YouTube channelBanners.insert: 6 MB JPEG or PNG limit for AI banners

YouTube's channelBanners.insert takes a JPEG or PNG up to 6,291,456 bytes (6 MiB). That is the tightest image cap among the channel-art endpoints in the discovery document, tighter than the 10 MiB for watermarks and the 50 MiB for playlist images. For an AI banner, choose JPEG and check the file size before uploading.

How do the three image caps compare?

The document lists each cap in the upload settings of its method. All three accept image/jpeg and image/png.

How do I make a banner within the cap?

Banner art is wide, so use a wide aspect_ratio such as 16:9 or 21:9, both on the Sume list, and request jpeg. A photograph-like banner as JPEG is much smaller than the same image as PNG, though Sume does not promise a byte size. Measure the result and re-request at a different tier if it is over.

import json, os, urllib.request

body = {
    "model": "bytedance-seed/seedream-4.5",
    "prompt": "wide banner, soft gradient sky over a quiet harbor, lots of empty space on the sides",
    "aspect_ratio": "21:9",
    "output_format": "jpeg"
}
req = urllib.request.Request(
    "https://api.sume.com/v1/images",
    data=json.dumps(body).encode(),
    headers={
        "Authorization": "Bearer " + os.environ["SUME_API_KEY"],
        "Content-Type": "application/json",
    },
    method="POST",
)
print(urllib.request.urlopen(req).read().decode())

Which pixel size does YouTube want?

The discovery document does not state pixel dimensions. Use YouTube's help guidance for the banner size and safe area, then compare it with what Sume returns. Keep key content centered.

What should I verify?

Test with a channel you control. The images guide covers the parameters, and the related banner guide covers layout.