What is significant about all ABR formats is that they separate the control aspects of the protocol from the video data. They share the general concept that video data is encoded into chunks and placed onto an origin server or a CDN. To start a streaming session, client devices load a manifest file from that server that tells them what chunks to load and in what order. The infrastructure that serves the manifest can be completely separate from the infrastructure that serves the chunks.
The separation of these concerns provides a basis for dynamic content replacement, as it is possible to dynamically manipulate the manifest file to point the client device at an alternative sequence of video chunks that have been pre-encoded and placed on the CDN. The ability to swap chunks out in this way relies on the encoding workflow generating video chunks whose boundaries match possible replacement events.
Via Nicolas Weil