Free online MKS to SRT converter

Media players, video editors, and upload systems often accept external .srt subtitles but cannot use an .mks container. Converting is also necessary when subtitle text must be edited, translated, or distributed as a separate small text file.

What the MKS format is

.mks is a filename extension convention for a Matroska container that normally holds subtitle tracks without video or audio. It is related to .mkv, but the extension does not identify the subtitle format stored inside.

An MKS file can contain one or more tracks in different languages and codecs. Text tracks may contain SubRip-compatible UTF-8 text, ASS, SSA, or WebVTT; bitmap tracks may contain Blu-ray PGS or DVD VobSub subtitles. Matroska users, remuxers, archivists, and people extracting tracks from MKV files commonly use MKS files.

Check the track codec before conversion. A Matroska file containing SubRip text may only need extraction, while PGS and VobSub contain subtitle images and need OCR to become SRT text.

What the SRT format is

SRT is a plain-text subtitle format with numbered cues, start and end timestamps, and dialogue lines. A cue timestamp uses the form 00:01:23,456 --> 00:01:26,789.

SRT is widely supported by media players, televisions, subtitle editors, video editors, and subtitle-upload services. It is small, editable in text editors, and normally saved as UTF-8.

SRT cannot preserve ASS or SSA fonts, colors, screen positions, drawing commands, karaoke effects, or animations. It also cannot directly store PGS or VobSub bitmap captions.

Convert text-based MKS files

For a text-based MKS file, upload the file to the converter on 101convert.com, choose SRT as the output format, and download the result. The conversion can be performed free without installing software.

For local conversion, first inspect the subtitle streams with FFmpeg:

ffprobe -v error -select_streams s -show_entries stream=index,codec_name:stream_tags=language,title -of default=noprint_wrappers=1 input.mks

If the codec is subrip or Matroska identifies it as S_TEXT/UTF8, the track already contains SRT-compatible text. Extract it with MKVToolNix:

mkvmerge -i input.mks

Use the displayed Matroska track ID in:

mkvextract tracks input.mks 0:output.srt

Replace 0 with the required track ID. An MKS file can contain multiple subtitle tracks, so extract each required language or forced-subtitle track separately.

For ASS, SSA, and supported WebVTT text tracks, FFmpeg can create SRT output:

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

Change 0:s:0 to 0:s:1, 0:s:2, and so on to select another subtitle stream. FFmpeg's subtitle-stream ordinal in -map is not necessarily the same as the track ID shown by mkvmerge.

Subtitle Edit is useful when an extracted ASS or SSA file needs review before export. Open the extracted file, then use File → Save as and select SubRip (*.srt).

Convert bitmap subtitles with OCR

Codecs such as hdmv_pgs_subtitle and dvd_subtitle contain rendered subtitle images, not text. FFmpeg cannot directly convert those images into accurate SRT dialogue.

Extract the bitmap track with mkvextract, open it in Subtitle Edit, run its OCR function, correct the recognized text, then save through File → Save as as SubRip (*.srt). Stylized fonts, low contrast, overlapping dialogue, signs, and non-Latin scripts can cause OCR errors.

Compatibility checks

ASS and SSA conversion retains dialogue and timing but discards styling and positioning. OCR output can contain spelling, punctuation, character-recognition, and line-break errors; proofread it while comparing it with the video.

Matroska metadata such as language, title, default, and forced-track flags is not stored in a normal SRT file. Use descriptive filenames such as movie.en.srt and movie.en.forced.srt.

Test the result in the intended player and check timing, cue order, line breaks, and accented characters. Save as UTF-8; if an older television displays incorrect characters, try UTF-8 with BOM or the encoding required by that device.