Reframe 16:9 to 9:16 before you burn captions, not after

Reframe before captions. A 9:16 window of a 16:9 frame is 81/256 = 0.3164 of the width at full height, centered at x = 0.3418, and captions burned onto the 16:9 file would be cropped away or sit off the safe area, so crop first and caption the vertical file. Trim, crop and caption cost $0.02 + $0.02 + $0.20 = $0.24 for a clip up to 60 seconds.

YouTube says Shorts are vertical videos up to 3 minutes with a 1080p maximum upload resolution (read 2026-10-09), so a 1080-high crop of a 1080p source is the right size.

The crop fractions

Video filter crops by fractions of the frame, so you do not need pixels. For source width W and height H, the 9:16 window has height 1 and width = (9/16) x H / W. For 1920 x 1080 that is 0.3164 (607.5 px of 1920), and x = (1 - width) / 2 = 0.3418. The compiler rounds to even pixel values for yuv420p.

{
  "video_url": "https://media.sume.com/artifacts/artf_demo/talk-169.mp4",
  "ops": [{ "op": "crop", "x": 0.3418, "y": 0, "width": 0.3164, "height": 1 }]
}

Order and cost

Gotchas

• A center crop is a guess about where the speaker stands; extract one still with video frames before you commit.
• /v1/video-filter/check is free and reports diagnostics instead of a 400, so run it first.
• Out-of-range fractions fail with video_filter_crop_out_of_bounds; a side under 0.05 also fails.
• The filter source must be 300 s or shorter.