This patent document describes, among other things, distributed computer platforms for online delivery of multimedia, including HD video, at broadcast audience scale to a variety of runtime environments and client devices in both fixed line and mobile environments. The teachings hereof can be applied to deliver live and on-demand content streams via computer networks. The teachings also relate to the ingestion of content streams in a given source format and the serving of the stream in a given target format. For example, a system might have machines in a content delivery network that ingest live streams in a source format, use an intermediate format to transport the stream within the system, and output the stream in a target format to clients that have requested (e.g., with an HTTP request) the stream. The streams may be archived for later playback.