  The last several years have witnessed remarkable progress in
video-and-language (VidL) understanding. However, most modern VidL approaches
use complex and specialized model architectures and sophisticated pretraining
protocols, making the reproducibility, analysis and comparisons of these
frameworks difficult. Hence, instead of proposing yet another new VidL model,
this paper conducts a thorough empirical study demystifying the most important
factors in the VidL model design. Among the factors that we investigate are (i)
the spatiotemporal architecture design, (ii) the multimodal fusion schemes,
(iii) the pretraining objectives, (iv) the choice of pretraining data, (v)
pretraining and finetuning protocols, and (vi) dataset and model scaling. Our
empirical study reveals that the most important design factors include:
temporal modeling, video-to-text multimodal fusion, masked modeling objectives,
and joint training on images and videos. Using these empirical insights, we
then develop a step-by-step recipe, dubbed VindLU, for effective VidL
pretraining. Our final model trained using our recipe achieves comparable or
better than state-of-the-art results on several VidL tasks without relying on
external CLIP pretraining. In particular, on the text-to-video retrieval task,
our approach obtains 61.2% on DiDeMo, and 55.0% on ActivityNet, outperforming
current SOTA by 7.8% and 6.1% respectively. Furthermore, our model also obtains
state-of-the-art video question-answering results on ActivityNet-QA, MSRVTT-QA,
MSRVTT-MC and TVQA. Our code and pretrained models are publicly available at:
https://github.com/klauscc/VindLU.
