SRT subtitles force software decoding on iOS

[mssssman 0]

Device: iPhone 16
Emby App Version: 2.2.53
Emby Server Version: 4.9.5.0 (running on TrueNAS Community Edition)

Issue: Using SRT subtitles on ios forces software decoding

Server Configuration
Transcoding is fully disabled on the server. I encode multiple resolution versions for each video so i don't have to transcode on the fly.

Steps to Reproduce
1. Play any compatible video where hardware decoding works correctly
2. Enable SRT subtitles during playback
3. The app switches to software decoding

Expected Behavior
SRT subtitles are plain text and should be rendered as a client-side overlay without affecting the decoding pipeline and hardware decoding should remain active.

Actual Behaviour
Enabling SRT subtitles appears to trigger subtitle burn-in forcing software decode which causes significant device heat and rapid battery drain.

Evidence
The attached screen recording demonstrates the issue. I played the video at 2x speed to confirm hardware decoding is active (no dropped frames). After subtitles are turned on the player switches to software decoding clearly seen by how laggy it is.

Video File Specs
Encoded with: HandBrake 1.11.0
Video codec: AV1 (Main Profile @ Level 5.0)
Resolution: 3840 × 1606
Frame rate: 23.976 fps (CFR)
Bit rate: 12.5 Mb/s
Bit depth: 10-bit
Color: YUV 4:2:0, BT.2020, PQ transfer (HDR10)
HDR: Dolby Vision (Profile 10, BL+RPU) with HDR10 compatibility
Audio: AAC-LC, Stereo, 160 kb/s CBR

Subtitle File
Format: SRT (SubRip Text)
Encoding: UTF-8 with BOM

Additional Notes

1: This only happens on the ios app, Playback on chrome and my firestick 4K Gen 2 plays the video back with subtitles fine with no issues.

2: The subtitles are external SRT files downloaded directly through Emby's built-in subtitle downloader. The video file itself has no embedded subtitles.

3: Jellyfin handles SRT subtitles on the same file correctly they are rendered as a client-side overlay with no impact on decoding which suggests the issue is specific to how the Emby ios app handles subtitle rendering.

Edited 3 hours ago by mssssman
Correcting numbering