BYTETOOLS

Video Aspect Ratio Converter

Convert a video between 16:9, 9:16, 1:1 and 4:5 online free. Crop to fill or letterbox with a chosen color — right in your browser, never uploaded.

Drop a video here or click to browseYour video is processed locally and never uploaded.

What is the Video Aspect Ratio Converter?

The ByteTools Video Aspect Ratio Converter reshapes a clip for wherever it's going: 16:9 landscape for YouTube, 9:16 vertical for Reels, Shorts and TikTok, 1:1 square or 4:5 portrait for feeds, and classic 4:3.

  • Presets for 16:9, 9:16, 1:1, 4:5 and 4:3 at platform-standard sizes
  • Fit mode letterboxes with black, white or any custom color
  • Fill mode center-crops for a bar-free result
  • Ideal for turning landscape clips into vertical Reels/Shorts
  • 100% local processing — never uploaded
  • Free, watermark-free MP4 output

How to use the Video Aspect Ratio Converter

  1. 1

    Drop a video onto the box or click to browse for one.

  2. 2

    Choose the target format, e.g. 9:16 vertical for Reels and Shorts.

  3. 3

    Pick Fit (bars, keeps everything) or Fill (crops, no bars), and a bar color for Fit mode.

  4. 4

    Click Convert aspect ratio, preview and download the MP4.

About the Video Aspect Ratio Converter

The ByteTools Video Aspect Ratio Converter reshapes a clip for wherever it's going: 16:9 landscape for YouTube, 9:16 vertical for Reels, Shorts and TikTok, 1:1 square or 4:5 portrait for feeds, and classic 4:3. Pick the target, then choose how to get there.

Two honest modes cover every case. Fit keeps the entire frame and fills the leftover space with letterbox or pillarbox bars in a colour you choose; Fill crops the edges so the video covers the whole new frame with no bars. The most common job — making a horizontal video vertical — is two clicks.

The conversion runs 100% locally in your browser with a WebAssembly build of ffmpeg. Nothing is uploaded to any server, there are no accounts and no watermarks, and the output is a standard H.264 MP4 sized exactly for the platform you picked — 1080×1920 for vertical, 1920×1080 for widescreen, and so on.

Frequently asked questions

How do I make a horizontal video vertical for Reels or TikTok?

Choose the 9:16 vertical preset, then pick a mode: Fit keeps the whole clip with bars above and below, while Fill zooms and crops the sides so the frame is completely filled. For a nicer look than plain bars, the Blur Video tool offers a blurred-background vertical mode.

What is the difference between Fit and Fill?

Fit scales the video down until all of it is visible inside the new shape and pads the rest with a solid color — nothing is lost, but you get bars. Fill scales the video up until it covers the new shape and crops the overflow — no bars, but the edges are cut off.

Which aspect ratio should I use for each platform?

Use 16:9 for YouTube and presentations, 9:16 for Reels, Shorts, TikTok and Stories, 1:1 or 4:5 for Instagram and Facebook feed posts. The presets here output the standard pixel sizes each platform expects, like 1080×1920 for vertical.

Can I choose the color of the letterbox bars?

Yes. Fit mode offers black, white or any custom 6-digit hex color, so the bars can match your brand or blend with a page background. Invalid hex values safely fall back to black.

Is quality lost when changing the aspect ratio?

The clip is re-encoded at CRF 23, which is visually very close to the source. In Fill mode you also lose the cropped edges by design, so preview the result and switch to Fit if important content is being cut.

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