Subtitle sync issues with H.265 (HEVC) videos across multiple clients on RP5 Server

[PerfectJam]

Hi everyone,

I'm encountering persistent subtitle synchronization issues when playing H.265 (HEVC) videos with embedded subtitles using Jellyfin. The subtitles are out of sync, often in advance. This happens both for local and remote (WebDAV/seedbox) playback, and only with H.265 videos, on H.264 videos everything is ok.

My setup:

• Server: Jellyfin in Docker on a Raspberry Pi 5 (8GB RAM)
  
• Storage: 
  

- when using in local : local SSD
- when using remote : WebDAV rclone mount (see code below)

Clients:

• LG WebOS TV (OLED55B8PLA) using the official Jellyfin app
  
• Fairphone 5 (Android) using the official Jellyfin app
  

Observations:

• Subtitles are perfectly in sync when played in VLC (on both PC and mobile),  suggesting it may be a client-side rendering issue in Jellyfi ?
  
• H.264 videos play perfectly with subtitles.
  
• The issue persists even during local playback, so it doesn't seem to be bandwidth-related.
  
• I’ve disabled "Allow subtitle extraction on the fly" in playback settings.
  
• Hardware transcoding (VAAPI) is enabled on the server.
  

I added the last log
Questions:

1. Is this a known issue with Jellyfin’s internal player handling subtitles on H.265 videos with a Raspberry Pi ?
   
2. Is there any way to force correct subtitle syncing without re-encoding my entire library ?
   

Thank you for any help!

WebDAV rclone code :

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Spoiler

Code:

rclone mount seedbox:/Seedbox/ /home/pi/media/seedbox/ \  
--vfs-cache-mode full \  
--vfs-cache-max-size 10G \  
--vfs-cache-max-age 5m \  
--cache-dir=/mnt/ssd/rclone_cache \  
--buffer-size 64M \  
--dir-cache-time 72h \  
--poll-interval 15s \  
--timeout 1m \  
--daemon \  
--allow-other