  Large scale Vision-Language (VL) models have shown tremendous success in
aligning representations between visual and text modalities. This enables
remarkable progress in zero-shot recognition, image generation & editing, and
many other exciting tasks. However, VL models tend to over-represent objects
while paying much less attention to verbs, and require additional tuning on
video data for best zero-shot action recognition performance. While previous
work relied on large-scale, fully-annotated data, in this work we propose an
unsupervised approach. We adapt a VL model for zero-shot and few-shot action
recognition using a collection of unlabeled videos and an unpaired action
dictionary. Based on that, we leverage Large Language Models and VL models to
build a text bag for each unlabeled video via matching, text expansion and
captioning. We use those bags in a Multiple Instance Learning setup to adapt an
image-text backbone to video data. Although finetuned on unlabeled video data,
our resulting models demonstrate high transferability to numerous unseen
zero-shot downstream tasks, improving the base VL model performance by up to
14\%, and even comparing favorably to fully-supervised baselines in both
zero-shot and few-shot video recognition transfer. The code will be released
later at \url{https://github.com/wlin-at/MAXI}.
