Subtitle tracks missing metadata

[mpissarello]

FastFlix Version: v5.12.4

Operating System: Ubuntu 24.04

Describe the bug
Transcoding a video preserving subtitles tracks removes the titles from the tracks.
The ffmpeg command generated is missing "metadata" parameters, like those found in audio tracks, for example:

-map 0:10 -c:3 copy -disposition:3 default+forced -metadata:s:3 language='ita' -metadata:s:3 title="Italiano" -metadata:s:3 handler="Italiano"

Furthermore, it would be useful to have in the "Subtitles" tab the ability to edit the titles of the subtitle tracks, as is already possible for audio tracks.

To Reproduce
. open a video with subtitles tracks
. select subtitles to preserve
. encode

Screenshots
MKVToolNix GUI screenshot of the source file:

MKVToolNix GUI screenshot of the transcoded file:

Logs
FastFlix generated ffmpeg command:

"/home/user/ffmpeg" -y \
-i "/home/user/original.mkv" \
-metadata title="My Video" -max_muxing_queue_size 1024 \
-map 0:0 -c:v libx265 -pix_fmt yuv420p10le -metadata:s:v:0 title="My Video" -x265-params "[various params]" -crf:v 20 -preset:v slow -map_metadata -1 -map_chapters 0 \
-map 0:5 -metadata:s:1 title="Italiano" -metadata:s:1 handler="Italiano" -metadata:s:1 language=ita -c:1 aac -b:1 384k -filter:1 "aformat=channel_layouts=stereo" -disposition:1 default+forced \
-map 0:6 -metadata:s:2 title="日本語" -metadata:s:2 handler="日本語" -metadata:s:2 language=jpn -c:2 aac -b:2 384k -filter:2 "aformat=channel_layouts=stereo" -disposition:2 0 \
-map 0:10 -c:3 copy -disposition:3 default+forced -metadata:s:3 language='ita' \
-map 0:8 -c:4 copy -disposition:4 0 -metadata:s:4 language='ita' \
-map 0:9 -c:5 copy -disposition:5 0 -metadata:s:5 language='ita' \
"/home/user/transcoded.mkv"