Dynamic transcoding can be used to provide supplemental content, selected to be played during breaks in a stream of primary content, that has the same format as the primary content. It can be desirable to provide supplemental content that is personalized. This may include additional content or advertising that may be of interest or relevance to a viewer. In many instances, the supplemental content will come from a different source and thus can be in a different format. Approaches in accordance with various embodiments can take advantage of dynamic transcoding of the supplemental content to provide properly formatted supplemental content through the same stream as the primary content. A custom manifest can be provided to the media player that points to the transcoded supplemental content. At an appropriate break in the playback, the media player can use the manifest to obtain the formatted supplemental content.