Check the audio track inside an MP4
Choose a local MP4 up to 100 MB above. Transcription reads a decodable English audio track; visible captions, slides and silent images do not become speech.
1. Does this MP4 contain usable speech?
Play the actual file with sound first. MP4 is a container: a playable picture alone does not prove the audio codec is decodable here. A silent screen recording needs another source if you need spoken words. The browser first decodes the recording, checks its language with a multilingual checkpoint, then recognizes English with a separate English checkpoint. First use may download both models. Cached resource files can avoid another download, but they do not guarantee an initialized model: the English instance is released before the next language check. There is no fixed completion time.
Check: The intended passage has audible English speech.
Back to the tool2. How do I compare the result with the picture?
Use the local video player and replay an important phrase. Read on-screen labels separately; this workflow does not run OCR or extract an embedded subtitle track. Click a transcript timestamp to seek in the local recording player. Replay the surrounding phrase before editing its cue. Text edits do not move cue boundaries. Use Find in this transcript to locate an exact word in the latest edits; Previous and Next navigate matches, Enter moves forward, Shift+Enter moves back, and Escape clears the search.
![How do I compare the result with the picture? Actual local sample workflow. Any [reviewed] suffix is a deliberate teaching edit, not recognized speech.](/assets/tutorials/mp4-to-text/02-review-narrow.svg)
Check: A visible title has not been mistaken for recognized speech.
Back to the tool3. How do I deliver text or a subtitle track?
TXT is a reading copy. SRT/VTT is a separate subtitle artifact; exporting it does not render captions into the MP4. The Video to Text walkthrough covers the full general video workflow. Copy, TXT and Markdown use your edited words and are untimed by default. Enable Include timestamps in TXT, Markdown and Copy to include available start times. Markdown escapes markup and exports transcript paragraphs, without creating a summary. SRT, VTT and Open in Subtitle Editor require nonempty text and complete valid start/end times; missing ends are not estimated. If timing is incomplete, save TXT or Markdown and keep the recording.
![How do I deliver text or a subtitle track? Actual local sample workflow. Any [reviewed] suffix is a deliberate teaching edit, not recognized speech.](/assets/tutorials/mp4-to-text/03-save-narrow.svg)
First cue from the actual teaching export (including the deliberate [reviewed] edit):
1 00:00:00,000 --> 00:00:07,740 And so my fellow Americans ask not what your country can do for you [reviewed]
Check: The subtitle file is checked against the same MP4 edit in its destination.
Back to the toolMore questions and limits
Does my recording leave this device?
Local decoding, recognition, replay, edits and downloads run in your browser. Model resources need network access, but the local recording and transcript are not uploaded. There is no account history or saved cloud project; download your work before closing the tab. Same-origin editor transfer keeps the cues and recording local between tabs. Instagram URL retrieval and YouTube caption lookup have separate server-assisted privacy boundaries.
What if decoding or the language check fails?
An undecodable file is different from a language result. Detected non-English speech stops recognition; an uncertain result or a technical language-check failure stops with a separate message and creates no transcript. For a damaged or unsupported file, export a new playable audio copy from its source: renaming the extension does not convert it. Recording Format Guide explains these boundaries.
Can I cancel and try again?
Only one transcription task runs at a time. Cancel processing discards its result; an in-progress model or audio operation may need to finish before controls unlock. Then use Try the same input again. Choosing another input clears the previous retry target. A cancellation is not a transcript of silence.
Where is the complete audio workflow?
Audio to Text explains search, text corrections and output choices. For timing changes, use Subtitle Editor.
Historical measurements and method limits
Measured browser timings
These are historical measurements from 2026-09-14 using only whisper-tiny.en. They do not measure the current language-detection plus English-transcription workflow, and exclude Instagram lookup and media download.
| Audio length | Historical wall-clock time | Historical model load |
|---|---|---|
| 11 s | 16.89 s | included |
| 11 s | 6.49 s | already in memory |
| 30 s | 8.98 s | already in memory |
| 60 s | 16.06 s | already in memory |
| 120 s | 28.58 s | already in memory |
In the historical test, the first run included model loading; subsequent runs retained the English model in memory. Current jobs release that instance before language detection, so a resource cache hit still requires initialization. Wall-clock time is not CPU time, and subtracting two runs does not isolate download or initialization time.
One machine, one WASM browser, one run per historical data point. Audio clips were constructed from a repeated public JFK recording. These rows do not predict today's end-to-end time, other devices or other recording content.
Sources: historical raw CSV · current two-model measurements (2026-10-14) · method, environment and limitations.