How does browser-based file conversion work?

Convertlo uses WebAssembly — a high-performance binary instruction format that runs in the browser — to execute conversion libraries directly on your device. Images use the HTML5 Canvas API. Audio and video use FFmpeg.wasm, a port of the professional FFmpeg tool to WebAssembly. Documents use PDF.js and docx.js. All processing runs locally; no data is ever transmitted to a server.

What formats does Convertlo support?

Convertlo supports 190+ conversion formats: 73 image formats (JPG, PNG, WebP, AVIF, HEIC, SVG, BMP, GIF and more), 43 document formats (PDF, DOCX, XLSX, CSV, TXT, HTML and more), 30 audio formats (MP3, WAV, FLAC, AAC, OGG, M4A and more), and 45 video formats (MP4, WebM, MOV, AVI, MKV, WMV and more). Browse all converters at convertlo.pro/tools.html.

100% browser-based · no uploads

Free Online File Converter
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Q: What is the maximum file size?

50 MB per file — images and documents convert quickly at this size; video files may take 30–60 seconds on slower devices. All processing is in-browser so performance depends on your device.

Q: Can I convert multiple files at once?

Yes — enable the Batch convert toggle in the options panel, then select or drop multiple files. All files in a batch must be the same format type. Each file is converted and downloadable individually.

Q: Does Convertlo work offline?

Yes — after loading the page once, image and document conversions work completely offline. Audio and video conversions require FFmpeg.wasm (~32 MB) to be cached on first use, after which they also work offline. A service worker caches all assets automatically.

Convert images, documents, audio & video — 100% in your browser. Files never leave your device. No server, no signup, no cost.

From

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Drop your image here

or click to browse · JPG, PNG, WebP…

Browse file

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Conversion options

Quality 85%

Batch convert

Upload multiple files at once

Image tools

Width (px)

Height (px)

Leave blank to keep original dimensions

Load an image, then switch to this tab to crop visually

⬆ Drop a file above or click to browse, then hit Convert

Uploading file… 0%

⚠ Error

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ℹ Notice

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✅

Conversion complete!

Your file is ready.

⬇ Download file

📦

Batch conversion complete!

All files converted.

100+Formats

50 MBPer file

0Data sent

No signupEver

FreeForever

Conversion history

No conversions yet — your history will appear here.

Popular conversions

Most-used tools — click to open directly.

JPG → WebP→ PNG → JPEG→ MP4 → MP3→ BMP → PNG→ HEIC → JPG→ JPG → PDF→ PDF → JPG→ WebP → JPG→ PNG → WebP→ SVG → PNG→ MP4 → WebM→ PDF → PNG→

Supported conversions

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Images

JPG · PNG · WebP · AVIF · HEIC · GIF · BMP · SVG · PDF

Exact re-encode — pixel-perfect output, full quality control

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Documents

TXT · HTML · CSV · JSON · XLSX · DOCX · MD · PDF

Text extraction — content is preserved, complex layout is not

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Audio

MP3 · WAV · OGG · M4A · AAC · FLAC → WAV · MP3

Exact transcode — lossless WAV or compressed MP3, your choice

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Video

MP4 · WebM · GIF · MOV · AVI · MKV · FLV · WMV

Re-encode or extract — convert format, pull audio, or make GIFs

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Compress

JPG · PNG · WebP — batch supported

Up to 90% smaller with no visible quality loss

How it works

Pick your formats

Choose your input and output format from our library of 70+ converters — images, documents, audio, and video all supported.

Drop your file

Drag and drop or click to browse. Conversion starts instantly — everything runs inside your browser using JavaScript. Nothing is uploaded.

Download instantly

Your converted file is ready in seconds. Download it directly to your device. No account, no email, no waiting. 100% free forever.

Frequently asked questions

Is it really private? Does anything get uploaded?

Yes, completely private. Every conversion happens inside your browser using JavaScript. Your files are never sent to any server — not even ours. You can disconnect from the internet after the page loads and conversions will still work.

