joystream/content-metadata-protobuf/doc-appendix.md

Referencing Assets

Applications that process messages that contain a uint32 field that references an asset such as a cover photo or video, should interpret this value as a zero based index into an array/vector that is received external (out of band) to the protobuf message.

Example in context of query-node processing the runtime event VideoCreated

// Runtime event associated with creating a Video
VideoCreated(video_id: VideoId, video: Video, assets: Vec<NewAsset>, params: VideoCreationParameters)

struct VideoCreationParameters {
  in_category: VideoCategoryId,
  // binary serialized VideoMetadata protobuf message
  meta: Vec<u8>,
}

// suppose assets is a vector of two elements. This is the "out of band" array being referenced by the VideoMetadata message
assets = [
    NewAsset::Uri("https://mydomain.net/thumbnail.png"),
    NewAsset::Upload({
       content_id,
       ipfs_hash,
       size,
       ...
    }),
];

meta = VideoMetadata {
    ...
    // refers to second element: assets[1] which is being uploaded to the storage system
    video: 1,
    // refers to the first element assets[0] which is being referneced by a url string.
    thumbnail_photo: 0,
    ...
};