To resize a video with FFmpeg without distorting it, set one dimension and let FFmpeg compute the other: -vf scale=-2:720 gives you a 720-pixel-tall video whose width follows the source aspect ratio, rounded to an even number. If you need an exact frame size such as 1280x720, scale into that box with force_original_aspect_ratio=decrease and pad the rest, or scale over it with increase and crop . Never type both numbers on their own: scale=1280:720 on a portrait clip stretches it.

Everything below was run on November 13, 2026 with Homebrew FFmpeg 9.0.1 on macOS against one real 10-second clip: a 540x960, 24 fps, H.264 + AAC duet video (the portrait example from Voor's Alors on Danse AI page, md5 b839832a86193c30410ae39d8855a8ae , public at https://cdn.voor.ai/voor/keyword-landing/alors-on-danse-ai/v20261016/duet-9x16-source-v3.mp4 ).…