Trimplayer PortCast defines an open JSON-based interchange format, and an optional HTTPS synchronisation API, for moving a podcast listener's data -- subscriptions, listening history, playback position, queue, bookmarks, and per-feed preferences -- between independent podcast applications without a central service. It builds on identifiers already present in RSS (item GUID, feed URL) and the Podcast Namespace (podcast:guid) so that implementations can interoperate without inventing a new identity namespace. This document specifies the file format (v0.1) and a federated synchronisation API (v0.2) that reuses the same data model.