  Masked visual modeling (MVM) has been recently proven effective for visual
pre-training. While similar reconstructive objectives on video inputs (e.g.,
masked frame modeling) have been explored in video-language (VidL)
pre-training, previous studies fail to find a truly effective MVM strategy that
can largely benefit the downstream performance. In this work, we systematically
examine the potential of MVM in the context of VidL learning. Specifically, we
base our study on a fully end-to-end VIdeO-LanguagE Transformer (VIOLET), where
the supervision from MVM training can be backpropagated to the video pixel
space. In total, eight different reconstructive targets of MVM are explored,
from low-level pixel values and oriented gradients to high-level depth maps,
optical flow, discrete visual tokens, and latent visual features. We conduct
comprehensive experiments and provide insights into the factors leading to
effective MVM training, resulting in an enhanced model VIOLETv2. Empirically,
we show VIOLETv2 pre-trained with MVM objective achieves notable improvements
on 13 VidL benchmarks, ranging from video question answering, video captioning,
to text-to-video retrieval.
