  The watch time is a significant indicator of user satisfaction in video
recommender systems. However, the prediction of watch time as a target variable
is often hindered by its highly imbalanced distribution with a scarcity of
observations for larger target values and over-populated samples for small
values. State-of-the-art watch time prediction models discretize the continuous
watch time into a set of buckets in order to consider the distribution of watch
time. However, it is highly uninvestigated how these discrete buckets should be
created from the continuous watch time distribution, and existing
discretization approaches suffer from either a large learning error or a large
restoration error. To address this challenge, we propose a
Classification-Restoration framework with Error-Adaptive-Discretization (CREAD)
to accurately predict the watch time. The proposed framework contains a
discretization module, a classification module, and a restoration module. It
predicts the watch time through multiple classification problems. The
discretization process is a key contribution of the CREAD framework. We
theoretically analyze the impacts of the discretization on the learning error
and the restoration error, and then propose the error-adaptive discretization
(EAD) technique to better balance the two errors, which achieves better
performance over traditional discretization approaches. We conduct detailed
offline evaluations on a public dataset and an industrial dataset, both showing
performance gains through the proposed approach. Moreover, We have fully
launched our framework to Kwai App, an online video platform, which resulted in
a significant increase in users' video watch time by 0.29% through A/B testing.
These results highlight the effectiveness of the CREAD framework in watch time
prediction in video recommender systems.
