  As the most critical components in a sentence, subject, predicate and object
require special attention in the video captioning task. To implement this idea,
we design a novel framework, named COllaborative three-Stream Transformers
(COST), to model the three parts separately and complement each other for
better representation. Specifically, COST is formed by three branches of
transformers to exploit the visual-linguistic interactions of different
granularities in spatial-temporal domain between videos and text, detected
objects and text, and actions and text. Meanwhile, we propose a
cross-granularity attention module to align the interactions modeled by the
three branches of transformers, then the three branches of transformers can
support each other to exploit the most discriminative semantic information of
different granularities for accurate predictions of captions. The whole model
is trained in an end-to-end fashion. Extensive experiments conducted on three
large-scale challenging datasets, i.e., YouCookII, ActivityNet Captions and
MSVD, demonstrate that the proposed method performs favorably against the
state-of-the-art methods.
