Change Aspect Ratio of Video

About Change Aspect Ratio

Cross-platform creators live this nightmare: shoot once in 16:9 horizontal, then need 9:16 for TikTok/Reels/Shorts, 1:1 for Instagram feed, 4:5 for the LinkedIn and Instagram portrait feed, 21:9 for cinematic teasers. Each platform re-transcodes and downrates videos that don't match its native aspect, hurting reach. This tool reshapes any video to a spec-correct delivery resolution using ffmpeg.wasm in your browser: pick 16:9 (1920x1080), 9:16 (1080x1920), 1:1 (1080x1080), 4:3 (1440x1080), 4:5 (1080x1350) or 21:9 (2560x1080) from the preset selector, or choose Custom W:H for any ratio. Crop fills the frame and discards edges (best when the subject is centered), Pad adds letterbox/pillarbox bars or a blurred background fill (preserves all content, ideal for landscape-to-portrait conversion of interview footage), or Stretch warps to fit (rarely correct, but useful for forced framing). MP4/MOV output is written with faststart so social players and progressive web previews start instantly. All processing happens client-side via WebAssembly — no upload, no watermark, no cloud quota. See also our Compress Video and Video to GIF.

What aspect ratios and output resolutions are supported?

Presets map to standard delivery sizes: 16:9 (1920x1080), 9:16 (1080x1920) for Reels/TikTok, 1:1 (1080x1080), 4:3 (1440x1080), 4:5 (1080x1350) for the Instagram/LinkedIn portrait feed, and 21:9 (2560x1080) ultrawide. Choose Custom W:H to enter any width:height ratio; for custom ratios the canvas is derived from your source's dominant dimension and rounded to even pixels so codecs accept it.

Why are the outputs web-ready (faststart)?

MP4 and MOV files normally place the moov atom (the index) at the end, so a web or social player must download the whole file before playback starts. This tool adds -movflags +faststart, moving the moov atom to the front so progressive streaming and previews begin immediately — important when delivering to Instagram, TikTok and YouTube.

Letterbox vs pillarbox — and how do I avoid cutting my subject?

Letterboxing adds bars top and bottom (a wide video placed in a taller/square frame); pillarboxing adds bars left and right (a tall or narrow video placed in a wider frame) — both use the Pad method. When converting landscape to vertical, Crop discards the sides, so keep your subject centered or use Pad with a blurred background to preserve the full frame and the social safe area.

What's the difference between Crop, Pad, and Stretch?

Crop: Fills the new frame by cutting edges (no distortion). Pad: Adds black bars to fit (keeps all content). Stretch: Distorts video to fit exactly (may look unnatural).

What are padding color options?

Black (classic letterbox/pillarbox), White (bright background), or Blurred (uses blurred video as background for aesthetic look).

How do the High/Medium/Low quality tiers map to bitrate and CRF?

Re-encoding is lossy, so the output is rebuilt from the source rather than copied. For MP4/MOV (H.264) the tiers set CRF: High = CRF 18 (near-visually-lossless, larger files, veryfast preset), Medium = CRF 23 (balanced default), Low = CRF 28 (smaller files, softer detail). Lower CRF means higher quality and bigger files. WebM output uses VP8 at roughly 2M / 1M / 500k target bitrate for High/Medium/Low. Output is encoded as yuv420p for maximum player and platform compatibility.

Which codecs and containers are supported?

MP4 and MOV are encoded with H.264 video + AAC audio (the universal social/web combo); WebM is encoded with VP8 video + Vorbis audio. Choose 'Same as Input' to keep the source container, or force MP4 for the broadest device support. WebM (VP8/VP9) is open and great for the web but not accepted everywhere, which is why H.264 MP4 is the default delivery format.

What is the file size limit?

Maximum file size is 100MB. This ensures smooth processing in your browser.

Can I preview before downloading?

Yes! After processing, you can preview the video with new aspect ratio before downloading.

Is my video file safe?

Absolutely! All processing happens in your browser using FFmpeg.wasm. Your video is never uploaded to any server.

How long does processing take?

Processing time depends on video length and settings. Typically 30-60 seconds for a 5-minute video.