mismatch between calculated and reported Framerate using VideoReader

I am trying to process video data (wmv format) recorded using a standard consumer grade camera using Matlab (R2014a, on Linux/Ubuntu) using VideoReader

vr = VideoReader('my_movie_file.wmv')

frames = read(vr); % read all frames

size(frames, 4) % gives 4025

vr.NumberOfFrames % gives 4025

vr.Duration % gives 134.7950

vr.FrameRate % gives 15

Now, this does not compute!

I.e,

round(vr.FrameRate*vr.Duration) % gives  2022,

which is half the size of vr.NumberOfFrames -- which means that the reported FrameRate is 1/2 the "calculated" value!

What am I missing?? All help will be appreciated.

[Matthew Eicholtz]

I tried this with one of the built-in videos ('xylophone.mp4') and could not reproduce your error. Sorry.

[KV]

You think it may be related to a wmv file?

[Matthew Eicholtz]

I just tried it with a .wmv file I had on my machine and still had no problem.

[Walter Roberson]

Is the file variable framerate? If so then the reported framerate might be the last one in the file (the one in effect at the time you queried)

[KV]

Yes, Walter -- the file does have variable frame rate. Is there any way I can get information about "timestamps" on a per-frame basis?