Editing Blob (section)

== Storage and Distribution ==
Blobs within the AT Protocol are uploaded alongside a [[record]]. For example, a user might publish a post with an attached image or video. Blobs follow a specific lifecycle:

# Users upload media to their [[Personal Data Server (PDS)]] using the <code>com.atproto.repo.uploadBlob</code> endpoint which returns verified metadata
# The uploaded blob is referenced in a record (such as a post)
# Once referenced, the blob becomes permanently stored until all references to the blob within the actor's [[data repository]] are deleted.

While stored on an actor's PDS, blobs are typically served to users via specialized protocol-independent [[wikipedia:Content_delivery_network|content delivery networks]]. This separation between storage and distribution allows applications to optimize media delivery, such as creating thumbnails or transcoding videos for different devices.

Each blob within a PDS includes a [[Content Identifier (CID)]], size information, and a [[wikipedia:Media_type|MIME type]] specification (e.g. <code>image/jpeg</code>, <code>video/mp4</code>). The CID ensures content identity, as any change to the blob would result in a different identifier, making it impossible to tamper with media content without detection.