Dot name reference on non-scalar structure using Video Reader class

Hi... I am trying to read in a .wmv. I have basically copied the example from the VideoReader class in the help but I get this error when I run the .m:

Dot name reference on non-scalar structure.

Error in VideoReader/read (line 91)

    if( ~isempty(obj.NumberOfFrames) )

Error in vidFile (line 22)

    mov(i).cdata = read(Test, i);

mov is a 1xNumberOfFrames struct with objects 'cdata' and 'colormap'. The main issue is number frames it reads before this error is thrown varies.

Please help. I have banged my head against the wall enough...

Answer 1

[Ralph Hummeling]

@Townsend:

I'm afraid you've stumbled upon a bug that persists since R2012a. Matlab sometimes erroneously interprets a scalar structure as being non-scalar when confronted with a getfield operation: S.fieldname

A workaround is to insert an index on the field reference like this: S(1).fieldname

It's ugly but it works. So in your case your code could read: if( ~isempty(obj(1).NumberOfFrames) )

[Daniel Shub]

Do you have a link to the bug report? This seems like it could potentially cause a huge amount of code to break.

[Ralph Hummeling]

@Daniel:

Indeed, this bug has a large impact on existing code and I've submitted a Service Request. If they can't resolve I'll file a bug;-)

[Townsend]

@Ralph

I have tried adding an index like you suggested but I do not have access to save the "new" read function (from VideoReader class). So I then save it locally and then I get this error.

Error using message/getString
Incorrect number of parameters supplied for 'MATLAB:class:MethodRestricted'. Expected 2 but
found 1.

Error in VideoReader.handleImplException (line 357)
            throwAsCaller(MException(implException.identifier, msgObj.getString));

Error in vidFile>read (line 108)
    VideoReader.handleImplException(err);

Error in vidFile (line 16)
   mov(k).cdata=read(obj,k);

Error in dataFile (line 78)
[nFrames, rFrames, Duration, Format, vWidth, vHeight, hf, mov] = vidFile(vid_file);

I have tried to find out how to by pass this but it is above my coding knowledge and the examples I find don't make sense to me. I guess I am not as familiar with matlab as originally thought.

Thanks for you help in advance.

[Ralph Hummeling]

@Townsend

If you're still coping with this bug send me your script and I'll see what I can do. Which Matlab release are you using, I can't find any recent release with the code you supplied?

Check my website to contact me: www.hummeling.com

[Bryan]

@Ralph

I have a very similar issue to Townsend's, and am disappointed to learn it's a MATLAB bug! For some reason the read() function works for the first 40 or so frames of my video, then throws an error after that. I also am not able to edit the MATLAB read() function. I'm using the R2012b release -- any help would be greatly appreciated.

Bryan

[Florence Yellin]

Has anybody resolved this issue? I am having the same problem.

Thanks! Flori

[Image Analyst]

You can search for VideoReader bugs here. Click that link, then scroll down.

[William Summers]

Thanks!

[Falak Shah]

Having a similar problem in 2012b.. Tried editing as suggested too.. doesn't work... Kindly suggest some solution..