I have a good quality MKV file that has several subtitle options. I want to add an additional subtitle file to the list. I'm using OSX.

Some search online led me to use video converters, and basically re-encode the movie into a new file. That seems really overkill to me. Plus I may loose the previous subtitles, and some image quality along the way.


Removing subtitles:

mkvmerge -o output.mkv input.mkv -S # remove all subtitle tracks
mkvmerge -o output.mkv input.mkv -s 3,4 # remove tracks 3 and 4
mkvmerge -o output.mkv input.mkv -s '!3' # remove all subtitle tracks except 3
mkvmerge -i input.mkv # show track numbers

Adding subtitles:

mkvmerge -o output.mkv input.mkv subs.srt
mkvmerge -o output.mkv input.mkv --language 0:ger --track-name 0:German subs.srt

Extracting subtitles:

mkvextract tracks input.mkv 3:subs.srt
for f in *.mkv; do
  sub=$(mkvmerge -i "$f" | awk '$4=="subtitles"{print;exit}')
  [[ $sub ]] || continue
  [[ $sub =~ S_TEXT/ASS ]] && ext=ass || ext=srt
  track=$(awk -F '[ :]' '{print $3}' <<< "$sub")
  mkvextract tracks "$f" "$track:${f%mkv}$ext"

mkvmerge and mkvextract can be installed with brew install mkvtoolnix.

  • 2
    MKVMerge GUI is already available on Mac OS X, but nevertheless, it's a good how to for console fans. – Bora Jun 18 '13 at 23:35
  • Note that the above commands for adding subtitles also set the subtitles as “enabled by default” when playing the file. (This flag can be confirmed using the MKVMerge GUI.) To avoid this, use --default-track '0:0'. – Mathias Bynens May 5 '16 at 20:45
  • The -s 3,4 now does the opposite, it preserves the tracks 3 and 4. $ mkvmerge.exe --version mkvmerge v43.0.0 ('The Quartermaster') 64-bit – Det Feb 20 '20 at 15:47
  • Actually looks like it's been that way all this time superuser.com/posts/98401/revisions . Would've been weird to break default functionality. – Det Feb 20 '20 at 15:57
  • With mkvmerge the -S option doesn't work unless it comes before the filenames, at least on v31.0.0. – seisatsu Jul 9 '20 at 15:54

There are two basic ways of showing subtitles. You can encode the pixels into the video itself. This is called "hardsubbing". The advantage here is the simplicity for the video player, it's just a video stream. The disadvantages are that you had to reencode the video, which takes time, and has some fidelity loss. If you get a better translation, well, it's pixels in the video. And you can only have one language.

What is somewhat better is "softsubbing", which is to have a text file someplace, separate from the video stream. There are many different formats of subtitle files, but at their base they all have "text, start what time, remove what time" at their core. Some have additional features like colors and orientation on the screen. The advantage to this is you can have multiple languages (think of a DVD, you have multiple languages available) and you can fix typos and such in the file. And if you don't need subtitles, well you just turn them off.

Softsubs can either be separate files - most players will automagically look for subtitles with the same name (different extension) as the main video. Or certain container file formats (like MKV) can have them embedded inside. Check out MKVtoolnix (there is a mac port) for MKV file tools. This should let you embed softsubs without reencoding.

Note that not all players can support all formats. My experience is that XBMC has issues with SSA files, but the much simpler SRT files are fine. VLC will play anything, if it's supported on your platform.

  • 1
    Good answer, though it should be noted that some soft-subtitles -- especially DVD subtitles -- are bitmap-based, rather than text-based. The main effect of which is to make them almost impossible to edit -_- – evilsoup Jun 18 '13 at 16:17
  • 1
    Yep, IDX+SUB VOBsub, where IDX is a text file but SUB contains bitmaps. – Karan Jun 18 '13 at 19:20
  • changed link to the direct download page. – Bora Jun 18 '13 at 23:38

I realize this is an old question and user495470’s answer has been accepted as of 2013, but since part of the question is about adding subtitles to files, I wanted to add this new addition.

Basically, I needed to merge dozens of .ass subtitles into similarly named MKV files, so doing this one command at a time was not cutting it. So I whipped up this simple Bash script that will search the current directory it’s run from for .ass files and then merge them as expected.

find -E . -maxdepth 1 -type f -iregex '.*\.(ASS|SRT)$' |\
  while read FILEPATH
    DIRNAME=$(dirname "${FILEPATH}");
    BASENAME=$(basename "${FILEPATH}");
    mkvmerge -o "/Users/jake/${FILENAME}"-NEW.mkv "${FILENAME}".mp4 --language 0:eng --track-name 0:English "${FILENAME}"."${EXTENSION}"

Of course, this simple script assumes that the subtitles are English and merges them as such, but that can be manually adjusted per usage need; the big issue of automatically merging the subtitles with the MKV is solved by a simple script like this.

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