Accessing a frame using the videoReader is not accurate

[agirbau]

This is just to point out this issue in OpenCV (as mmcv is using OpenCV to read the frames in a video).

TL;DR:
when doing

video = mmcv.VideoReader(video_path)
frame = video[frame_num]

there are chances of getting the wrong frame (sometimes by a huge margin) as output.

[zhouzaida]

Thanks for your feedback, we will fix it.

[makecent]

There are some codes in mmcv.VideoReader saying corrects the position. Does it mean this issue was resolved, or they are unrelated?

Even worse, the num of frames generated from enumerate(Videoreader) is NOT equal to (normally less than) the attribute Videoreader._frame_cnt.