Client floods server with Subtitle requests when subtitle mode is set to Always Play and preferred language is not available

[keriati]

Describe the bug

Description:

With the setting Subtitles > Preferred subtitle language set to any value
and the setting *Subtitles > Subtitle mode set to Always play

when we start a movie that does not have the subtitle available
the client floods the server with requests that all result in 404 errors
(that can result in banning the client IP by crowdsec)

Steps to reproduce:

On Jellyfin Web client click on 👤 icon
Click on Subtitles
Select Preferred subtitle language any language that is not available in a video file
Select Subtitle mode with value Always Play

On Swiftfin play a movie

Observe access logs from Jellyfin server getting flooded with 404 requests.

Example Access log:

{
  "Path": "/Videos/<id>/<number>/Subtitles/21/0/Stream",
  "Status": 404,
  "UserAgent": "VLC/3.0.21 LibVLC/3.0.21",
  "Start": "2025-02-02T22:03:21.814143325Z"
}
{
  "Path": "/Videos/<id>/<number>/Subtitles/21/0/Stream",
  "Status": 404,
  "UserAgent": "VLC/3.0.21 LibVLC/3.0.21",
  "Start": "2025-02-02T22:03:22.012996487Z"
}
{
  "Path": "/Videos/<id>/<number>/Subtitles/21/0/Stream",
  "Status": 404,
  "UserAgent": "VLC/3.0.21 LibVLC/3.0.21",
  "Start": "2025-02-02T22:03:22.132087334Z"
}
{
  "Path": "/Videos/<id>/<number>/Subtitles/22/0/Stream",
  "Status": 404,
  "UserAgent": "VLC/3.0.21 LibVLC/3.0.21",
  "Start": "2025-02-02T22:03:22.281193547Z"
}
{
  "Path": "/Videos/<id>/<number>/Subtitles/22/0/Stream",
  "Status": 404,
  "UserAgent": "VLC/3.0.21 LibVLC/3.0.21",
  "Start": "2025-02-02T22:03:22.456099257Z"
}
{
  "Path": "/Videos/<id>/<number>/Subtitles/22/0/Stream",
  "Status": 404,
  "UserAgent": "VLC/3.0.21 LibVLC/3.0.21",
  "Start": "2025-02-02T22:03:22.625229877Z"
}
{
  "Path": "/Videos/<id>/<number>/Subtitles/22/0/Stream",
  "Status": 404,
  "UserAgent": "VLC/3.0.21 LibVLC/3.0.21",
  "Start": "2025-02-02T22:03:22.776382391Z"
}
{
  "Path": "/Videos/<id>/<number>/Subtitles/22/0/Stream",
  "Status": 404,
  "UserAgent": "VLC/3.0.21 LibVLC/3.0.21",
  "Start": "2025-02-02T22:03:22.956122846Z"
}
{
  "Path": "/Videos/<id>/<number>/Subtitles/22/0/Stream",
  "Status": 404,
  "UserAgent": "VLC/3.0.21 LibVLC/3.0.21",
  "Start": "2025-02-02T22:03:23.146656708Z"
}
{
  "Path": "/Videos/<id>/<number>/Subtitles/23/0/Stream",
  "Status": 404,
  "UserAgent": "VLC/3.0.21 LibVLC/3.0.21",
  "Start": "2025-02-02T22:03:23.292953191Z"
}

Application version

1.2

Where did you install the app from?

App Store

Device information

iPhone / iPad

OS version

18.3

Jellyfin server version

10.10.5