Super User is a question and answer site for computer enthusiasts and power users. It's 100% free, no registration required.

Sign up
Here's how it works:
  1. Anybody can ask a question
  2. Anybody can answer
  3. The best answers are voted up and rise to the top

I am trying to embed subtitles in an MP4 contrainer using ffmpeg.

I am using the following command:

ffmpeg -i input.MOV -i -map 0 -map 1 -c copy -c:s mov_text output.MOV

I would like the subtitles to be encoded as tx3g as opposed to text for compatibility with my Video Streamer (Wowza).

Is there any way to change the subtitles encoder?


share|improve this question
To my knowledge standard MOV doesn't support any other subtitle codec. You can of course use any other encoder, but it might not work. – slhck Feb 11 '13 at 16:47
I am flexible on the output type, it be can a mp4 or m4v if that makes it possible. Does it? – Yuval Cohen Feb 12 '13 at 14:55
MP4 (m4v is just another extension) is mostly the same as MOV—actually it heavily builds on MOV, and supports the same video/audio/subtitle formats. You might be able to force another subtitle codec with tools other than FFmpeg, e.g. MP4Box, but I'm not sure, as I've never tried that before. I'll look into that a little later. – slhck Feb 12 '13 at 14:58
up vote 3 down vote accepted

I have to admit I didn't know what the FourCC tx3g really stood for. The FFmpeg codec mov_text and tx3g are the same thing: MPEG-4 Part 17 (Timed Text).

The only thing that FFmpeg does not support is custom styling for the text it embeds. If you look at the source code you'll find that they apply a default style:

For now, we'll use a fixed default style. When we add styling support, this will be generated from the ASS style.

That being said, the free and cross-platform MP4Box should be able to add these subtitles to MP4 files, as you requested. Even with styling. How you add them to the file depends on how they're encoded in the first place. From its documentation:

There is no official textual representation of a text stream. Moreover, the specification relies on IsoMedia knowledge for most structure descriptions. In order to help authoring text streams, an XML format has been developed in GPAC, called TTXT for timed-text – the extension used being .ttxt.

To create a TTXT file, you can do the following:

Find an SRT or SUB subtitle file, and run MP4Box -ttxt This will convert the subtitles in TTXT format.

MP4Box should then be able to add the subtitle stream to an existing MP4 file like so:

MP4Box -add input.mp4 -add subtitles.ttxt output.mp4

It's important that you convert the subtitle files to TTXT before. If they're still SUB or SRT-encoded, MP4Box will simply lay them out with default options:

When importing SRT or SUB files, MP4Box will choose default layout options to make the subtitle appear at the bottom of the video.

share|improve this answer

Your Answer


By posting your answer, you agree to the privacy policy and terms of service.

Not the answer you're looking for? Browse other questions tagged or ask your own question.