Soft　computing　is　facing　a　rapid　evolution　thanks　to　the　development　of　artificial　intelligence　especially　the　deep　learning.　With　video　surveillance　technologies　of　soft　computing,　such　as　image　processing,　computer　vision,　and　pattern　recognition　combined　with　cloud　computing,　the　construction　of　smart　cities　could　be　maintained　and　greatly　enhanced.　In　this　article,　we　focus　on　the　online　detection　of　action　start　task　in　video　understanding　and　analysis,　which　is　critical　to　the　multimedia　security　in　smart　cities.　We　propose　a　novel　model　to　tackle　this　problem　and　achieves　state-of-the-art　results　on　the　benchmark　THUMOS14　data　set.　©　2005-2012　IEEE.