In one aspect, a method includes transmitting a request for supplemental content for use by a content-presentation device that is scheduled to perform a content-modification operation at a start-time and, in response to the request: receiving, into a first buffer of the content-presentation device, first supplemental content having a first video quality that is higher than or equal to a predefined threshold, and receiving, into a second, different buffer of the content-presentation device, second supplemental content having a second video quality lower than the predefined threshold. The method also includes within a predefined time period before the start-time, determining whether an entirety of the first supplemental content has been received into the first buffer. The method also includes based on the determination, selecting supplemental content from a set of supplemental content that includes the first and second supplemental content, and performing the content-modification operation using the selected supplemental content.