Video Aspect Ratio Changer
Change video aspect ratios to 9:16, 1:1, or 16:9 by padding or cropping frames. Adjust dimensions directly in your browser without uploading to any server.
MP4, WebM, MOV, MKV, AVI, FLV, 3GP · up to 1 GB
Tips
- The browser downloads a 30 MB processing engine once on initial launch, enabling subsequent offline conversions.
- Padding mode preserves the entire original frame by adding letterbox bars, while cropping removes outer edges to fill the screen.
- Using a blurred background fill instead of solid black bars creates a cleaner visual presentation for vertical video formats.
How to use it
- 1 Select and load your video file into the workspace.
- 2 Choose your target aspect ratio such as 9:16, 1:1, or 16:9.
- 3 Select a framing mode between cropping the edges or adding padded borders.
- 4 Process the video and download the re-encoded file to your device.
What you should know
Different platforms demand distinct display geometries, ranging from 16:9 widescreen for desktop players to vertical 9:16 for mobile feeds and square 1:1 for marketplace listings. Changing aspect ratios requires re-encoding the video stream to adapt pixel dimensions while avoiding unwanted distortion. Standard video containers like MP4 with H.264 codecs require even-numbered pixel dimensions for macroblock alignment. Without deliberate reframing or padding, forcing a video into a new container size stretches the pixel aspect ratio, distorting subjects and ruining visual composition across varying mobile and desktop displays.
This tool processes your video entirely inside your browser using WebAssembly to pad or crop footage into preset or custom ratios. You can select standard proportions such as 9:16, 1:1, 4:5, or 16:9, and choose between solid matte borders, blurred edge fills, or center-weighted cropping. Because the engine runs locally and single-threaded, re-encoding long high-definition files requires processing time proportional to the video duration. The output preserves audio tracks while writing a fresh video stream, but non-standard container metadata and multiple subtitle tracks are discarded during export.
Frequently asked questions
Does changing the aspect ratio lower video quality?
Re-encoding the video stream applies standard lossy H.264 compression to generate the new frame dimensions. Setting higher quality parameters minimizes compression artifacts while matching the target canvas size.
Why does processing take longer for high-resolution or long videos?
The underlying engine runs inside your browser using a single CPU thread to decode, resize, pad, and re-encode every frame. Performance depends entirely on your local device hardware rather than an external server.
Are my videos uploaded or stored anywhere?
No, your video never leaves your computer or phone. All transformations happen locally in browser memory through client-side WebAssembly execution.
Guides
Articles and format references related to this tool.
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