Free online MKS to VTT converter

What the MKS format is

MKS is a Matroska container used mainly for subtitle-only files. It is often produced by MKVToolNix when a subtitle track is extracted from an MKV video, and it can contain formats such as SubRip (SRT), ASS/SSA, or bitmap subtitles such as PGS.

You may encounter MKS files alongside downloaded video releases, archival MKV files, or subtitle tracks exported with MKVToolNix GUI → Multiplexer. The filename does not identify the subtitle encoding by itself; the stream inside the container determines whether conversion to VTT is possible.

What the VTT format is

WebVTT, normally saved with the .vtt extension, is a UTF-8 caption and subtitle format designed for HTML5 video. A VTT file starts with WEBVTT and stores timed cues such as:

WEBVTT

00:00:02.000 --> 00:00:05.500
Example subtitle

VTT supports cue positioning, alignment, voice labels, and limited styling. It is suitable for websites, browser players, accessibility captions, and platforms that accept WebVTT but reject MKV-based subtitle containers.

How to convert MKS to VTT

Using 101convert.com

1. Open the MKS-to-VTT converter on 101convert.com.
2. Upload the .mks file and select VTT as the output format.
3. Start the conversion, then download the resulting .vtt file.
4. Open the result in a subtitle editor or browser player and check cue timing, characters, and line breaks.

This option requires no software installation. It works best when the MKS contains a text subtitle stream rather than an image-based stream.

Using FFmpeg

FFmpeg can convert a compatible text subtitle stream directly:

ffmpeg -i input.mks -map 0:s:0 -c:s webvtt output.vtt

-map 0:s:0 selects the first subtitle stream. If the file contains several tracks, inspect them first:

ffprobe input.mks

Replace the stream selection with -map 0:s:1, for example, to convert the second subtitle stream. To preserve the original subtitle language or choose a different track, identify the stream metadata in the FFprobe output.

Using a subtitle editor

Subtitle Edit can open many Matroska subtitle files and export supported text tracks through File → Save as. Open the MKS file, select WebVTT as the output type, verify the encoding is UTF-8, and save it with a .vtt extension. Menu names and MKS support can vary by application version.

Quality and compatibility limits

A text-based MKS track, such as SRT or ASS, can normally be converted to VTT. ASS-specific typography, advanced positioning, karaoke effects, and some styling may be simplified or discarded because VTT does not implement the full ASS feature set.

Bitmap subtitles such as PGS cannot be converted into editable VTT cues by changing containers. They require OCR, manual transcription, or a subtitle editor that can recognize subtitle images; OCR output must be reviewed for character and timing errors.

Check the first line of the result for WEBVTT, confirm that timestamps use the HH:MM:SS.mmm --> HH:MM:SS.mmm form, and make sure the file is saved as UTF-8. Some browser players reject malformed timestamps, unsupported styling, or cue times that extend beyond the associated video.