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It is typical for enterprises to rely on services from cloud providers in order to build a scalable platform with abundant available resources to satisfy user demand, and for cloud providers to deploy a number of datacenters inter-connected with high-capacity links, across different geographical regions. In this paper, we propose that video conferencing, even with its stringent delay constraints, should also be provided as a cloud service, taking full advantage of the inter-datacenter network in the cloud. We design Airlift, a new protocol designed for the inter-datacenter network, tailored to the needs of a cloud-based video conferencing service. Airlift delivers packets in live video conferences to their respective destination datacenters, with the objective of maximizing the total throughput across all conferences, yet without violating end-to-end delay constraints. In order to simplify our protocol design in Airlift, we use intra-session network coding and the concept of conceptual flows, such that the optimization problem that can be conveniently formulated as a linear program. Our real-world implementation of Airlift has been deployed over the Amazon EC2 cloud. We show that Airlift delivers a substantial performance advantage over state-of-the-art peer-to-peer solutions.