Hardcoded subtitles, unlike soft or embedded subtitles, can not be turned on or off, as they are burnt in to the video file itself. MKVs are multi-media containers that may contain several subtitle tracks that can be turned on or off as needed. Hardcoding one set of subtitles on to your MKV requires an MKV conversion program to re-encode your entire file. Fortunately, there are several free, open-source programs available for download, like HandBrake and TEncoder that support MKV input and output with options for hardcoded subtitles. Other programs with free-trial options include AVC's Any Video Converter.
Hardcoding Subtitles With HandBrake
Click the "Source" button in the top-left of the screen and select "Video File" to open a pop-up search window of your computer's contents. Browse to your input MKV file, highlight its icon and click "Open" to load it in HandBrake.
Press the "Browse" button to the right of the Destination field near the top of the screen and choose a save location for your output MKV.
Click the "Container" button in the Output Settings field and select "MKV."
Click the "Subtitles" tab in the middle of the screen and press the "Add External Subtitle" button to open another pop-up search window. Navigate to your input subtitle file, highlight its icon and click "Open."
Press the "Burned In" button next to your input subtitle. Note that SRT subtitle files cannot be burnt into MKV video; however, you can use standard MKV SSA subtitles and DVD VobSubs.
Click the "Start" button at the top of the screen to begin re-encoding your MKV with hardcoded subtitles.
Hardcoding Subtitles Using TEncoder
Launch your Internet browser and visit the TEncoder download page. Click the "Download" button and wait for the ".exe" program file to finish downloading to your computer. Double-click its icon to initiate the installation process and choose a location on your hard drive to save the program to. Follow the on-screen instructions, agree to the licensing terms and launch TEncoder.
Open a Windows Explorer screen and locate your input MKV file. Leave this window open. Open a second Windows Explorer screen and locate your input subtitle file. Rename it so the file has the exact same name as your MKV and drag and drop it into the same folder as your MKV. For example, if your MKV is called "mkv_video.mkv," name your subtitle "mkv_video," but keep its original file extension.
Click the "Add Folder" button in TEncoder's main window and highlight the folder containing your input MKV and subtitle files. Click "Open" so both files load in TEncoder.
Press the "Options" button below the File list and click "Video Options." Click the "Video Codec" drop-down menu and select "Copy" to retain the same codec as your original MKV. You may also choose to convert your MKV codec to H.264 or Xvid, as these are both compatible, high-quality MKV codecs.
Click the "Other Options" tab and select "Enable Subtitles." Click the "Do Two Passes" box for best quality and click "Encode."
Hardcoding Subtitles Using Any Video Converter
Navigate to Any Video Converter's home page in your Web browser and click the "Download" button on the right side of the screen for your free trial version. Double-click the ".exe" program file when your download has finished and follow the program's instructions to install the software on your computer. Agree to the licensing terms and launch Any Video Converter.
Browse your computer in a new Windows Explorer screen and locate your input MKV file. Open a second Windows Explorer screen, locate your subtitle file and rename it so it has the exact same file name as your MKV; however, keep its original file extension. For instance, if your MKV is called "feature_video.mkv," name your subtitle file "feature_video" plus its file extension. Drag and drop your renamed subtitle file into your MKV's folder.
Press the "Add Video" button in the top-left corner of Any Video Converter. Browse the pop-up search screen and double-click your MKV's icon to load it in the program's window.
Click the "Output Profile" button in the upper-right corner of the screen, select "Video Files" and choose an MKV output option.
Click the "Audio Options" drop-down box on the right-hand side of Any Video Converter, click the "Subtitle" button and choose your input subtitle.
Press the "Options" button in Any Video Converter's main screen and click the "Subtitles" tab. Click the "Default Subtitle Encoding" button and choose "UTF-8." Change the font, size or position of your subtitles as needed by using the slidebars and drop-down boxes. Click "OK" to save your changes and exit back to the main screen.
Click the "Convert" button at the top of the screen to begin encoding your subtitle to your MKV video.
Re-encoding MKV files may take up to several hours to complete, depending on the file size and your computer's processing speed.