Changing font size for transcoded subtitles

[FeralHogEnjoyer]

Hi, first I want to say thank you to all those who work on jellyfin and make it so great.

The feature I'm requesting is the ability to change the font size when subtitles are burned into a transcode. I really enjoy burning in subtitles when transcoding is necessary because I find that it often goes out of sync otherwise. The only problem is that the font size is far too large and takes up half the screen when being burned in. I suggest a way to change the font size. Perhaps the settings for font size from the client should be sent to the server so ffmpeg can use that info and set a specific font size.

Thanks for reading.

[Rastin]

I don't think the developers visit this site much but I'm sure they they appreciate your thanks. I believe most people who respond are mostly other users like yourself. Since i don't know muck about sub's my self i got you a response from chat gpt below. Hopes it helps some.



That’s a very reasonable feature request, and you’ve clearly described the use case well 👍

In Jellyfin, burned-in subtitles are rendered server-side during transcoding using FFmpeg. When subtitles are burned in, they’re no longer controlled by the client — they become part of the video stream itself. That’s why client-side font settings (size, color, position, etc.) don’t currently affect burned-in subtitles.

Why the font is so large

When FFmpeg burns subtitles:

It either uses the styling embedded in the subtitle file (e.g., ASS/SSA styling), or

Falls back to default styling if it’s something like SRT

For SRT especially, the default font size can scale aggressively depending on video resolution, which is why it can end up taking half the screen.

Is your idea technically feasible?

Yes — absolutely.

FFmpeg supports:

force_style (for ASS subtitles)

Font size overrides

Custom subtitle filters with style parameters

For example, FFmpeg’s subtitles filter allows something like:

-vf "subtitles=subtitle.srt:force_style='FontSize=18'"

So in theory, Jellyfin could:

Pass client subtitle settings (like font size) to the server

Include those settings in the FFmpeg subtitle filter during transcode

Burn subtitles with the adjusted size

Why it’s not currently available

In Jellyfin’s current architecture:

Client subtitle appearance settings are client-side only

Burned-in subtitles are generated entirely on the server

There’s no setting in the UI to control FFmpeg subtitle styling during transcode

So your suggestion would require:

A new server-side setting (or per-user setting)

Passing that preference into the FFmpeg transcode command

Possibly adding per-session override logic

Workarounds You Can Use Now
1. Convert SRT to ASS with custom styling

You can:

Convert your .srt to .ass

Define a smaller font size in the ASS style

Jellyfin will respect that when burning in

You can do this with:

Subtitle Edit (GUI)

Aegisub

Or FFmpeg conversion

This gives you full control over:

Font size

Position

Outline

Margins

2. Reduce Burn-In by Fixing Sync

Since you mentioned you burn subtitles because of sync issues — sometimes this can be solved by:

Converting subtitles to UTF-8

Remuxing the file instead of transcoding

Ensuring subtitle timebase matches video

Sometimes out-of-sync subtitles are caused by container issues rather than needing burn-in.

If You Want to Submit This Properly

You can submit or search for an existing feature request on the official GitHub:

Jellyfin GitHub

A good feature request would include:

Why burned-in subs are needed (sync reliability)

Accessibility concerns (screen coverage)

Reference to FFmpeg’s force_style

Suggest per-user or per-session control