  Video transformer naturally incurs a heavier computation burden than a static
vision transformer, as the former processes $T$ times longer sequence than the
latter under the current attention of quadratic complexity $(T^2N^2)$. The
existing works treat the temporal axis as a simple extension of spatial axes,
focusing on shortening the spatio-temporal sequence by either generic pooling
or local windowing without utilizing temporal redundancy.
  However, videos naturally contain redundant information between neighboring
frames; thereby, we could potentially suppress attention on visually similar
frames in a dilated manner. Based on this hypothesis, we propose the LAPS, a
long-term ``\textbf{\textit{Leap Attention}}'' (LA), short-term
``\textbf{\textit{Periodic Shift}}'' (\textit{P}-Shift) module for video
transformers, with $(2TN^2)$ complexity. Specifically, the ``LA'' groups
long-term frames into pairs, then refactors each discrete pair via attention.
The ``\textit{P}-Shift'' exchanges features between temporal neighbors to
confront the loss of short-term dynamics. By replacing a vanilla 2D attention
with the LAPS, we could adapt a static transformer into a video one, with zero
extra parameters and neglectable computation overhead ($\sim$2.6\%).
Experiments on the standard Kinetics-400 benchmark demonstrate that our LAPS
transformer could achieve competitive performances in terms of accuracy, FLOPs,
and Params among CNN and transformer SOTAs. We open-source our project in
\sloppy
\href{https://github.com/VideoNetworks/LAPS-transformer}{\textit{\color{magenta}{https://github.com/VideoNetworks/LAPS-transformer}}} .
