Reduce video size

Pick a quality or a target size in MB and a resolution cap; the video is re-encoded in your browser and the measured size is shown.

Pick a quality (Small, Balanced, High) or type a size to fit under in MB, optionally cap the resolution at 1080p, 720p or 480p or remove the sound, and Nerulio re-encodes the video in your browser: MP4 with H.264 when the browser can encode it, otherwise WebM with VP9, VP8 or AV1. A target is not a guess: the first pass is sized from the duration, and each later pass is corrected by the bytes actually produced, up to four passes, with the resolution lowered when bitrate alone cannot get there.

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Making a game?

Nerulio is a 2D game asset studio first: draw pixel art, cut sprite sheets into animations, pack texture atlases, check autotile tilesets and export them for Godot, Unity, Phaser and other engines. It runs in your browser; files stay on your device.

Open the game studio →All game tools GIF to sprite sheet Sprite animation preview Sprite sheet packer

What decides the size of a video

File size is bitrate × duration. A 60-second clip at 3 Mbit/s of video plus 192 kbit/s of audio is about 60 × 3.192 ÷ 8 ≈ 24 MB, whatever the resolution. Resolution and frame rate decide how good that bitrate looks: the same 3 Mbit/s spread over 1920 × 1080 must drop more detail per pixel than over 1280 × 720.

Without a target, the quality presets tell the encoder how hard to compress and the size follows from the content: a static talk shrinks a lot, confetti and grass do not. A source that was already compressed hard can even grow, and the result box then shows the increase in percent.

With a target, Nerulio budgets 95 % of it, subtracts the audio (bitrate × duration) and gives the rest to video. After each pass it measures the real video and audio bytes in the output, because browser encoders overshoot the bitrate they are asked for, and corrects the next pass. When lowering the bitrate stops paying off, it scales the frame down too. Below 50 kbit/s for video it refuses and asks for a bigger target or a shorter section.

Bitrate: Bits per second of a stream; video and audio add up. 1 Mbit/s for 60 s is 7.5 MB.
Resolution cap: Limits the output height: 720p keeps a 16:9 video at 1280 × 720 and turns a portrait 1080 × 1920 video into 404 × 718.
Pass: One complete encode. A target can take up to four, each one measured.

Example: fitting a 60-second clip under 25 MB

With the default 192 kbit/s audio:

Target          25 MB = 25 × 1,048,576 = 26,214,400 bytes
Budget (95 %)   24,903,680 bytes
Audio           192,000 bit/s × 60 s ÷ 8 = 1,440,000 bytes
Video, pass 1   (24,903,680 − 1,440,000) × 8 ÷ 60 = 3,128,490 bit/s ≈ 3.13 Mbit/s
If still over   next bitrate = current × (97 % of target − audio − container) ÷ video bytes produced
Passes 2–4      same correction; the width shrinks when the bitrate alone stops helping

"MB" here is 1,048,576 bytes, the same unit the result box uses. Removing the sound frees those 1.44 MB for the picture; lowering the audio bitrate under Advanced frees less.

Settings and what each one costs

Setting	What it does	Cost
Small / Balanced / High	Encoder quality level when no target is set	The size follows the content and can exceed a well-compressed source
Fit under (MB)	Measured passes until the file fits, up to four	Time; may lower the resolution
Resolution cap 1080p / 720p / 480p	Limits the output height and never upscales	Detail; portrait video becomes narrow
Remove sound	Drops the audio track entirely	No sound
Format MP4 / WebM (Advanced)	H.264 in MP4 when the browser has an encoder; otherwise VP9, VP8 or AV1 in WebM	Some apps accept only MP4

Check the result

The result box shows the size before and after and, with a target, whether it was met and how many passes it took.
Check the output dimensions there too: a smaller width than you chose means the target forced a smaller frame.
Play the result full screen and look at dark gradients, fast motion and small text, which show compression first.

Troubleshooting

Symptom	Likely cause	How to check	Fix
The result is larger than the original	The source was already compressed hard and the preset asked for more bits	The result box says it grew by a percentage	Choose Small, or set a target below the original size
"Target size leaves less than 50 kbit/s for video"	The target is too small for the duration once the audio is subtracted	Target ÷ seconds; audio alone takes 24 KB per second at 192 kbit/s	Raise the target, shorten the section, or remove the sound
The target was missed after four passes	The encoder could not go lower at the frame sizes tried	The result note reports the target and the actual size	Set a lower resolution cap yourself, or shorten the clip
An error says the audio alone needs more than the target	A long section at 192 kbit/s audio	The message names the kilobytes the audio needs	Lower the audio bitrate under Advanced, or remove the sound
MP4 is not offered	The browser has no H.264 encoder	Only WebM appears under Advanced	Use WebM, or another browser

Other ways to do it

Option	When it is the better choice
FFmpeg with libx264 and `-crf`	Constant-quality encodes, slower presets for smaller files and batch work; a size target means computing the bitrate yourself.
The export settings of the app that recorded or edited the video	When you still have the project: exporting once at the final size avoids compressing twice.
Trim first	When most of the clip is not needed, a shorter file is the cheapest reduction.

What this page does not cover

A target is measured, not guaranteed: after four passes the note says if it was missed.
The simple options do not lower the frame rate, and only the primary audio track is kept.

Versions and sources

Checked in tests/media-browser.mjs in Chromium 153 and Firefox 155 on a 1920 × 1080 test clip: an encode capped at 640 px came out 640 px wide and smaller than the source, and a 0.35 MB target was met with the width kept between 320 and 640 px. The measured correction exists because Firefox's H.264 and Opus encoders produced about 10 % and 9 % more than the requested bitrate. Engine: Mediabunny 1.58.1 with WebCodecs.

Official documentation used

MDN: Web video codec guide

Reduce video size

Pick a quality or a target size in MB and a resolution cap; the video is re-encoded in your browser and the measured size is shown.

How it works

Open the source file
Choose the processing mode and settings
Run, inspect the result and download

Supported formats

MP4 / WebM / MOV → MP4 / WebM — Input decoding and output encoding depend on browser support.

What this tool does

Control bitrate, dimensions and FPS; target-size estimates account for duration and audio.

Implementation and verified quality

advanced · WebCodecs bitrate and resolution control with measured size targets. Quality qualification is in progress. Pro/Flagship quality has not been established.

Before you export

Fast cut shrinks to inner keyframes. Precise mode re-encodes; codec availability varies. Temporary outputs use local browser storage when available. Compatibility recording retains its short-clip limits.

Frequently asked questions

What determines the supported size?

Actual device memory, storage and codec support. Tested examples are evidence, not a guarantee for every file.

Are my files uploaded?

This tool processes the files you open on your device without uploading them. Images you explicitly attach to community posts are uploaded separately. Optional engines and models are downloaded from third parties; those requests expose connection information such as your IP address.

Will my work be saved automatically?

No. Images and editing state stay in this tab; media output can use local temporary storage. Changing language preserves your work; reloading, closing the tab, or following a link to another page can clear it.