For permanent text overlays (like titles or watermarks), online editors like Canva allow you to upload MKV files, add text layers, and export them. 3. Quick Video Editing

Right-click the file and select to add subsequent parts.

You can use VEED.io or MKVToolNix to "mux" an SRT subtitle file into your MKV container.

If you want to add a text-based chapter list, you can import .xml or .txt chapter files directly in the "Output" tab of MKVToolNix .

If your goal is to "put together" text with a video (such as subtitles or titles):

For basic editing (trimming or joining) of 1080p MKVs, you can use: Add Text To Video Online For Free - Canva