Add selectable subtitle tracks to an MKV on Mac

Give the two English tracks different jobs

Imagine a Dutch short film in which a cyclist waits outside a flat. A buzzer sounds off camera and the door opens. An English dialogue subtitle can stay silent at the buzzer; an English caption for deaf and hard-of-hearing viewers might read “[door buzzer]”. Both tracks should translate the spoken invitation that follows. That one scene gives your distributor a quick way to tell the tracks apart.

Ask which players the distributor supports and whether they accept selectable text in an MKV. If they require open captions burned into the picture, this file will not meet the brief. Confirm permission to distribute this cut, the dialogue translation and the accessibility captions to the intended audience. Keep your editable master and approved text files separately.

Prepare one SRT for each audience

Work from a supported review movie with the same first frame, duration and audio as the delivery cut. On an Apple Silicon Mac, use Polyglot to transcribe the dialogue locally after model setup, or open a matching SRT and attach the review movie. Review the English translation with someone fluent in both languages. Export the approved dialogue track before making a separate working copy for captions.

The buzzer needs its own cue because nobody speaks over it. In a separate SRT editor, add a numbered cue to the caption copy with the buzzer’s start and end times, then renumber the following cues in sequence. Open that SRT as a separate Polyglot project with the review movie. Check that the label starts with the sound, clears before the invitation and appears only in the caption copy. Verify a line near the end credits too: an extra distributor ident at the start or an edit in the middle can leave a correctly translated file on the wrong clock.

Package the files without losing track identity

Polyglot exports the SRT files. Use MKVToolNix for the separate packaging step. In its multiplexer, add the final movie as a source and add both SRT files as additional sources, not as appended segments. Inspect the input track list first: retain the approved picture and audio, and deselect any obsolete subtitle draft. Choose a new output filename so the master remains intact.

Set the language to English for both subtitle tracks. Give them different track names, for example “English dialogue” and “English SDH”. Set the hearing-impaired flag on the SDH track. If the brief calls for the dialogue track to be the ordinary English choice, mark it default and clear default on the SDH track. Leave forced display off for both complete tracks. Default helps a player choose among eligible tracks; a viewer’s language or accessibility preferences can change that choice. A forced flag is not a stronger default.

Check the copy the distributor will receive

Move only the new MKV into an empty folder, leaving the SRTs behind. Open that copy in the intended player. With English dialogue selected, watch the buzzer and the invitation; repeat with English SDH. The buzzer label should appear only in SDH, while the translated invitation should appear in both. Switch subtitles off: if the invitation is still visible, check whether the picture already contains text or the player is loading another subtitle source.

Reopen the MKV and check the startup selection under the recipient’s normal language settings. Record the player, preferences and the two menu entries separately from what actually appeared. If both menu entries say only “English”, inspect the names stored in the MKV before changing the SRTs: a player may omit track names from its menu. If the sound label appears in both tracks, inspect the packaged inputs. Changing a default flag cannot fix two copies of the same text.

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