How to convert MP4 to SRT — fastest ways to generate captions

An SRT (SubRip) file is the universal subtitle format. Once you have one, you can upload it to YouTube, Vimeo, Teachable, LinkedIn, or any platform that supports captions. You can translate it into any language. You can publish it as a transcript on your blog. The MP4 → SRT step is the gateway to all of those workflows.

Option 1 — SoCaptions MP4 to SRT workflow (fastest)

1. 01Open the SoCaptions editor and upload your MP4.
2. 02Drop your MP4. The tool extracts the audio and runs it through Whisper.
3. 03Wait 30–90 seconds for short clips, 2–4 minutes for longer recordings.
4. 04Download the .srt file. Done.

The output uses Whisper's word-level timing, which is accurate to ±50ms. That means the SRT will sync cleanly with the original video without manual timing fixes.

Option 2 — Whisper locally (free, slower)

If you have a Mac with Apple Silicon or a CUDA-capable GPU, you can run Whisper locally and generate SRT files for free. Install whisper.cpp or the openai-whisper package, point it at your MP4, and pass --output-format srt.

• Pros: free, private, offline.
• Cons: setup takes 15–30 minutes the first time. Slower than cloud Whisper unless you have a strong GPU.
• Best for: large back-catalogs you do not want to upload.

Option 3 — manual SRT in a text editor (slowest)

Open the MP4 in VLC or QuickTime, scrub through it, and type each caption with manual timestamps in a .srt file. The format is simple — index, start --> end, dialogue, blank line, repeat. This is the slow path but it gives you exact control.

After you have the SRT

1. 01Review proper nouns, product names, technical terms, numbers, and URLs. AI gets these wrong most often.
2. 02Check timing on the first and last 30 seconds — drift is most visible there.
3. 03Convert to VTT if you need it for HTML5 video. Convert to ASS only if you need styling baked into the file.
4. 04Translate to any language using a translation tool or service. The SRT structure preserves automatically.

Common errors and fixes

• Captions appear out of sync: shift the entire SRT by a constant offset using the SoCaptions Subtitle Timing Shifter.
• Captions cut off mid-sentence: use the Subtitle Line Splitter to reflow long lines.
• Reading speed too fast: run the SRT through the Reading Speed Checker to flag cues that exceed 17 CPS.
• Wrong frame rate: use the Frame Rate Converter when re-targeting from 23.976 fps to 25 fps or vice versa.