Thumbnails

Introduction

When sending media, it is often helpful for users when a thumbnail can be shown before the actual file is finished downloading.

XMPP already has a protocol for specifying thumbails, Jingle Content Thumbnails. However, this protocol requires that the thumbnail is a base64-encoded image published using Bits of Binary. This prevents clients from implementing newer technologies, such as Blurhash.

This document specifies are more general and extensible element for specifiying thumbnails.

Usage

<thumbnail type="blurhash" xmlns="urn:xmpp:thumbnail:0">
	<payload>LEHV6nWB2yk8pyoJadR*.7kCMdnj</payload>
</thumbnail>

In this example, the thumbnail is specified of type blurhash, which means that a supporting client should decode the <payload/> element using the Blurhash algorithm.

In order to enable a sort-of interoperability with Jingle Content Thumbnails, a type urn:xmpp:thumbs:0 is defined. If this is specified, then a supporting client must interpret the child of the <payload /> as an <thumbnail /> element as specified by :Jingle Content Thumbnails

<thumbnail type="urn:xmpp:thumbs:1" xmlns="urn:xmpp:thumbnail:0">
	<payload>
		<thumbnail xmlns="urn:xmpp:thumbs:1" uri="..." media-type="image/png" width="128" height="96" />
	</payload>
</thumbnail>

In the case of Jingle Content Thumbnails compatibility, the <payload /> element must contain exactly one <thumbnail xmlns="urn:xmpp:thumbs:1" /> element.

Other extensions may define similar types. Note that the content of the <payload /> element is dependent on the type specified in the <thumbnail xmlns="urn:xmpp:thumbnail:0" /> element.

Thumbnail Types

Blurhash

If a sender specifies the type to be of blurhash, then the payload must contain the image data as specified by the Blurhash algorithm. Care should be taken to prevent the blurhash data from growing to large in order to prevent hitting the stanza size limit.

NOTE: This example is taken from Stateless Inline Media Sharing and modified for this protocol.

<message to='julient@shakespeare.lit' from='romeo@montague.lit'>
  <body>Look at the nice view from the summit.</body>
  <reference xmlns='urn:xmpp:reference:0' begin='17' end='20' type='data'>
    <media-sharing xmlns='urn:xmpp:sims:1'>
      <file xmlns='urn:xmpp:jingle:apps:file-transfer:5'>
        <media-type>image/jpeg</media-type>
        <name>summit.jpg</name>
        <size>3032449</size>
        <hash xmlns='urn:xmpp:hashes:2' algo='sha3-256'>2XarmwTlNxDAMkvymloX3S5+VbylNrJt/l5QyPa+YoU=</hash>
        <hash xmlns='urn:xmpp:hashes:2' algo='id-blake2b256'>2AfMGH8O7UNPTvUVAM9aK13mpCY=</hash>
        <desc>Photo from the summit.</desc>
        <thumbnail type="urn:xmpp:thumbs:1" xmlns='urn:xmpp:thumbnail:0'>
		  	<payload>
				<thumbnail xmlns='urn:xmpp:thumbs:1'uri='cid:sha1+ffd7c8d28e9c5e82afea41f97108c6b4@bob.xmpp.org' media-type='image/png' width='128' height='96'/>
			</payload>
		</thumbnail>
        <thumbnail type="blurhash" xmlns='urn:xmpp:thumbnail:0'>
		  	<payload>LEHV6nWB2yk8pyoJadR*.7kCMdnj</payload>
		</thumbnail>
      </file>
      <sources>
        <reference xmlns='urn:xmpp:reference:0' type='data' uri='https://download.montague.lit/4a771ac1-f0b2-4a4a-9700-f2a26fa2bb67/summit.jpg' />
        <reference xmlns='urn:xmpp:reference:0' type='data' uri='xmpp:romeo@montague.lit/resource?jingle;id=9559976B-3FBF-4E7E-B457-2DAA225972BB' />
      </sources>
    </media-sharing>
  </reference>
</message>

Security Considerations

The same considerations apply as specified by Jingle Content Thumbnails.

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