How-to
Add captions to an MP4
MP4 is the format almost everything ends up in, and it is the format almost every platform wants back. This covers adding captions to one without an editor and without changing anything else about the file.
Three ways captions and MP4 fit together
| Burned in | The text is rendered into the picture during encoding. Plays everywhere, cannot be switched off, and is what social platforms need. |
|---|---|
| Muxed into the container | MP4 can carry a text track alongside the video. Support is patchy, and many players and platforms ignore it entirely. |
| Sidecar SRT | A separate file uploaded next to the video. Well supported by video platforms, ignored by most social feeds. |
Burned in is the option that behaves the same everywhere, which is why it is the default here. You still get the sidecar SRT with every job, so you are not locked out of the other approach.
How to do it
Upload the MP4
Up to 500 MB. MOV, AVI, and MKV work the same way.
Choose the caption language
Pick the original spoken language for straight captions, or another language to translate as well.
Download the captioned MP4
The captions are rendered into the picture and the file is encoded back to MP4, along with SRT and TXT files.
Captions or subtitles?
The words get used interchangeably, but they are not the same thing. Captions are written for viewers who cannot hear the audio and traditionally include speaker changes and relevant sound; subtitles assume you can hear and just need the words. What you get here is the spoken words timed to the video, in the original language or translated. Subtitles vs captions covers where the distinction actually matters.
Things worth checking on the finished file
- Watch it on a phone. Most viewing happens there, and text sized for a desktop preview is often too small.
- Check the bottom edge for collisions with player controls and platform overlays, especially in vertical formats.
- Confirm the audio is untouched. Adding captions re-encodes the picture, not the speech.
- Keep the original file. Burned-in text cannot be cleanly removed afterwards.
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Continue with Google50 free credits. No credit card needed.Frequently asked questions
Will adding captions change my MP4 in other ways?
The picture is re-encoded so the text can be drawn into it, which adds one compression generation. The audio and the length of the video are unchanged.
Can I add captions to a MOV, AVI, or MKV file?
Yes. All four formats are accepted up to 500 MB, and the output is an MP4.
Do I get a caption file separately?
Yes. Every job returns SRT and TXT files in the original language and in the language you selected.
Can I add captions in the same language as the audio?
Yes. Choose the original spoken language and you get captions rather than a translation, which is what accessibility and silent autoplay both need.