How private is local subtitle conversion?

CaptionShift reads the selected file in the browser. Its Content Security Policy blocks background network connections from the converter, but you should still use a trusted device and browser.

What privacy limitation remains?

Local processing does not make the file immune to other software, browser extensions, screen capture, or device access. CaptionShift itself does not upload the selected subtitle file.

Which files can I convert?

The converter supports SRT, WebVTT, SBV and ASS input and output, subject to the parser and format limitations described on the page.

Private browser processing

Convert Subtitle Files Without Uploading Them

CaptionShift is a local subtitle converter for SRT, WebVTT, SBV, and ASS files. It is useful when caption text is confidential or when you want to review a conversion without sending the file to a remote service.

Open the private converter Compare formats

What local processing means

The selected subtitle file is read by the browser, parsed into timing-and-text cues, shown in a preview, and converted into a local download. The converter’s Content Security Policy blocks background connections, and the product does not add analytics or advertising scripts.

Select file → parse locally → preview cues → choose output → download locally

Privacy is an architecture choice, not a promise that a device is risk-free. Browser extensions, other software, device access, and screenshots remain outside CaptionShift’s control.

Private conversion workflow

Use a trusted device and browser for the caption file.
Select one supported subtitle file up to 5 MB.
Check the visible cue preview and validation message.
Choose SRT, WebVTT, SBV, or ASS and apply a fixed offset only when appropriate.
Download the result and clear the page state when finished on a shared device.

Limitations to keep visible

ASS styling, fonts, positioning, effects, and script metadata may be lost in simpler outputs.
WebVTT cue settings and regions are not guaranteed to round-trip to SRT or other formats.
The converter does not translate, transcribe, process video, or repair synchronization drift.
Only the first 200 cues are shown in the preview; the file size limit is 5 MB.

Private subtitle questions

Does CaptionShift send my file to a server?

No. The converter processes the selected subtitle file in the browser, and the CSP blocks background network connections from the converter.

Should I use this on a shared computer?

Use a trusted device when possible. Clear the page state afterward and remember that browser history, extensions, screenshots, and other local access are outside the converter’s privacy boundary.

Does private processing preserve styling?

Privacy and format preservation are separate questions. Local processing prevents the converter from uploading the file, but conversion between formats can still discard unsupported styling or metadata.

CaptionShift overview · SRT to VTT · VTT to SRT · SBV to SRT · ASS to SRT · Suite homepage · Pricing · Account access · Privacy · Security