Guide

YouTube thumbnail glossary

The words this desk uses on purpose, so a search snippet and a human mean the same file. Filenames are not marketing. They are paths on i.ytimg.com.

Last reviewed August 2026. Pair with the size chart when you need pixels.

maxresdefault

The HD JPEG at /vi/{id}/maxresdefault.jpg, typically 1280×720 when a custom 16:9 thumb exists. Often missing. Not 4K.

hq720

Another 1280×720 JPEG YouTube serves on many videos when maxres is absent.

sddefault / hqdefault / mqdefault / default

Smaller JPEGs: 640×480, 480×360, 320×180, 120×90. HQ is the reliable fallback. SD is 4:3 and often letterboxed. default.jpg is supposed to be 120×90; maxres at that size is a placeholder.

0.jpg – 3.jpg

Auto-generated frames YouTube picked from the video. See custom vs auto.

vi / vi_webp

CDN directories for JPEG and WebP stills with the same ID. Example: https://i.ytimg.com/vi_webp/VIDEO_ID/hqdefault.webp.

i.ytimg.com / img.youtube.com

Image hosts for public stills. Same /vi/{id}/ objects in most cases. The watch host www.youtube.com is not the image host. Details: URL format.

Placeholder

A 120×90 (or similarly tiny) image returned instead of a 404 when maxres does not exist. Not HD.

Video ID

Eleven characters identifying the video. Not a channel ID or playlist ID. How to find it.

Channel ID / playlist ID

Channel IDs start with UC and are longer than 11 characters. Playlist IDs often start with PL, UU, or LL. Neither one is a thumbnail key until you have a video ID.

oEmbed

YouTube’s public JSON for title, author, and a thumbnail URL on many public videos. No API key on this site. Endpoint: https://www.youtube.com/oembed?format=json&url=….

Safe zone

The region of a still that remains readable after titles, duration badges, and mobile gradients. Guide.

UHD / 4K thumbnail

Marketing language. Public stills are almost never 3840×2160. Reality.

si= / feature=

Share and UI query flags on watch URLs. They do not change the still. Strip them with the link cleaner.

Custom thumbnail

The 16:9 image you upload in Studio (JPEG, PNG, or GIF, under 2 MB). When YouTube publishes HD, it is usually what maxresdefault becomes.

YouTube thumbnail terms FAQ

What does maxresdefault mean?

The HD JPEG at i.ytimg.com/vi/{id}/maxresdefault.jpg, typically 1280x720 when a custom 16:9 thumb exists. Often missing. Not 4K.

What is hqdefault on YouTube?

hqdefault.jpg is a 480x360 (4:3) still that almost always exists. A 16:9 custom thumb is letterboxed inside it.

What is a YouTube video ID?

Eleven characters that identify the video. Thumbnail CDN paths key off this ID, not the title.

What is a YouTube thumbnail placeholder?

A tiny 120x90 image (often a broken-film graphic) returned at a maxres URL when HD was never published. HTTP 200 does not mean HD.

What is oEmbed for YouTube?

A public JSON endpoint that returns title, author, and a thumbnail URL for many public videos. No API key. Unlisted and private often fail.

What is vi_webp?

The CDN directory for WebP stills: i.ytimg.com/vi_webp/{id}/maxresdefault.webp. Same pixels as the JPEG twin, not a resolution upgrade.