How to Set Hearing Impaired Flag in MKV with FFmpeg

This article provides a quick and direct guide on how to use FFmpeg to set the hearing-impaired flag on audio or subtitle streams inside an MKV (Matroska) container. By using FFmpeg’s disposition metadata mapping, you can flag these streams for media players without needing to re-encode the video or audio tracks.

Setting the Flag on Subtitles

To flag a subtitle stream as hearing-impaired (often used for SDH - Subtitles for the Deaf and Hard-of-hearing), use the -disposition option targeting the subtitle stream index.

The following command sets the hearing-impaired flag on the first subtitle stream (s:0) while copying all video, audio, and subtitle data without re-encoding:

ffmpeg -i input.mkv -c copy -disposition:s:0 hearing_impaired output.mkv

Setting the Flag on Audio

If you have a dedicated audio description stream or an audio track designed for the hearing-impaired, you can flag it in a similar way.

The following command sets the hearing-impaired flag on the first audio stream (a:0):

ffmpeg -i input.mkv -c copy -disposition:a:0 hearing_impaired output.mkv

Setting the Flag on Multiple Streams Simultaneously

If you want to apply the hearing-impaired flag to both the first audio stream and the first subtitle stream at the same time, combine the disposition arguments into a single command:

ffmpeg -i input.mkv -c copy -disposition:a:0 hearing_impaired -disposition:s:0 hearing_impaired output.mkv

Targeting Specific Streams

If your MKV file contains multiple audio or subtitle tracks, you can target specific ones by changing the index number:

• -disposition:s:1 hearing_impaired targets the second subtitle track.
• -disposition:a:2 hearing_impaired targets the third audio track.

Because the -c copy flag is used, this process is extremely fast and preserves the exact quality of your original file.