"Ambience mode" & ASS/SSA render incorrect

[tomoro02]

Describe the bug
Enabling "Ambience mode" causes ASS/SSA subtitles to render incorrectly. When this mode is active, the subtitles appear stretched and misplaced (they extend beyond their intended boundaries/positioning), making them look different from how they appear with the mode disabled. This issue persists even when adjusting related subtitle settings.

To Reproduce

1. Open a video file containing ASS/SSA subtitles in mpvRx.
2. ​Enable "Ambience mode" in the settings.
3. ​Observe that the subtitles become stretched and lose their correct positioning.
4. ​Disable "Ambience mode" and observe that the subtitles render correctly.

Expected behavior
Subtitles (specifically ASS/SSA) should maintain their original scale and relative positioning regardless of whether "Ambience mode" is enabled or disabled.

Screenshots/Logs

Device Info (please complete the following information):

• App version: 1.4.1-final (53fe4df)
• Android version: 16 (36)
• Device brand: samsung
• Device manufacturer: samsung
• Device model: SM-S921B (e1s)
• MPV version: v0.41.0
• ffmpeg version: 7fc335cb27
• libplacebo version: v7.364.0 (v7.360.0-34-gd5ef02c7)

Additional context
The issue persists despite toggling the following settings:
​

• ​"Scale by window" (Scale subtitles by window size and use video margins).
• ​"Blend subtitles with video" (When ambient mode is on, draw subtitles with the video instead of over the ambient area).

[tomoro02]

Update/Additional context:
I have discovered that this issue is specifically related to the "gpu-next" video output backend.

• When "gpu-next" is disabled, the subtitles render correctly regardless of whether "Ambience mode" is enabled or disabled.
• This suggests a potential compatibility issue between the "gpu-next" shader pipeline and the overlay positioning for ASS/SSA subtitles when "Ambience mode" adds extra margins/borders to the video frame.

[Muzart-arc]

Turn off the Blend subtitles with video option

[tomoro02]

If I disable this option, the subtitles are stretched beyond the video area, even when I don't use gpu-next.
When I use gpu-next, regardless of the settings of the "Blend subtitles with video" option, the subtitles are displayed incorrectly (they are stretched).

Currently, the only way to display subtitles correctly and have "Ambience mode" is:

• disable gpu-next;
• enable "Blend subtitles with video".

[Riteshp2001]

If I disable this option, the subtitles are stretched beyond the video area, even when I don't use gpu-next. When I use gpu-next, regardless of the settings of the "Blend subtitles with video" option, the subtitles are displayed incorrectly (they are stretched).

Currently, the only way to display subtitles correctly and have "Ambience mode" is:

• disable gpu-next;
• enable "Blend subtitles with video".

So this is Problem with Ambience mode you have to enable the Blend Subtitles with Video when there is .ssa Subs rendering on screen is going in cause Ambient mode streaches screen a little bit on both sides , so when u enable that Blend option it will be properly fixed just one caveat the font would look squeezed slightly and washed out , dont have any fix for that Currently

[tomoro02]

So I did, disabled Next-GPU and enabled "Blend subtitles with video." It works fine, but now I can't use HDR. Is it possible to have "Ambience mode", HDR, and properly displayed ASS/SSA subtitles simultaneously?

[Riteshp2001]

So I did, disabled Next-GPU and enabled "Blend subtitles with video." It works fine, but now I can't use HDR. Is it possible to have "Ambience mode", HDR, and properly displayed ASS/SSA subtitles simultaneously?

all sould work in combination , if it doenst work then i have to see

[tomoro02]

so please check, because as soon as I turn on GPU-next, the subtitles get broken (they are stretched) and turning on "Blend subtitles with video" does not help.

[Chinna95P]

so please check, because as soon as I turn on GPU-next, the subtitles get broken (they are stretched) and turning on "Blend subtitles with video" does not help.

This seems to be an issue present in the subtitle renderer in the gpu-next, no matter what fix is given, it reverts again to the stretched subs format ignoring the manual fix given. Check once with the gpu-next and blend subtitles enabled, and pause the video and see if the stretched subs are showing normally when paused ? and when resumed again, they stretch again

[tomoro02]

Same behavior for me. When I pause, the subtitles are correct, but when I resume playback, the subtitles stretch again.