Systems and methods for identifying, assembling, and publishing content are described. A content item, such as a video, having a first time length, is identified by a system to be included in a program scheduled for a first time period. The video may be hosted on a third party system. A first span of time within the first program is allocated for the video, wherein the first span of time is longer than the first time length. The system determines, prior to or at the first time period, a time difference between a current length of the video and the first span of time. At least partly in response to determining that the video has a time length shorter than the first span of time, the system selects supplemental content based at least in part of the determined time difference to be streamed to user terminals over a data network within the first time period.