How much smaller will my video actually get?

It depends heavily on the source. A video already compressed efficiently (recent H.264 or H.265 from a modern phone) might only shrink 15-25% at High Quality, while an older, less efficiently encoded file can shrink 50% or more at the same setting. Medium and Low presets push further, typically in the 40-80% range.

What exactly does CRF control?

CRF (Constant Rate Factor) tells the H.264 encoder how much perceptual quality to preserve. Lower numbers mean less compression and larger files; higher numbers mean more compression and smaller files. Unlike a fixed bitrate, CRF adapts per scene — simple, static scenes get very few bits, complex motion gets more — which generally produces better-looking results per byte than average-bitrate encoding.

Which preset should I use for uploading to social media?

Medium Quality (CRF 28) is usually the sweet spot for social platforms — most re-compress uploads anyway, so starting from a moderately compressed file rarely looks worse than uploading the full-size original, and the smaller file uploads faster.

Will compression make my video blurry?

At High Quality, most viewers see no visible difference. At Medium, very close inspection might reveal slight softening in fine detail. At Low, compression artifacts — blockiness and smearing in fast motion — become more visible, which is the trade-off for maximum size reduction.

Can I compress a video that is already MP4/H.264?

Yes. Re-encoding an already-compressed H.264 file at a higher CRF will still shrink it further, though because some quality was already lost in the original encode, you are compounding two rounds of lossy compression — the result will show more visible degradation than compressing a lossless or lightly compressed source.

Does lowering the resolution help more than adjusting CRF?

Often yes for dramatic size reduction. Halving both width and height cuts pixel count to a quarter, which typically has a much bigger effect on file size than moving between CRF presets, though it also means a permanently lower-resolution file rather than just more efficient compression of the same resolution.

Why is my compressed file barely smaller than the original?

This usually happens when the source was recorded with a very efficient modern codec (H.265/HEVC) and is being re-encoded to the less efficient H.264 at a similar visual quality — H.264 needs more bits than HEVC to look the same, which can offset some of the compression gain from raising CRF.

What format do I need to compress?

Any common video container works as input — MP4, MKV, AVI, MOV, or WebM. Regardless of the source format or original codec, the compressed output is always a standard H.264/AAC MP4.

Is there a limit on video length?

No hard length limit, but longer videos take proportionally longer to re-encode since every frame must be decoded and recompressed. File size, not duration, is what determines your plan's limit (40 MB guest, 80 MB free account, 250 MB Pro).

Is my video uploaded anywhere during compression?

No. FFmpeg WebAssembly performs the entire re-encode locally inside your browser tab. The file never leaves your device at any point in the process.

Compress Video — Free Online, No Upload

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Compression Quality

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What is Compress Video?

Video file size is mostly a function of one setting: how aggressively the encoder is allowed to discard information the human eye is unlikely to notice. H.264, the codec this tool uses, controls that trade-off through CRF — Constant Rate Factor — a single number from roughly 0 (lossless, enormous files) to 51 (unwatchable, tiny files). Rather than targeting an exact bitrate, CRF encoding lets the bitrate float scene by scene: a static talking-head shot needs very little data per frame, while a fast action sequence with lots of motion needs much more, and CRF automatically allocates more bits where the eye would actually notice the difference.

This tool offers three CRF presets tuned for different priorities. High Quality (CRF 23) is the same setting broadly considered visually transparent for most viewers, and typically shaves 20-30% off a file with negligible visible change. Medium Quality (CRF 28) pushes further, usually landing 40-60% smaller with only mild softening visible on close inspection, and is a good default when you need to fit under an upload limit. Low Quality (CRF 35) prioritizes size above all else, often reaching 60-80% smaller, with visible blockiness in high-motion scenes but is still watchable — useful when the alternative is not being able to send the file at all. Every preset re-encodes both video (to H.264) and audio (to AAC) and packages the result as a fast-start MP4.

