Matlab ignores my videoReader command

I am trying to read a video from 4 seconds in. I use this:

v = VideoReader('IMG_3557.MOV','CurrentTime',4); % read video file

But when I do ths:

numbframes = v.NumFrames;

I get the same number of frames as the entire video from the beginning. I'm not sure what I'm doing wrong. Thanks

[Geoff Hayes]

Chidiebere - since the number of frames are the same, does that mean the duration is the same too? For example, what is

duration = v.Duration;

for the full video and the full video less the four seconds?

[Chidiebere Brendan Obiechefu]

Yeah it gives me same duration as well which I also don’t get. The video is 30fps so I expected to see numframes less by 120.

[Steven Lord]

Just because you're skipping over the frames doesn't mean the file has fewer frames.

Answer 1

[Steven Lord]

Have you read the data from the VideoReader or have you just created the object?

If I open to page 23 of a 345 page long book but then ask how many pages the book has, I'll have to flip to the last page to get the answer 345.

If I ask the question how many pages do I still have to read, one way to do that is to read the pages one by one and count each page as I read it.

I think the "Read Video Using Frame Index and Time Interchangeably" example on the documentation page does something like what you're trying to do.

[Chidiebere Brendan Obiechefu]

Ahh this explains it. Thank you!