What is the maximum file size?

50 MB per file — though the practical limit depends on your device and file type. Images and documents convert quickly even at 50 MB. Audio files up to 50 MB work well on any modern device. Video files are the most memory-intensive: a 50 MB MP4 may take 30–60 seconds on slower devices. If a conversion stalls, try a smaller clip or use a more powerful device.

Why does the first video conversion take so long?

Video conversions use FFmpeg.wasm, a ~32 MB library that has to be downloaded once on first use. After that it's cached in your browser and future conversions start instantly. Audio and image conversions start immediately with no downloads.

Does it work offline?

Yes — once you've visited the page, Convertlo installs as a Progressive Web App and caches itself. Image, audio, and document conversions work fully offline. Video conversions require the FFmpeg library to be cached first (happens automatically on first use).

Does PDF → image export all pages or just the first?

All pages. When you convert a multi-page PDF to JPG or PNG, every page is exported as a separate image and automatically bundled into a ZIP file you can download in one click.

Is Convertlo free? Are there any limits?

Completely free, no account required. There are no conversion limits, no watermarks, and no hidden paid tiers. The only limits are the 50 MB file size cap and what your browser can handle in memory.

Can I convert multiple files at once?

Yes — enable the "Batch convert" toggle in the options panel, then select or drop multiple files. All files in a batch must be the same format type. Each file is converted and downloadable individually.

What browsers are supported?

Chrome, Edge, Firefox, and Safari (desktop and mobile). Chrome and Edge give the best performance. Safari on iOS supports all conversions except video (FFmpeg.wasm requires SharedArrayBuffer which Safari limits on some versions).

People Also Ask

Is It Safe to Convert Files in a Browser?

Browser-based conversion is actually safer than uploading files to a server. Convertlo processes everything locally using WebAssembly — your files never leave your device and are never transmitted over the internet. There is no server that could be hacked, no database storing your files, and no third party with access to your data. The conversion happens entirely within your browser's sandboxed environment, the same security model that protects your banking and email sessions.

What Is the Difference Between Lossy and Lossless Conversion?

Lossy conversion (JPG, WebP lossy, MP3) permanently discards data to achieve smaller file sizes. The discarded data is chosen based on what human perception is least sensitive to — you may not notice the difference, but it cannot be recovered. Lossless conversion (PNG, FLAC, WebP lossless) preserves all original data exactly — output files are larger but identical in quality to the source. For web images, lossy WebP at 80% quality is typically indistinguishable from the original while being 25–35% smaller than JPEG. For archiving, always use lossless formats.

Does Browser-Based Conversion Work Offline?

Yes. After you load Convertlo once, a service worker caches all assets locally. Image and document conversions work completely offline from that point. Audio and video conversions require FFmpeg.wasm (~32 MB) to be cached on first use — after that they also work offline. This makes Convertlo useful on planes, in areas with poor connectivity, or anywhere you need to convert files without a reliable internet connection.

How Many Formats Does Convertlo Support?

Convertlo supports 190+ conversion formats: 73 image formats (JPG, PNG, WebP, AVIF, HEIC, SVG, BMP, GIF and more), 43 document formats (PDF, DOCX, XLSX, CSV, TXT and more), 30 audio formats (MP3, WAV, FLAC, AAC, OGG and more), and 45 video formats (MP4, WebM, MOV, AVI, MKV, WMV and more). The full list is available at the All Tools directory.

Is a Browser Converter as Good as Desktop Software?

For most common conversions — images, PDFs, audio files under 100 MB — yes. Convertlo uses the same underlying engine as many desktop tools: FFmpeg for audio/video (the engine behind VLC, Handbrake, and most professional video software) and Canvas API for images. The main advantages of desktop software are processing speed for very large files and access to advanced encoding settings. For everyday file conversion needs, browser-based tools are faster to use, require no installation, and are completely private.