Embedded SUBRIP subtitle renders the wrong track: selected stream index is halved (direct play)

[ryanvanderveen]

This issue respects the following points:

• I have discussed this issue in the Jellyfin forum and/or troubleshooting chat before opening this issue.
• This issue is not already reported on GitHub (I've searched it).
• I agree to follow Jellyfin's Code of Conduct.
• This report addresses only a single issue; If you encounter multiple issues, kindly create separate reports for each one.

Describe the bug

When a subtitle track is delivered via the Embed path during direct play, the player selects the wrong track: it renders the track at roughly half the requested server stream index.

On a file with many subtitle tracks this is trivially reproducible and fully deterministic. Selecting English SDH (server stream index 5) shows no subtitles at all, because index 5 maps to 2, and stream 2 is an audio track — so there is nothing to render and the failure is silent (no error, no crash).

ASS/SSA tracks are not affected, because the server burns those in (Restarting playback for subtitle baking) and that path uses the correct index. Only SUBRIP tracks, which take the method Embed path, are mis-mapped. This is what makes the bug confusing in practice: some subtitle tracks work perfectly while others silently do nothing.

Reproduction / evidence

Test file has 18 subtitle tracks at server stream indices 3–20. Each row below is a single selection from the in-player subtitle menu, with the corresponding log line and what actually appeared on screen (verified by screenshot and by grepping the server-extracted subtitle files for the exact rendered line):

Menu entry selected (server index)	Log line	Actually rendered
SDH - English - Hearing Impaired - SUBRIP (5)	Enabling subtitle group 5 via method Embed	nothing (→ index 2 = audio track)
SDH - German - Hearing Impaired - SUBRIP (8)	Enabling subtitle group 8 via method Embed	English sub-script (→ index 4, ASS)
European (SDH) - Spanish - Hearing Impaired - SUBRIP (12)	Enabling subtitle group 12 via method Embed	Arabic (→ index 6, ASS)
Latin American (SDH) - Spanish - Hearing Impaired - SUBRIP (10)	Enabling subtitle group 10 via method Embed	English SDH (→ index 5)

The relation rendered = floor(requested / 2) held for every case. The last row was predicted before testing and confirmed — selecting the Spanish LatAm SDH entry is currently the only way to actually display the English SDH track on this file.

The app resolves the menu entry to the correct server stream index (the Switching subtitles from index X to Y line is always correct); the mis-mapping happens when that index is handed to the player as a track "group".

Possibly related: #5407 (IndexOutOfBoundsException in StreamInfo.getSubtitleDeliveryMethod()) — that may be the same index mishandling in the case where the bad index falls out of range, rather than silently landing on a valid but wrong track.

Media info of the file

Matroska, direct played (play_method = DirectPlay), no transcode. Stream layout as reported by ffprobe:

0  video     h264
1  audio     aac    jpn
2  audio     aac    eng
3  subtitle  ass    eng  Forced          (forced=1)
4  subtitle  ass    eng                  (default=1)
5  subtitle  subrip eng  SDH             (hearing_impaired=1)
6  subtitle  ass    ara  Saudi Arabia
7  subtitle  ass    ger
8  subtitle  subrip ger  SDH             (hearing_impaired=1)
9  subtitle  ass    spa  Latin American
10 subtitle  subrip spa  Latin American (SDH)  (hearing_impaired=1)
11 subtitle  ass    spa  European
12 subtitle  subrip spa  European (SDH)  (hearing_impaired=1)
13 subtitle  ass    fre  European
14 subtitle  subrip fre  European (SDH)  (hearing_impaired=1)
15 subtitle  ass    ita
16 subtitle  subrip ita  SDH             (hearing_impaired=1)
17 subtitle  ass    pol
18 subtitle  ass    por  Brazilian
19 subtitle  subrip por  Brazilian (SDH) (hearing_impaired=1)
20 subtitle  ass    rus
21+ attachment (18 embedded fonts)

Client logs

I/PlaybackControllerHelperKt: Switching subtitles from index 5 to 8
I/PlaybackControllerHelperKt: Enabling subtitle group 8 via method Embed
I/PlaybackControllerHelperKt: Switching subtitles from index 8 to 12
I/PlaybackControllerHelperKt: Enabling subtitle group 12 via method Embed
I/PlaybackControllerHelperKt: Switching subtitles from index 12 to 10
I/PlaybackControllerHelperKt: Enabling subtitle group 10 via method Embed

For contrast, an ASS track selection takes the working path and displays correctly:

I/PlaybackControllerHelperKt: Switching subtitles from index 5 to 6
I/PlaybackControllerHelperKt: Restarting playback for subtitle baking

Application version

0.19.10 (also reproduced identically on 0.18.11)

Where did you install the app from?

Google Play Store

Device information

TCL Google TV (4K)

Android version

Android 14

Jellyfin server version

10.11.11

Other sources

No response