Free Video Compressor & Converter

What Do CRF, Bitrate, and Encoder Presets Mean?

CRF — Quality Target

CRF (Constant Rate Factor) sets the perceptual quality target for every frame. H.264 accepts values 0-51; lower numbers mean higher quality and larger files. CRF 18-22 is near-lossless for archival. CRF 23-26 hits the sweet spot for streaming and sharing. CRF 28-35 produces small files suitable for preview clips where extreme compression is acceptable.

Encoder Speed Preset

The speed preset (ultrafast → veryslow) trades encoding time for compression efficiency. At the same CRF, a slow or veryslow preset produces a noticeably smaller file than veryfast because the encoder spends more time analyzing motion and choosing optimal block sizes. For desktop use, “medium” or “slow” is a practical default.

Resolution & Framerate

Halving the linear resolution (e.g., 4K → 1080p) cuts the pixel count to one-quarter, which typically reduces bitrate by 60-75% at equal quality. Framerate is preserved by default; dropping from 60 fps to 30 fps saves roughly 30-40% additional data for motion-heavy content. Cropping removes unwanted edges and reduces the total pixels the encoder must process.

How to Compress a Video Online in Four Steps

Video Compression FAQ — Common Questions Answered

Is it safe to compress videos online?

Yes, completely safe. Unlike traditional online compressors, LocalSquash processes your videos entirely in your browser using WebAssembly. Your files never leave your device, are never uploaded to any server, and remain completely private. No one else can access your videos.

How much can I reduce my video file size?

Typically, you can reduce video file size by 50-95% depending on your settings. Using a CRF value of 23-28 provides excellent quality while significantly reducing file size. Lowering the resolution (e.g., from 4K to 1080p) can reduce file size by 70% or more.

What video formats are supported?

We support almost all video formats including MP4, MOV (QuickTime), WebM, AVI, MKV, WMV, FLV, and more. Powered by FFmpeg, LocalSquash can handle virtually any video format you throw at it. The output is always MP4 with H.264 encoding for maximum compatibility across all devices and platforms.

What does CRF mean in video compression?

CRF (Constant Rate Factor) controls video quality. Lower values (18-23) produce higher quality and larger files, while higher values (28-35) produce smaller files with lower quality. We recommend CRF 23-26 for most use cases, offering a good balance between file size and visual quality.

Can I compress 4K videos?

Yes! You can compress 4K videos and optionally downscale them to 1080p or other resolutions for even greater file size reduction. Keep in mind that processing 4K videos requires more time and memory.

Is there a file size limit?

The only limit is your device's available memory. Since processing happens in your browser, very large files (over 2-4GB) may be slow or fail on devices with limited RAM. For best results, we recommend files under 2GB.

Will compressing reduce video quality?

Some quality loss is inevitable with compression, but with proper settings (CRF 23-26), the difference is barely noticeable to the human eye. You can preview the expected file size before compressing to find the right balance for your needs.

How do I compress video for Discord?

To compress video for Discord's 8MB or 50MB limit: 1) Upload your video, 2) Set CRF to 28-32 for maximum compression, 3) Reduce resolution to 720p or lower if needed, 4) Trim the video to essential parts. This typically achieves the small file sizes required for Discord.

How do I compress video for email?

For email attachments (usually 25MB limit): 1) Upload your video, 2) Use CRF 26-30, 3) Consider reducing resolution to 720p, 4) Trim any unnecessary parts. For longer videos, consider sending a link instead.

Can I trim and crop videos?

Yes! LocalSquash includes trim and crop features. You can cut your video to a specific time range and crop to various aspect ratios (16:9, 9:16 for TikTok/Reels, 1:1 for Instagram, etc.) before compressing.

Is LocalSquash a good HandBrake alternative?

Yes. LocalSquash uses the same FFmpeg H.264 encoder as HandBrake but runs entirely in your browser — no download or install required. You get the same CRF quality control, speed presets, and format support. HandBrake is better for batch processing and advanced codec options (like H.265/AV1), but for quick single-file compression, LocalSquash is faster to get started with since it works instantly in any browser.

How do I convert WebM, MKV, or MOV to MP4?

Simply upload your WebM, MKV, or MOV file to LocalSquash. The tool automatically converts any input format to MP4 with H.264 encoding during compression. This is equivalent to running 'ffmpeg -i input.webm output.mp4' but with a visual interface and no command-line knowledge required. Supported input formats include WebM (VP8/VP9), MKV (Matroska), MOV (QuickTime), AVI, WMV, FLV, and more.

What CRF value gives the best quality-to-size ratio?

For H.264, CRF 23 is the encoder's default and an excellent starting point. CRF 18 is considered visually lossless by most viewers. Going above CRF 28 starts to introduce blocking artefacts in fast-motion scenes. For footage destined for Discord or WhatsApp (where file size caps apply), CRF 28-32 with a lower resolution typically produces the best result within the size constraint.

How does the encoder speed preset affect quality?

The preset does not change the target quality set by CRF; it changes how efficiently the encoder reaches that quality level. A slower preset (slow, veryslow) uses more advanced motion estimation and reference frame analysis, producing a smaller file at the same CRF value. For browser-based encoding, "medium" or "fast" is recommended because slower presets can take 10-30 minutes for longer clips.

How much does resolution affect file size?

Resolution has a quadratic effect on bitrate. Downscaling from 3840x2160 (4K) to 1920x1080 (1080p) reduces the pixel count by 75%, meaning the encoder needs roughly one-quarter of the bitrate to achieve the same CRF score. In practice this equals a 60-75% reduction in output file size for the video stream, before accounting for audio.

Should I lower the audio bitrate too?

For most video content, audio represents 5-15% of total file size. Dropping audio from 192 kbps to 128 kbps saves about 4-6 MB per minute of video, which is worthwhile when working near a file size limit. For voice-heavy content (interviews, tutorials), 96 kbps AAC is transparent. For music-driven content where fidelity matters, keep audio at 192 kbps or higher.

Can I compress a 4K or HDR video?

Yes. LocalSquash accepts 4K UHD and HDR source files. Because encoding happens in software (not hardware), a 4K re-encode at medium preset can take 20-60 minutes depending on clip length and your CPU speed. For HDR sources, the output is encoded to SDR H.264, which means tone mapping is applied automatically by FFmpeg. If you want to preserve HDR metadata, download the original and use a desktop encoder like HandBrake instead.

What output format does LocalSquash produce?

Output is always an MP4 container with H.264 video (libx264) and AAC audio. This combination has the widest device compatibility in existence — it plays on iOS, Android, Windows, macOS, Linux, all major browsers, smart TVs, and game consoles without any additional codec installation.

Convert WebM, MKV & MOV to MP4 — FFmpeg in Your Browser

Need to convert WebM to MP4, convert MKV to MP4, or convert MOV to MP4? LocalSquash handles all three with the same FFmpeg engine used by professionals on the command line. Instead of typing ffmpeg -i input.webm output.mp4, simply drag your file onto the upload area. The conversion produces H.264 MP4 with AAC audio — the most universally compatible format across all devices and platforms.

How to Get the Smallest Video File Size