In this tutorial I will describe you how to add subtitles into a matroska .mkv file. The software I will use is mkvmerge GUI which is part of the MKVToolnix package. Both programs are available for Windows and Linux. Here I will use the Windows version. Since I suppose you already have the video file along with its .srt subtitles somewhere in your hard disk download the latest version of MKVToolnix, install it and let's get started!
This is the main window of mkvmerge GUI.
Press the Add button and first load your .mkv file. Press Add once more and load your .srt subtitles file.
In General track options under Language select the subtitles language. You may add multiple .srt subtitles and choose which one you want to be the default. Moreover set the output filename.
Now you are ready. Just press the Start Muxing butting. In a few minutes the new .mkv file will be ready.
Note: If you get a message mkvmerge failed with a return code of 2. Could not write the output file make sure the output path is correct and you have write priviledges on it.
Now just open the video with any .mkv compatible player such as VLC. It was pretty easy to mux your subs, wasn't it?