Does Subformer upload my file to a server?

No. Every conversion runs entirely in your browser. Your file never leaves your device - no upload, no server processing, no tracking of the file content.

Which formats can I convert?

Video: MP4, MOV, MKV, WebM. Audio: MP3, WAV, OGG, AAC, M4A. Images: JPG, PNG, WebP, HEIC, BMP, GIF. Documents: PDF (input and output). Most common audio codecs (AAC, MP3, Opus, Vorbis, FLAC, PCM) are accepted as media input.

Can I combine JPGs into a PDF?

Yes. Drop one or more JPG or PNG files and pick PDF as the output - each image becomes a page in a single PDF. We embed the original image bytes without re-encoding, so there's no quality loss.

Can I convert HEIC photos from my iPhone?

Yes. Pick HEIC to JPG, HEIC to PNG, or HEIC to PDF. The converter uses a WebAssembly libheif build to decode HEIC locally - your photos never leave your device.

Can I convert MP4 to MP3?

Yes. Pick an MP4 (or any video file) and choose MP3 as the output. The converter extracts and re-encodes the audio track locally.

Can I convert MOV to MP4?

Yes - and it's fast. MOV and MP4 share the same underlying container, so most MOV to MP4 conversions are remuxes without re-encoding video.

Is there a file size limit?

No server-side limit - nothing is uploaded. Files over 500 MB trigger a warning because browsers can run out of memory on very large files.

Which browsers are supported?

Any modern browser: Chrome 94+, Edge 94+, Firefox 130+, Safari 16.4+. Image and PDF conversions also need WebAssembly support, which every modern browser has.

Can I convert multiple files at once?

For image-to-PDF, yes - drop several images and we combine them into a single PDF. For other conversions, batch is on the roadmap. You can open multiple browser tabs in parallel as a workaround.

What's the difference between the WebCodecs and FFmpeg engines?

Both engines (used for video and audio) run entirely in your browser - no file is ever uploaded. WebCodecs is the default: it uses your browser's hardware-accelerated media APIs so conversions are fast and ship no extra wasm. FFmpeg (wasm) is a pure-software fallback built from the same ffmpeg project desktop tools use - it supports more codecs but is slower and downloads ~22 MB on first use.

When should I pick the FFmpeg engine?

Switch to FFmpeg if the WebCodecs engine fails with an 'unsupported codec' error, if your browser lacks a decoder (e.g. older Safari with VP9), or if you need strict H.264 + AAC output for maximum device compatibility. For everyday MP4 / MOV / MKV / WebM / MP3 / WAV conversions, WebCodecs is faster and recommended.

Is FFmpeg-wasm safe to run in the browser?

Yes. @ffmpeg/ffmpeg is an open-source WebAssembly build of the official FFmpeg project. It runs inside the browser sandbox with no network access - all processing happens on your device. We fetch the wasm core once from a public CDN and execute it locally.

Subformer

Free · No signup · Runs in your browser

Free Online File Converter

Convert video, audio, images, and PDFs entirely in your browser - MP4, MOV, MP3, WAV, JPG, PNG, HEIC, PDF, and more. Fast, private, nothing is uploaded.

Drop one or many - video, audio, image, PDF, subtitles, data, documents. Per-file targets, batch convert, ZIP download.

Pick a category to get started

Each conversion has a dedicated page with format-specific tips. Pick the closest match for what you need.

How to convert a file online

01
Drop your file
Drag a video, audio, image, or PDF onto the converter - or click to pick one from your device.
02
Choose the output format
Pick a one-click preset or open a dedicated conversion page (JPG to PDF, HEIC to JPG, MP4 to MP3, and more).
03
Convert and download
Click Convert. The browser handles the rest - watch the progress bar, then download your new file.

Everything you need to convert files

Private by design

Your file never leaves your device. Decoding, encoding, and writing all happen in your browser - we can't even see the filename.

Hardware-accelerated

Video and audio go through WebCodecs - the same engine your browser uses for YouTube and Netflix. Image and PDF flows use canvas + pdf-lib, also fully GPU-friendly.

Image & PDF support

Combine JPGs into a PDF, convert HEIC photos from your iPhone, render PDF pages as images, or move between JPG, PNG, and WebP.

Video ↔ audio extraction

Upload a video, pick an audio format, and get just the audio. Great for turning talks, lectures, and podcasts into MP3s.

MP4 fast-start

MP4 output is produced with its moov atom at the start of the file - ideal for streaming and direct web playback.

Zero install

No desktop app, no plugin, no command-line ffmpeg. Open the page, drop a file, get a result.

Cancel anytime

Conversions run in the background of the tab and can be cancelled mid-way if you change your mind.

Supported formats

The converter reads most common file types and exports to any of the formats below.

Video

MP4 - Most compatible container. Works everywhere. Produced with fast-start for quick web playback.
MOV - QuickTime container. Same structure as MP4 - fast remuxing.
MKV - Matroska. Flexible container used by many sources.
WebM - Web-native format, great for online video with VP8 / VP9 / AV1.

Audio

MP3 - Universally supported. Good pick for podcasts and music sharing.
M4A / AAC - AAC audio in an MP4 container (M4A) or raw ADTS stream. Common on Apple devices.
WAV - Uncompressed PCM audio. Great for editing workflows.
OGG - Open-source container, usually with Opus or Vorbis audio.

Image

JPG - The dominant lossy format on the web. Small files, near-universal support, no transparency.
PNG - Lossless with alpha-channel transparency. Best for screenshots, logos, and graphics.
WebP - Modern Google format. Beats JPG and PNG on file size at the same quality.
HEIC - Apple's default iPhone photo format. About half the size of JPG - we decode it locally via WebAssembly libheif.

Document

PDF - Universal document format. Embed JPG / PNG / HEIC images into a single PDF, or render PDF pages back to images. Multi-page PDFs come out as a ZIP of pages.

Text & Subtitles

TXT / Markdown - Plain text and Markdown. Convert to PDF for printable distribution. Markdown headings, lists, and bullets render with basic styling.
SRT / VTT - Subtitle and caption files. Convert between SRT and WebVTT, or strip timestamps to get plain-text transcripts.

Data & Spreadsheets

CSV / JSON / YAML - Tabular and structured data formats. Convert between any two for scripts, APIs, and config files.
XLSX (Excel) - Excel spreadsheets. Extract data to CSV or JSON for scripting and data pipelines.

All conversions

Dedicated one-click pages with format-specific guidance for every conversion we support.

Pick a category to get started

Video

Audio

Image

PDF & Documents

Text & Subtitles

Data & Spreadsheets

How to convert a file online

Drop your file

Choose the output format

Convert and download

Everything you need to convert files

Private by design

Hardware-accelerated

Image & PDF support

Video ↔ audio extraction

MP4 fast-start

Zero install

Cancel anytime

Supported formats

Video

Audio

Image

Document

Text & Subtitles

Data & Spreadsheets

All conversions

Video & Audio

Image & PDF

Text & Subtitles

Data & Spreadsheets

Documents

Compress

Frequently asked questions

Does Subformer upload my file to a server?

Which formats can I convert?

Can I combine JPGs into a PDF?

Can I convert HEIC photos from my iPhone?

Can I convert MP4 to MP3?

Can I convert MOV to MP4?

Is there a file size limit?

Why does the first MP3 conversion take a moment on Firefox?

Which browsers are supported?

Can I convert multiple files at once?

What's the difference between the WebCodecs and FFmpeg engines?

When should I pick the FFmpeg engine?

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