Does resizing a video change its aspect ratio?

No. The tool automatically computes proportional dimensions to match your original aspect ratio so subjects are never stretched, squished, or distorted.

Why does the output video use even pixel dimensions?

H.264 compression processes pixels in 16x16 macroblock grids. Specifying odd dimensions causes encoder errors or visual glitches; snapping to even numbers ensures universal compatibility.

Can I upscale low-resolution video to 4K?

Yes, you can select higher resolution presets. However, upscaling increases file size without inventing new visual detail; resizing is most effective for downscaling large videos.

Is there any watermark on the exported video?

No. We believe your video belongs entirely to you. Output files contain no watermarks, timestamps, or promotional overlays of any kind.

Are my video files uploaded to any servers during resizing?

Never. All processing runs entirely inside your browser using client-side WebCodecs and canvas APIs under strict connect-src none Content Security Policies.

Resize Video Resolution

Scale video dimensions (4K, 1080p, 720p, 480p) in your browser. Aspect ratio preserved, no watermark.

100% Client-Side

About this video resizing tool

Select an MP4 or MOV video file, choose a target resolution preset (such as 1080p Full HD, 720p HD, 480p SD, or 50% scale), and click Resize Video. The video frames are decoded, scaled on a hardware canvas with aspect ratio preservation, and re-encoded via WebCodecs while the audio stream passes through untouched.

Downscaling high-resolution video recordings for social media distribution, web embedding, or bandwidth-constrained playback typically requires heavy video editing software or privacy-compromising cloud converters. This tool scales your video frames directly on your local GPU using HTML Canvas and browser WebCodecs hardware acceleration. It ensures macroblock-compliant even pixel dimensions, preserves audio tracks byte-for-byte, and exports clean MP4 files without watermarks.

Runs in this tab — no uploadFree, no account, no watermark

Step by step

1Load original videoSelect an MP4 or MOV video file up to 2 GB. The engine inspects container track headers to read the source display width, height, aspect ratio, and frame rate.
2Select target resolutionPick a resolution preset like 1080p, 720p, 480p, or 50% scale. The scaler computes proportional target dimensions, automatically rounding to even pixel counts required by H.264 macroblocks.
3Hardware canvas scaling and encodingClick Resize Video. Decoded frames are rendered onto an OffscreenCanvas with high-quality bicubic interpolation and fed directly into the hardware VideoEncoder with backpressure regulation.
4Download resized MP4Save the resized MP4 video. The newly generated visual sample entries (avc1 and avcC) and untouched audio packets are packaged into an updated MP4 container.

Aspect ratio preservation and macroblock alignment

Video compression standards like H.264 divide pictures into 16x16 pixel macroblocks. If a video is resized to an odd pixel dimension (such as 721 pixels wide), hardware encoders will either fail immediately with configuration errors or introduce green distortion bars along the edges. Our scaling engine calculates proportional dimensions that strictly preserve your source aspect ratio while snapping both width and height to the nearest even integer, guaranteeing clean hardware encoding and universal player compatibility.

GPU-accelerated canvas interpolation

Resizing video frames without blurring or aliasing requires high-quality image filtering. The engine renders decoded video frames onto an internal canvas context configured for smooth image smoothing. Downscaling 4K drone or camera footage to 1080p or 720p preserves sharp edges and fine image details without the jagged artifacts common in nearest-neighbor scaling algorithms, all while computing on your device graphics hardware.

Untouched audio passthrough without re-encoding

Changing the visual resolution of a video should never impact its audio clarity. Rather than decoding and re-compressing the soundtrack, this tool leaves the source audio stream completely untouched. AAC or MP3 audio packets are extracted directly from the input container and multiplexed into the output MP4 alongside the resized video frames. This prevents any audio generation loss, eliminates audio-video desynchronization, and cuts processing time significantly.

Dynamic AVC level management for standard and HD video

Different video resolutions require different H.264 profile and level constraints to ensure hardware decoders can allocate sufficient buffer memory. Scaling a 4K video down to 720p or 480p allows the encoder to use more efficient AVC levels (such as Baseline 3.1 or 3.0), drastically improving playback compatibility on older mobile hardware and low-power devices. The engine handles this parameter mapping dynamically based on target frame geometry.

Zero upload security guarantee

Every response from this site is served with a Content Security Policy whose connect-src directive is set to none. That is not a promise in marketing copy; it is an instruction to your browser, and the browser is the one enforcing it. While this page is open it cannot open a connection to anywhere — not to this site, not to anyone else — so there is no path by which your document could be uploaded, not by a bug, not by a future change, not by a script that should not be here. e2e/egress-proof.spec.ts asserts the served header and then tries to send data out by every route a page has and requires each attempt to be refused, and it runs on every build.

The second half of the guarantee is that the code has nowhere to send anything from. lib/tools/local-source-policy.test.ts reads every source file under lib/tools, workers, components and app on every test run and fails the build if any of them contains fetch, XMLHttpRequest, WebSocket, EventSource, sendBeacon or a peer connection, or even a remote address written down in a comment. A tool here cannot acquire an upload by accident, because the file that would have to contain one cannot be committed.

Client-side processing limits

Computations run directly on your own device using WebAssembly, Web Workers, and modern browser APIs including Web Crypto and TextDecoder. There are no server queues, no background telemetry, and no temporary cloud files created. Large operations remain responsive by offloading heavy parsing and conversion tasks to dedicated worker threads, ensuring the browser UI never freezes during intensive document and data processing tasks.

Questions people ask

Does resizing a video change its aspect ratio?: No. The tool automatically computes proportional dimensions to match your original aspect ratio so subjects are never stretched, squished, or distorted.
Why does the output video use even pixel dimensions?: H.264 compression processes pixels in 16x16 macroblock grids. Specifying odd dimensions causes encoder errors or visual glitches; snapping to even numbers ensures universal compatibility.
Can I upscale low-resolution video to 4K?: Yes, you can select higher resolution presets. However, upscaling increases file size without inventing new visual detail; resizing is most effective for downscaling large videos.
Is there any watermark on the exported video?: No. We believe your video belongs entirely to you. Output files contain no watermarks, timestamps, or promotional overlays of any kind.
Are my video files uploaded to any servers during resizing?: Never. All processing runs entirely inside your browser using client-side WebCodecs and canvas APIs under strict connect-src none Content Security Policies.

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