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Change Video Aspect Ratio

Turn a vertical clip into 16:9, a landscape video into 9:16 or 1:1 — stretch, letterbox, blur-fill or crop, free and private

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100% private. Your file is processed locally in your browser with WebAssembly — it is never uploaded to a server, stored, or seen by anyone.

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Change Video Aspect Ratio converts any clip to a new frame shape — 16:9 for YouTube and TV, 9:16 for Shorts, Reels and TikTok, 1:1 or 4:5 for Instagram, 4:3 or 21:9. You choose how the picture should fit the new frame: stretch it to fill (fast, but it distorts), add black bars (letterbox or pillarbox, nothing is lost), place it over a blurred copy of itself (the popular "blurred background" look), or crop to fill so the frame is full and only the edges are cut off.

Everything runs locally in your browser with ffmpeg.wasm, a WebAssembly build of FFmpeg, using its scale, pad, boxblur, overlay and crop filters. Your video is never uploaded, there is no signup and no watermark. The output keeps the longer side of your source resolution (a 1080×1920 vertical clip becomes 1920×1080 in 16:9), re-encodes the picture once with H.264 at high quality and copies the audio track untouched.

Why use this tool

Four ways to fit the frame

Stretch, black bars, blurred background or crop — pick the look each platform expects instead of being stuck with one method.

Ready-made platform ratios

16:9 for YouTube, 9:16 for Shorts, Reels and TikTok, 1:1 and 4:5 for Instagram, 4:3 and 21:9 for everything else.

Private, in-browser processing

ffmpeg.wasm renders the video on your own device; nothing is uploaded, stored or watermarked.

Sensible output size

The longer side of your source resolution is preserved, so a Full HD clip stays Full HD in its new shape.

How to use the Change Video Aspect Ratio

Upload your video
Drag and drop the clip or click to choose it — it opens directly in the browser and is never uploaded.
Pick the target aspect ratio
Choose 16:9, 9:16, 1:1, 4:5, 4:3 or 21:9 depending on where the video will be published.
Choose how to fit the picture
Black bars or Blurred background keep the whole picture, Crop fills the frame by trimming the edges, Stretch fills it by distorting.
Convert and download
Click Change Aspect Ratio, wait for the local ffmpeg.wasm render and download the finished MP4.

Popular use cases

Publishing a phone-shot vertical clip on YouTube or a TV screen as 16:9 with a blurred background.
Cutting a landscape gameplay or interview recording into a 9:16 vertical for TikTok, Reels or Shorts.
Making a 1:1 or 4:5 version of a product video for an Instagram feed post.
Stretching an old 4:3 recording to 16:9 so it fills a modern widescreen display.

Frequently asked questions

Is the aspect ratio changer free?

Yes. It is completely free, with no account, no watermark and no limit on the number of videos. Processing happens on your device, so there is nothing to pay for on our side.

Is my video uploaded anywhere?

No. The conversion runs entirely in your browser via ffmpeg.wasm (WebAssembly). The file never leaves your computer or phone, which makes the tool safe for private footage.

What is the difference between stretch, black bars, blurred background and crop?

Stretch resizes the picture to the new frame ignoring proportions, so people and objects look wider or taller. Black bars scale the picture to fit and fill the rest with black — nothing is distorted or lost. Blurred background does the same but fills the bars with a blurred, enlarged copy of the frame, which looks natural on social apps. Crop scales the picture to fill the whole frame and cuts off whatever sticks out at the edges.

How do I make a vertical (9:16) video 16:9 for YouTube?

Pick 16:9 as the target and choose Blurred background or Black bars. Your vertical clip is placed in the centre of a 1920×1080 frame; with the blurred option the sides show a soft, enlarged copy of the video instead of black. Use Stretch only if you deliberately want the wide-screen "stretched" look.

How do I turn a landscape video into 9:16 for TikTok, Reels or Shorts?

Choose 9:16 and Crop to fill if the subject is in the centre — the frame is filled and the left/right edges are removed. If you need to keep the whole picture, choose Blurred background: the clip sits in the middle of a 1080×1920 frame over a blurred version of itself.

What resolution does the output have?

The longer side of your source is kept and the other side is derived from the target ratio. A 1920×1080 clip converted to 9:16 becomes 1080×1920; converted to 1:1 it becomes 1920×1920 (or 1080×1080 in crop mode, which never upscales). Dimensions are rounded to even numbers for H.264.

Does changing the aspect ratio reduce quality?

The picture is re-encoded once with H.264 at CRF 20, which is visually close to the original at normal bitrates. Stretch and blur-fill involve scaling, so extreme changes can soften the image slightly; black bars and crop keep the original pixels inside the frame. Audio is copied without re-encoding.

Which formats are supported and what do I get back?

You can load MP4, MOV, MKV, WebM, AVI, M4V, FLV, WMV, MPG or 3GP. The result is always an MP4 (H.264 + original audio) with the fast-start flag, ready for YouTube, Instagram, TikTok, Telegram or WhatsApp.

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