SRT subtitles force software decoding on iOS

[mssssman 1]

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 May 29 by mssssman
Correcting numbering

[Luke 42557]

Hi, so these are internal subs?

[mssssman 1]

 

On 5/31/2026 at 2:47 PM, Luke said:

Hi, so these are internal subs?

They are external, I can test internal subtitles but I have not if that's necessary

[mssssman 1]

On 5/31/2026 at 2:47 PM, Luke said:

Hi, so these are internal subs?

So I did try internal subtitles and changed my current srt subtitles into mov_text and muxed them into the video and that fixed the software decoding issue but I think this should still be looked into because your subtitle downloader dose the default behavior that caused the software decoding on my phone

[visproduction 361]

I wonder if the internal subs trigger transcoding just because to handle the resolution setting plus internal subs goes over the limit, even though you are not planning to use the internal subs, they might be noticed anyway.  Can you see if removing an internal embedded subs helps? This is just a guess.

 

[Luke 42557]

Hi, we are looking into this. Thanks.

[mssssman 1]

On 6/11/2026 at 5:27 PM, Luke said:

Hi, we are looking into this. Thanks.

Thanks!