Subtitles dropped, even when transcoding from MKV to MKV

[mcandre]

Avidemux could improve how it manages subtitle tracks. When I try to append one MKV file to another MKV, the subtitle tracks are missing from the output MKV.

[eumagga0x2a]

Not that support for soft subtitles is deemed insignificant or is not wanted, but https://avidemux.org/smif/index.php?topic=19128.0 still applies.