ffmpeg mov_text subtitle too small when converting mkv to mp4

Question

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.

Answer 1

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

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

Answer 2

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.