How It Works

FFmpeg decodes your source video and re-encodes it with the libx264 encoder using the CRF value tied to your chosen preset — 23, 28, or 35. CRF encoding analyzes each frame's complexity and allocates bits accordingly rather than forcing a fixed bitrate, which produces better perceptual quality per byte than simple bitrate capping. Audio is re-encoded as AAC, and the -movflags +faststart flag places the file's index at the front so the result streams immediately in a browser rather than requiring a full download first. The whole process runs through FFmpeg WebAssembly inside your browser tab.

How to Use

Upload your video

Drop an MP4, MKV, MOV, AVI, or WebM file onto the upload area. The file is processed locally using FFmpeg WebAssembly.

Choose a compression preset

Select High Quality (CRF 23, best visuals), Medium Quality (CRF 28, balanced), or Low Quality (CRF 35, maximum compression).

Let FFmpeg load

The ~30 MB FFmpeg WebAssembly engine downloads once on first use and is cached for future conversions.

Click Compress Video

FFmpeg re-encodes the video using the CRF value tied to your chosen preset — this may take a minute or more for large or long files.

Watch the progress bar

Encoding time scales with video length and resolution, since every frame must be decoded and recompressed.

Review the savings

Once finished, the tool shows the exact percentage smaller the compressed file is compared to your original.

Download the compressed video

Save the result to your device. The original file is never modified or deleted.

Who Uses This Tool

📧

Beating Email Attachment Limits

Most email providers cap attachments around 25 MB — compress a phone-recorded clip down under that limit instead of switching to a separate file-sharing link.

📱

Freeing Up Phone Storage

Modern phones record 4K video that eats storage fast. Compress older recordings you want to keep but no longer need in full resolution.

🌐

Faster-Loading Website Videos

A hero background video or embedded demo clip that is too large slows down page load and hurts Core Web Vitals — compress it before uploading to your CMS.

📤

Meeting Platform Upload Caps

WhatsApp, Discord, and some forum upload forms enforce hard file-size ceilings — compress a video first rather than having the upload rejected outright.

💾

Shrinking a Video Archive

A folder of years of accumulated recordings can be run through Medium or Low presets to reclaim significant disk or cloud storage space.

🎓

Lecture and Course Video Hosting

Course platforms and self-hosted LMS systems often charge by storage or bandwidth — compressing lecture recordings before upload directly lowers hosting cost.

Why Choose This Tool

CRF Encoding, Not Fixed Bitrate

Bits are allocated per-scene based on complexity rather than forced into a flat bitrate, which generally produces better-looking results at the same file size.

100% Private Processing

H.264 re-encoding happens entirely in the browser via FFmpeg WebAssembly — no server upload required at any point.

Three Distinct Presets

High Quality for near-invisible compression, Medium for a strong size/quality balance, and Low for maximum shrinkage when size matters most.

See the Exact Savings

After compression finishes, the tool shows the precise percentage reduction and final file size, not just a vague "compressed" message.

Broad Input Support

Accepts MP4, MKV, AVI, MOV, and WebM — compress virtually any common video file regardless of its original codec.

Free — No Watermark

No watermark added to compressed output. Use free for files up to 40 MB, sign up free to raise your limit to 80 MB, or upgrade to Pro for 250 MB.

Key Benefits

Three CRF presets tuned for different size/quality trade-offs

Typical savings of 20-80% depending on preset and source

Adaptive per-scene bit allocation, not a flat bitrate cap

Browser-based — your video is never uploaded to a server

Shows the exact compression percentage after processing

Accepts MP4, MKV, AVI, MOV, and WebM as input

Output is a universally compatible H.264/AAC MP4

100% free with no watermark

Frequently Asked Questions

Free Online Document Tools for Everyone

iLoveDocsTools is used by students, professionals, and businesses across the United States, Canada, United Kingdom, Australia, India, and more than 100 other countries. All tools are browser-based and process files privately — your files never leave your device. Free to use, with Pro plans for unlimited access.

Compress Video

What is Compress Video?

How It Works

How to Use

Who Uses This Tool

Why Choose This Tool

Key Benefits

Frequently Asked Questions

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