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StemStudio

Many at once

Batch file converter

Input

Convert many files at once, on your device (no upload)

← Just one file? Use the single converter

Drag & drop multiple files

or click to choose (multiple)

Result

No files yet. Add some and they appear here.

Convert a whole set of files and take them away as a ZIP.

How batch conversion works

A target per file
Every file you add becomes one row: its source format is detected and a suitable target is filled in. You can leave them all as suggested, or change the target on individual rows.
Collect the finished ones as a ZIP
Once two rows are done, a ZIP button appears. The ZIP is assembled inside your browser too, and nothing is sent anywhere. You can also save any row on its own.
One failure does not stop the rest
Rows are processed one at a time from the top. A file that could not be read simply shows "failed" on its row while the rest carry on. Anything this environment cannot produce a single target for is marked "unsupported" before the run and left out.

How to use

  1. Add the files

    Drag and drop several files at once, or click to choose them. Each file becomes one row, and its source format is detected there.

  2. Check the target on each row

    Every row arrives with a suitable target already filled in. Leave them as they are, or change the target from the picker on individual rows.

  3. Convert everything and take the ZIP

    Press convert and the rows are worked through one at a time from the top. Once two are done a ZIP button appears. You can also save any row on its own.

Glossary

What is a ZIP file?
A single archive holding several files. Windows, macOS and phones all open one without extra software. It also means one download instead of one per file.
What goes into the ZIP?
Only the files that finished converting. The originals are not in it, and neither are failed or unsupported rows. Each keeps its original name with only the extension changed.
What if two results end up with the same name?
The second and later ones get "(1)", "(2)" appended. Dropping in same-named photos from different folders will not make one of them disappear inside the ZIP.
What do "queued", "done", "failed" and "unsupported" mean?
Queued is a row still waiting, done is a row with a result you can save, failed is a row that stopped while reading or converting. Unsupported means there is no target this environment can produce from that file at all, so it is excluded from the run entirely.
Why are files converted one at a time?
Because images and audio are both expanded before being rewritten, and running many at once would consume all the memory at the same moment. In exchange for going in order, the button shows how many are finished.
Can I change a target afterwards?
Yes. Picking a different target on a finished row sends it back to queued, and pressing "convert all" again rebuilds it. While a run is in progress the selectors are locked so nothing is changed under you.

Frequently asked questions

Are the files uploaded when there are many of them?
No. However many you add, all of it happens inside your browser — including building the ZIP. Nothing leaves your device.
How many files can I add at once?
There is no fixed limit. But each file being converted is expanded into memory, so a large batch of big photos or long audio is more likely to fail partway, especially on a phone. A few dozen at a time is the safe way.
Why is there no ZIP button?
It does not appear while only one row is done, because a single file is quicker to take straight from that row's save button. It shows up once two or more have finished.
Can I mix images and audio in one batch?
Yes. The source is detected per row, so photos and voice memos added together each get a target that suits them, and they go into the same ZIP as they are.
Are the supported formats the same as single-file conversion?
They are. Output is PNG, JPG, WebP, WAV or MP3, and from a video only the audio is taken. The per-format detail lives on the file conversion page.
What happens if I close the tab partway?
The run stops and any results you have not saved are gone. Everything lives in the browser's memory, so there is nothing held server-side. Add the files again to start over.
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