Black bars on a YouTube Short: YouTube says no, so fill the frame

Don't leave black bars in the file. YouTube's formatting page says videos should be in their native aspect ratios and that uploaded videos should never include letterboxing or pillarboxing bars; the player automatically frames a video so it is displayed without cropping or stretching. For a Short, YouTube's upload page asks for a file up to 3 minutes with a square or vertical aspect ratio.

So a 16:9 clip dropped into a 9:16 frame with bars above and below breaks both rules. Sume's Timeline has four fit modes, and one fills the bars without distortion.

What does YouTube say about aspect ratio?

The formatting page says frame the picture at its native shape. If the native ratio is 1.77:1 and the frame is also 1.77:1, use 16:9 with square pixels and no border. If the frame is not that shape, it says to use 16:9 matting with square pixels and a single-color border that doesn't vary over time. The same rule exists for 1.33:1 and 4:3.

Read that as guidance for ordinary uploads. For Shorts, the upload page is the one to follow: up to 3 minutes, square or vertical. You can also select up to 15 short videos at a time, then use Edit draft to complete each one's details before publishing.

Which Sume fit mode fills the frame?

Timeline 1.0 takes a fit on each video[] slot, and the default output is 1080 by 1920. The doc lists four values. Their effects below are described from the option names, so try each on a short test render.

When should I crop instead?

If the subject is in the middle of the frame, cover is usually enough. If the clip has text at the edges, a crop cuts it off, so use blur or reshoot. You can also change pixels before assembly with video filter, which supports crop ops, then place the result in a timeline.

One caution: a blurred fill is not a licence to keep a small picture in a big frame. A thin 16:9 strip in the middle of a tall frame still reads as a letterbox to many viewers, so prefer cover when you can.

Example request

This renders one 16:9 clip into a 1080 by 1920 frame with a blurred fill. Import the clip first, since Timeline only reads your workspace's media.sume.com files; the media inputs page shows how. Run /v1/timeline-1.0/plan first if you want the free preflight.

curl -X POST https://api.sume.com/v1/timeline-1.0/render \
  -H "Authorization: Bearer $SUME_API_KEY" \
  -H "Content-Type: application/json" \
  -H "Idempotency-Key: blur-fill-001" \
  -d '{
    "audio": {"url": "https://media.sume.com/artifacts/artf_demo/talk.wav", "duration_seconds": 20},
    "video": [
      {"source_url": "https://media.sume.com/artifacts/artf_demo/talk.mp4",
       "start": 0, "duration": 20, "fit": "blur"}
    ],
    "output": {"width": 1080, "height": 1920}
  }'

What to check after the render

Open the result and look at the top and bottom edges. Then check that the length is within 3 minutes, because YouTube's Shorts rule is a length and a shape, and a clean frame does not help if the file is too long.