Hardware transcoding to overlay an embedded PGS subtitle track positions them below the visible screen

[Grimmer 15]

The movie is transcoded in HD (1920x804 = 2.39:1) and the mkv contains 1 PGS subtitle track.  When I activate the subtitles, it is hardware transcoded as usual; however, the subtitles "appear" below the visible screen.  If there are two lines of text, the tip of the top line is visible.

Emby hardware transcoded screenshot:

Played the same file directly with VLC:

I have tried a zillion combinations for the Emby server subtitle options, including: Enabling and disabling the OCR option X Changing the position and color of the subtitles X re-transcoding the file with and without the black bars top and bottom.  They all result in the same always white and mostly hidden text when transcoded by Emby and normal when played directly through VLC.

Anything else I can try to fix it?  I believe, but haven't truly qualified, whether or not this has always been going on since I switched to Mint Linux from the previous Synology.

I also just ran a test by disabling the hardware transcoding, and as I have suspected, it appears to be the hardware transcode that is not positioning the subtitles correctly.  The software transcode looks just like the VLC screenshot above.  Is this a known issue with Raptor Lake GPU and Mint 22.2, kernel 6.14.0-33-generic?  Would it help to try to upgrade the server's GPU drivers?

ffmpeg-transcode-fea809d1-feb4-453d-878c-148c3661113c_1.txt

[Grimmer 15]

I have found that the location of the subtitles randomly appears to be correct, although at a much lower frequency.  I.e. starting and stopping the transcoding would sometimes result in correctly placed subtitles (via hardware transcoding).  They were in the wrong place, then I switched the audio stream to one that didn't require transcoding, which restarted the transcode and the subtitles moved to the correct position.  I experimented with doing this over and over in different combinations and less than 10% of the time the subtitles were fixed, seemingly randomly.

I only did the software transcode test once, so there is a chance that it was a random fluke rather than actually fixing the issue.

[Luke 42077]

Hi, I think what's happening is we are assuming the subtitles are 1080p. Sometimes they are not and need to be scaled approximately. So that's something we need to look at.