the variable depthMov
is a structural array, the video data for each frame is the field cdata
.
for your application it look like you need to make sure the data in depthMov.cdata
is uint8.
in your code you can do this as you assign each frame to depthMov.cdata
in the for loop.
try this
for k = 1:dFrames
depthMov(k).cdata=uint8(read(depthPlayback,k));
end
NB the line above this in your code has, what i presume, is a typo and should be
depthMov(1:dFrames)=struct('cdata',zeros(dHeight,dWidth,3,'unit8'),'colormap',[]);
see here for more on matlab fundamentals including different data types.