YouTube thumbnails take JPG or PNG: output formats per Sume image row

YouTube's thumbnail help page lists JPG and PNG as acceptable formats, so a WebP file is not what you upload. On Sume, most image rows list png, jpeg and webp and take output_format, Recraft V4 lists only webp, and Higgsfield Soul and Ideogram 4.5 list none because the provider picks the format. Convert those outputs before upload.

Formats per row

YouTube's side

YouTube also asks for a 16:9 aspect ratio on video thumbnails, 9:16 for Shorts, and 1:1 for podcast playlists. Mobile uploads are limited to 2 MB and desktop to 50 MB for videos and Shorts (YouTube Help, read 2026-10-07). The page also says vertical videos with a 16:9 custom thumbnail get an auto-generated 4:5 thumbnail on home, explore and subscription pages.

Convert WebP to JPG

If a row gives you WebP, convert it. This Pillow snippet reads a downloaded file and writes a JPEG, flattening any transparency on white:

from PIL import Image

src = Image.open("thumb.webp")
if src.mode in ("RGBA", "LA"):
    flat = Image.new("RGB", src.size, "white")
    flat.paste(src, mask=src.getchannel("A"))
    src = flat
src.convert("RGB").save("thumb.jpg", "JPEG", quality=90)

Choosing

• For direct upload, pick a row that takes output_format: "png" or "jpeg" and ask for it.
• Keep the file under 2 MB if you upload from a phone; JPEG is smaller than PNG for photographic art.
• Use aspect_ratio: "16:9" for videos and 9:16 for Shorts; every row lists both.
• Transparent backgrounds need PNG or WebP and ChatGPT Image 2.5, which is not what a thumbnail needs.

File size in practice

YouTube lists 2 MB on mobile and 50 MB on desktop. A PNG of a detailed image can be large, so check the file size after conversion and keep a smaller JPG for phone uploads.

Do not resize on upload. Ask for the right ratio at generation time (16:9 for videos, 9:16 for Shorts), keep the long edge reasonable for the row, and convert once.

Reference

Row capabilities come from GET /v1/images/models, described on the Image API page. If a field is not listed for a row, Sume answers 400 unsupported_parameter instead of dropping it.