Why this resize-video tool is fast on Clipy
Resizing is scale + crop + re-encode, and the H.264 re-encode is the part that dominates wall-clock time. Browser-wasm ffmpeg runs it in a single CPU thread inside a tab, which is why competing free tools take minutes for any clip over a few seconds. We run native ffmpeg on dedicated workers — the encoder uses every available core, the wasm memory ceiling doesn't exist, and the upload + download legs ride your nearest Backblaze B2 POP via presigned URL. Closest edge in, Bunny CDN out, native encoder in the middle.
What this tool does, exactly
Each preset picks a target frame and the right scale/crop policy. YouTube (16:9 → 1920×1080) letterboxes a vertical source so faces don't get cropped — desktop viewers tolerate bars better than chopped subjects. TikTok / Reels / Shorts (9:16 → 1080×1920) and Instagram Square (1:1 → 1080×1080) scale-and-crop to fill the new frame, because bars on a vertical feed kill engagement. Instagram Portrait (4:5 → 1080×1350) is the highest-engagement ratio in the IG feed. Custom lets you set any exact width × height. Output is always H.264 (CRF 22, visually transparent) + AAC (160 kbps) inside MP4 with +faststart and yuv420p pixel format — the combination every social platform autoplays without re-transcoding.
Why aspect ratio matters more than resolution
People obsess over 1080p vs 4K. Almost no one notices the difference on a phone. What viewers notice instantly is a 16:9 video shoved into a TikTok feed with thick black bars top and bottom, or a 9:16 phone clip uploaded to YouTube as a tiny strip in the middle of a desktop screen. Resolution is invisible; aspect ratio is the first thing the eye sees. Get this right and the clip stops looking like it came from somewhere else. The four ratios that cover 99% of social: 16:9 (YouTube, LinkedIn, X, Vimeo, web embeds), 9:16 (TikTok, Instagram Reels, YouTube Shorts, Snapchat), 1:1 (Instagram feed, Facebook feed), and 4:5 (Instagram portrait — the highest-engagement IG feed shape).
Sister tools
For pure aspect-ratio presets without dimension tuning, use aspect ratio converter. To cut a specific region out of the frame first, crop video. Fixing orientation before resizing? Rotate video. After resizing, run output through video compressor if file size is still a problem, or mute video for autoplay-muted social embeds. Stitching several resized clips into one feed post? Merge videos.
Record straight to the right size
Resizing is always a compromise — either you throw away pixels (crop-to-fill) or you add empty bars (letterbox). If you're recording the source yourself, record with Clipy and pick the aspect ratio at capture time so you never have to come back here.