Convert files without uploading them: an alternative to CloudConvert and Convertio
Online converters like CloudConvert, Convertio or Zamzar share one architecture: your file goes up to their servers, gets converted there, and comes back down. It works, but you pay for it with upload time, daily limits or credits, and a copy of your file living on someone else’s machine.
Modern browsers can do most common conversions themselves. The tools below run WebAssembly builds of proven engines, such as FFmpeg, directly on your device: nothing is uploaded, there is no queue, and they keep working offline.
Side-by-side comparison
| Feature | CloudConvert | Convertio | Sunasty |
|---|---|---|---|
| Where your files are processed | On their servers: your file is uploaded | On their servers: your file is uploaded | In your browser: the file never leaves your device |
| Price | Free with limits, paid plans to lift them | Free with limits, paid plans to lift them | 100% free |
| Account | Required for some features | Required for some features | Never required |
| Works offline | No | No | Yes, once the page has loaded |
This comparison describes how each service is built (browser or server processing, free tier model). It deliberately avoids exact quotas and prices, which can change at any time. All product names belong to their respective owners.
Alternative to CloudConvert
CloudConvert is the powerhouse of the category: an enormous range of formats, processed on its servers, with a credit system where free usage is capped per day and volume is paid.
If your conversions are the common ones, images between JPEG, PNG, WebP or AVIF, audio between MP3, WAV, AAC or OGG, video between MP4, WebM or MKV, GIFs in both directions, the tools below do them locally, free and without waiting in line.
When CloudConvert is still the better choice
CloudConvert handles office documents, fonts and dozens of exotic formats that a browser cannot convert faithfully, and it offers an API for automated pipelines. For those jobs, a server-side service is the honest recommendation.
Alternative to Convertio
Convertio offers a similar catalogue with the same model: server-side conversion, a file size cap on the free tier, and a subscription to lift it. Zamzar plays in the same family.
The same logic applies: for everyday image, audio and video conversions, you do not need to send your file anywhere. Your browser can do the work itself, at the speed of your own machine.
When Convertio is still the better choice
If you need to convert directly from a URL, batch through an API, or handle document formats such as DOCX or EPUB, those remain server-side jobs where Convertio and its peers are the right category of tool.
The conversion tools you get here
- Video converter Convert video between MP4, WebM, MKV and MOV (H.264/H.265/VP9) in your browser. No upload.
- Audio converter Convert audio to MP3, WAV or AAC directly in your browser. No upload.
- Extract audio from MP4 Extract the audio track from your MP4 videos as MP3, without server-side conversion.
- Convert HEIC to JPG Convert iPhone HEIC/HEIF photos to JPG or PNG without uploading them.
- Video to GIF Convert a video clip into an animated GIF directly in your browser. No upload.
- GIF to video (MP4) Convert an animated GIF into a small MP4 video directly in your browser. No upload.
- Compress images Reduce image file size without uploading. Quality slider or target file size in KB. Batch supported.
- Images to PDF Combine one or more images (JPG, PNG, WebP) into a single PDF, right in your browser.
- Data Converter Convert data between JSON, YAML and CSV formats. No upload.
- Add audio to video Add or replace the soundtrack of a video with an audio file, in your browser. No upload.
Frequently asked questions
Why do most converters upload files at all?
Partly history, partly business model. These services predate what browsers can do today, and a server pipeline is easier to monetise: queues, daily limits and credits only make sense when the work happens on their side. WebAssembly moved that work onto your device.
Is converting in the browser slower?
The conversion itself runs on your machine, so a long video transcode depends on your hardware. But you skip the upload and the download of the result entirely, which is usually the slowest part for large files, and there is never a queue in front of you.
Which conversions can you not do?
Anything that needs a faithful office document engine: PDF to editable Word, DOCX to PDF, spreadsheets. Browser engines cannot reproduce these reliably, so we would rather not pretend. For media files, images, audio and video, the browser does the job.