
lseek(3, 0, SEEK_CUR) = 4096
lseek(3, 0, SEEK_SET) = 0
read(3, "RIFF\216%\22\0AVI LISTr\"\0\0hdrlavih8\0\0\0"..., 4096) = 4096
lseek(3, 4096, SEEK_SET) = 4096
read(3, "\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0"..., 4096) = 4096
lseek(3, 1187840, SEEK_SET) = 1187840
read(3, "\16\0\351\3\0\00000dc\0\0\0\0F\331\16\0A\22\0\00001wb\20\0\0\0\220\353"..., 4096) = 1430
read(3, "", 4096) = 0
close(3) = 0
write(1, "unable to open\n", 15unable to open
) = 15
rt_sigaction(SIGINT, {SIG_DFL, [], SA_RESTORER, 0x7f33fcc27390}, {0x63df70, [], SA_RESTORER, 0x7f33fcc27390}, 8) = 0
futex(0x7f33f92f62bc, FUTEX_WAKE_OP_PRIVATE, 1, 1, 0x7f33f92f62b8, {FUTEX_OP_SET, 0, FUTEX_OP_CMP_GT, 1}) = 1
futex(0x7f33f92f6290, FUTEX_WAKE_PRIVATE, 1) = 1
futex(0x7f33f92f633c, FUTEX_WAKE_OP_PRIVATE, 1, 1, 0x7f33f92f6338, {FUTEX_OP_SET, 0, FUTEX_OP_CMP_GT, 1}) = 1
futex(0x7f33f92f6310, FUTEX_WAKE_PRIVATE, 1) = 1
futex(0x7f33f92f63bc, FUTEX_WAKE_OP_PRIVATE, 1, 1, 0x7f33f92f63b8, {FUTEX_OP_SET, 0, FUTEX_OP_CMP_GT, 1}) = 1
futex(0x7f33f92f6390, FUTEX_WAKE_PRIVATE, 1) = 1
munmap(0x7f33f42b8000, 33554432) = 0
munmap(0x7f33f1ab7000, 33554432) = 0
munmap(0x7f33ef276000, 33554432) = 0
exit_group(0) = ?
+++ exited with 0 +++