Offer multiple audio format or bitrate downloads for a single podcast episode using the podcast:alternateEnclosure and podcast:source namespace tags

Steps

1. Within an episode's <item>, add one or more <podcast:alternateEnclosure> elements alongside the standard RSS <enclosure> to describe alternate or companion versions of the episode, such as a lower-bitrate file for constrained bandwidth, an audio-only track for a video episode, or an alternate codec
2. Nest one or more <podcast:source> child elements inside each alternateEnclosure to declare the actual URI(s) where that specific variant can be fetched, using the uri attribute to support alternate transport schemes (HTTP, IPFS, magnet/BitTorrent, Tor)
3. Set accurate type, length, and bitrate attributes on each alternateEnclosure so podcast apps that support the tag can present listeners with a meaningful choice
4. Use the isDefault attribute to indicate which alternateEnclosure, if any, should be preferred by supporting apps over the plain <enclosure>
5. Set contentType on a podcast:source only when that transport's file type differs from the underlying media's mime type (e.g., a .torrent file pointing at an MP3)
6. Validate the finished feed against a Podcast Index namespace validator before publishing, since malformed nesting is typically ignored silently rather than rejected