Techniques are described for providing media presentations that include content originating from multiple sources in ways that are effectively transparent to end user devices. Manifest data provided to an end user device include a key encoded in the URL for each of the content fragments. The key encodes one or more interstitial periods of secondary content within the overall presentation of primary content. When a media server receives a content request from the end user device, the media server determines from the key encoded in the URL and the range of content requested whether the request corresponds to the primary content or the secondary content.