fileDatastore read: Index exceeds the number of array elements (0).

I am attempting to set up a fileDatastore (vds, for video datastore) that will send 1 video file at a time to a modified version of the MotionBasedMultiObjectTrackingExamples.m. I have the following code:

loc = "C:\Users\Christine Deer\Downloads\02242021-SV\02242021-SV";
vds = fileDatastore(loc, 'ReadFcn', @videoReader, 'IncludeSubfolders', ...
    true, 'FileExtensions', '.mp4')

    data=read(vds);
function v = videoReader(file)
v = videoReader(file);
end

Which generates the following output:

vds = 

  FileDatastore with properties:

                       Files: {
                              ' ...\Camera 1 - 192.168.0.105 (FLIR A400) - 14-20210216-210329.mp4';
                              ' ...\Camera 1 - 192.168.0.105 (FLIR A400) - 14-20210218-012228.mp4';
                              ' ...\Camera 1 - 192.168.0.105 (FLIR A400) - 14-20210218-232125(1).mp4'
                               ... and 1 more
                              }
                     Folders: {
                              'C:\Users\Christine Deer\Downloads\02242021-SV\02242021-SV'
                              }
                 UniformRead: 0
                    ReadMode: 'file'
                   BlockSize: Inf
                  PreviewFcn: @videoReader
      SupportedOutputFormats: [1×16 string]
                     ReadFcn: @videoReader
    AlternateFileSystemRoots: {}

Error using matlab.io.datastore.FileDatastore/read (line 29)
Index exceeds the number of array elements (0).

Error in DatastoreLoad (line 5)
    data=read(vds);

This looks like vds is populated with the correct data. What I am confused by is that the data is in vds, but I cant seem to call the read properly to not get an error. Any help understanding this error and its resolution is greatly appreciated and thoroughly welcome,

Christine D

Answer 1

[Kojiro Saito]

videoReader function should be VideoReader.

Also, for avoiding function name conflict, it's better to use another name to custom function than videoReader.

vds = fileDatastore(loc, 'ReadFcn', @myVideoReader, 'IncludeSubfolders', ...
    true, 'FileExtensions', '.mp4')

function v = myVideoReader(file)
  v = VideoReader(file);
end

Or, simply, you don't need to use custom function in this case.

vds = fileDatastore(loc, 'ReadFcn', @VideoReader, 'IncludeSubfolders', ...
    true, 'FileExtensions', '.mp4')

[Christine Deer]

Thank you so much!