Attach a Video to the Subtitle Workbench: What Changes, and What the Export Still Gives You

Attach a Video to the Subtitle Workbench: What Changes, and What the Export Still Gives You

I work on OnePassApps - the team behind app.onepassapps.com - so this is our own app, and every number below is something I measured on it myself today, 10 November 2026, in a signed-out browser session. The tool is the Subtitle Workbench: https://app.onepassapps.com/apps/subtitle-workbench?utm_source=devto&utm_medium=blog&utm_campaign=subtitle-reference-media&utm_content=subtitle-link

I started with the app's own Load example button, which loads a sample subtitle file, and then I attached a real two-second MP4 through the app's own reference-media control - the file input labelled Choose reference media. The MP4 was one I made myself with ffmpeg: 5,022 bytes, H.264 video, AAC audio.

Attaching it changes the panel in three visible ways. A media chip appears: Reference media · 0:01 · 4.9 KiB. Two controls appear next to the file: Replace ref-media.mp4 and Remove ref-media.mp4. And a player appears inside the panel, with the line Space plays or pauses. I and O set the selection at the playhead. and a position readout of 0:00.0 / 0:02.0.

The player really plays. I pressed its Play button with a real mouse press and the readout moved from 0:00.0 to 0:01.3 against the same 0:02.0 total.

One thing I did not expect: the two readouts of that file's length disagree. The chip says 0:01, the player's own readout says 0:02.0, and ffprobe reads the same file's duration as 2.000000 seconds. So the panel shows two different lengths for one file, and I can only report that they differ.

What did not change is the export. I exported SRT before attaching the media and again after, and the two files were byte for byte the same: the same name, the same 137 bytes and the same SHA-256, e079faf0bd98b5d565c4b6a29e14293c02e443eec5aaa5583b878498e39e8fab. Attaching a video gives you a surface to check your cues against - a timeline, a playhead, a position - and it does not put anything of the video into the subtitle file.

Nothing left the tab. The panel says the reference media stays in this tab, and the session I traced made 91 requests, every one of them a GET, none of them carrying a request body, to app.onepassapps.com, api.onepassapps.com and clerk.onepassapps.com.

What I did not do: I did not press I or O to set a selection at the playhead, so I make no claim about what that does to a cue. I did not test the WebVTT export format, the Export all ZIP button, or the Download original control. And my media file was a two-second clip I generated - it has no dialogue in it, so nothing here is a claim about how cues line up with real speech.

I wrote up more on subtitle timing and the repair order in the browser on Dev.to: https://dev.to/onepassapps/the-repair-order-in-the-browser-subtitle-editor-four-checkboxes-one-sequence-and-a-measured-shift-5gfb . I write here as the OnePassApps team, so questions about how the apps work are welcome - and corrections are better than praise.

The same write-up went out on Telegraph earlier today, and that is the canonical copy: https://telegra.ph/Attach-a-Video-to-the-Subtitle-Workbench-What-Changes-and-What-the-Export-Still-Gives-You-11-11 . This is the same measurement, published here on Dev.to.