A quick note on new operations in cv-calc utility. Time does not permit to present proper examples, but hopefully, cv-calc --help would be sufficient to give you an idea.
Output only those input images that conform a certain condition. Currently, only min/max number or ratio of non-zero pixels is supported, but the condition can be any set of filters applied to the input image (see cv-cat --help --verbose for the list of the filters available).
Example: Output only images that have at least 60% of pixels darker than a given threshold:
Stride to the input image with a given kernel (just like a convolution stride), output resulting images.
Thin the image stream by a given rate or a desired frames-per-second number.