mismatch between calculated and reported Framerate using VideoReader

KV
2016 3 22
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更新时间：2016 3 23
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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.

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Matthew Eicholtz
Matthew Eicholtz 2016-3-22
I tried this with one of the built-in videos ('xylophone.mp4') and could not reproduce your error. Sorry.
KV
KV 2016-3-22
You think it may be related to a wmv file?
Matthew Eicholtz
Matthew Eicholtz 2016-3-22
I just tried it with a .wmv file I had on my machine and still had no problem.
Walter Roberson
Walter Roberson 2016-3-22
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
KV 2016-3-23
Yes, Walter -- the file does have variable frame rate. Is there any way I can get information about "timestamps" on a per-frame basis?

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2016-3-22

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