PGS subtitles burned partially behind black bars after enabling hardware acceleration (P2200 / Intel UHD 630)

[warmovies 0]

Emby Server 4.9.5.0 running on Windows 11.

Hardware:

• Dell Precision 3630
• Intel i7-9700
• NVIDIA Quadro P2200
• Intel UHD 630 also available

Nearly all of my Blu-ray rips contain PGS subtitles.

Prior to enabling hardware acceleration, PGS subtitles displayed correctly.

After enabling hardware acceleration, subtitles are now rendered partially behind the lower black letterbox bar and are often totally or mostly unreadable.

Observations:

• Problem occurs on Roku Ultra 4850X.
• Problem also occurs in the Emby Web App running in Microsoft Edge on the server itself.
• SRT subtitles display normally.
• PGS subtitles are affected.
• Emby dashboard shows "Burning in subtitles."
• Transcoding is hardware accelerated and working correctly.
• Quadro P2200 NVDEC/NVENC are functioning normally.

I have tested:

• Monitor connected directly to P2200.
• Monitor connected to Intel UHD 630 motherboard output.
• Same result.

Because the issue occurs on both Roku and Edge Web App, it appears the subtitle positioning problem is occurring during Emby's subtitle burn-in/transcoding process rather than at the client.

Has anyone seen PGS subtitles shifted into the black bars after enabling hardware acceleration?

Is there a known interaction with NVDEC/NVENC, DX11VA, Quick Sync, or subtitle burn-in positioning?

The three screenshots are of quicksync, nvenc, and software acceleration. The subs that are properly rendered and readable is the software acceleration which means acceleration is turned off. I have emby premiere and have zero issues with software acceleration and zero issues with dvd subtitles DVDSUB. 4:3 for obvious reasons in bluray subs work just fine as do 16:9. 

[pwhodges 2065]

In my experience this can happen when media has been re-encoded to crop encoded black bars from the video.  The subtitles were made to match the original size of the video (including encoded black bars), and resizing them to fit into the cropped video gets missed out somewhere.  These days I avoid cropping when re-encoding for just this reason.

Paul