I want to remux a mkv file into mp4. I used the following command.

ffmpeg -i "input.mkv" -c:v copy -c:a copy -map 0:0 -map 0:1 -map 0:2 -map 0:3 -c:s mov_text "output.mp4"

Problem: The subtitles in the output.mp4 file are way too small.

Also, the subtitles of the mp4 file are unaffected when I try to make them bigger from vlc preferences. I can turn them on/off but I think they are somewhat hardcoded. I had to rencode subtitles while remuxing as otherwise it was showing error. Also, I'm using the latest version of mmpeg.

input.mkv :

output.mp4 :

input.mkv has the following streams,codecs :

I searched a lot, but couldn't find a way to make mov_text subtitles bigger. How can I make them bigger?

Or Please suggest any other way to retain the subtitles while remuxing from mkv to mp4.

2 Answers 2


I consider subtitle text rendering is part of the player feature. If you are using VLC, may this link, https://wiki.videolan.org/VLC_HowTo/Adjust_subtitle_font_settings/, help?

I had tried on a mkv to mp4 video, before enter image description here

After, I changed the VLC subtitle font size to larger, exited the program and replayed it again, i got enter image description here

  • I already tried to change font size, appearance from vlc preferences, as I mentioned in the post. But it did not have any affect on the subtitiles. Oct 18, 2020 at 13:42
  • i updated my answer with screen-capture
    – xer-rex
    Oct 19, 2020 at 8:03
  • Every other text becomes large except the subtitles.ScreenShot , Also you can notice that the subtitles are not hardcoded. Still their size is unaffected by changes in vlc preferences. Oct 20, 2020 at 7:29

I was having a similar issue and realised it was because the subtitles contained style information that VLC was only rendering in the output file, not the input file. Have you checked if the SSA subtitle file contains some style specifications like font size? To copy the contents of the SSA without the style information you can use

ffmpeg -i input.mkv -map 0:s -c:s text output.srt

and then mux those into the mp4.

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge you have read our privacy policy.

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