Crop a 16:9 video to a centered 9:16 strip: the crop fractions

Sume's crop op takes fractions of the source frame, not pixels. For a centered 9:16 strip from a 16:9 video, the fractions are x 0.3418, y 0, width 0.3164, height 1, because 9/16 divided by 16/9 is 81/256, or 0.3164, and half of what is left is 0.3418. The same arithmetic gives 1:1 and 4:5 in the table. This works for any 16:9 source, whatever its pixel size.

The crop rules are from the video filter docs, read 2026-10-02; the arithmetic is mine and you can check it against any frame size.

What are the crop rules?

Per the docs, x and y are in 0 to 1, width and height in 0.05 to 1, x + width and y + height must not exceed 1, and the compiler rounds to even sizes for yuv420p. A fraction that misses the frame, or a side under 0.05, is video_filter_crop_out_of_bounds. A crop op carries only op, x, y, width, height; any extra key is unsupported_filter_op_field.

curl -X POST https://api.sume.com/v1/video-filter \
  -H "Authorization: Bearer $SUME_API_KEY" \
  -H "Content-Type: application/json" \
  -H "Idempotency-Key: center-9x16-001" \
  -d '{
    "video_url": "https://media.sume.com/artifacts/artf_demo/wide.mp4",
    "ops": [{ "op": "crop", "x": 0.3418, "y": 0, "width": 0.3164, "height": 1 }]
  }'

What does a crop to 16:9 source give for other ratios?

For a 16:9 source, a full-height centered crop to ratio r has width (r) divided by (16/9) and x of half the remainder.

Does the crop make a 1080x1920 file?

No. A crop returns the cropped pixels at their own size: a 1920x1080 source cropped to 0.3164 wide is about 608x1080. To reach 1080x1920, chain a scale filter in filtergraph (it runs after ops[]), or build the shot in Timeline 1.0 with output width and height and fit: "cover". Scaling a narrow crop up makes it softer, so crop from the highest-resolution source you have.