dcpomatic with grok - Encoding stuck when burning subtitles into image

[Guddu]

I purchased a grok license and when encoding a DCP, it is getting stuck at 540th frame. If I disable GPU Acceleration then I am able to encode it without any issues but with grok it hangs at 540th frame.

My setup is as follows
dcpomatic 2.18.37
Ubuntu 24.04
GeForce RTX 2080
NVIDIA-SMI 580.126.09
Driver Version: 580.126.09
CUDA Version: 13.0

Here is the log from the run

Sun 05 Apr 2026 07:34:56 PM -04: DCP video rate 24 fps
Sun 05 Apr 2026 07:34:56 PM -04: Video bit rate 150000000
Sun 05 Apr 2026 07:34:56 PM -04: Transcode job starting
Sun 05 Apr 2026 07:34:56 PM -04: Thread counts from: grok=yes, only_servers=no, master=16
Sun 05 Apr 2026 07:34:56 PM -04: Making threads: CPU=0, GPU=16, Remote=0
Sun 05 Apr 2026 07:34:56 PM -04: Sub-job Encoding starting
Sun 05 Apr 2026 07:34:59 PM -04: [GROK] ./grk_compress -batch_src GRK_MSGR_BATCH_IMAGE,1998,1998,1080,3,12 -out_fmt j2k -k 1 -G 0 -cinema2K 24,150000000 -J https://grokcompression.com/api/register -v
Sun 05 Apr 2026 07:35:00 PM -04: ERROR: Failed to schedule encode of 541 using grok
Sun 05 Apr 2026 07:35:00 PM -04: ERROR: Failed to schedule encode of 542 using grok
Sun 05 Apr 2026 07:35:00 PM -04: ERROR: Failed to schedule encode of 540 using grok
Sun 05 Apr 2026 07:35:00 PM -04: ERROR: Failed to schedule encode of 543 using grok
Sun 05 Apr 2026 07:35:00 PM -04: ERROR: Failed to schedule encode of 544 using grok
Sun 05 Apr 2026 07:35:00 PM -04: ERROR: Failed to schedule encode of 545 using grok
Sun 05 Apr 2026 07:35:00 PM -04: ERROR: Failed to schedule encode of 546 using grok
Sun 05 Apr 2026 07:35:00 PM -04: ERROR: Failed to schedule encode of 547 using grok
Sun 05 Apr 2026 07:35:00 PM -04: ERROR: Failed to schedule encode of 548 using grok
Sun 05 Apr 2026 07:35:00 PM -04: ERROR: Failed to schedule encode of 549 using grok
Sun 05 Apr 2026 07:35:00 PM -04: ERROR: Failed to schedule encode of 550 using grok
Sun 05 Apr 2026 07:35:00 PM -04: ERROR: Failed to schedule encode of 551 using grok
Sun 05 Apr 2026 07:35:00 PM -04: ERROR: Failed to schedule encode of 552 using grok
Sun 05 Apr 2026 07:35:00 PM -04: ERROR: Failed to schedule encode of 553 using grok
Sun 05 Apr 2026 07:35:00 PM -04: ERROR: Failed to schedule encode of 554 using grok
Sun 05 Apr 2026 07:35:00 PM -04: ERROR: Failed to schedule encode of 555 using grok

I have determined this to be happening "only" when I use Subtitles with "Burn Subtitles into image" option selected.

Test 1 - grok enabled. No Subtitles files - DCP encodes fine.

Test 2 - grok enabled. Subtitles files loaded with "Burn Subtitles into image" option unchecked - DCP encodes fine.

Test 3 - grok enabled. Subtitles files loaded with "Burn Subtitles into image" option checked - DCP does not encode. Gets stuck at the frame where the first subtitle needs to show up.

Test 4 - grok enabled. Subtitles files loaded. A minimal file with just 1 subtitle and "Burn Subtitles into image" option checked - DCP does not encode fine. Gets stuck at the frame where the first subtitle needs to show up.

With grok disabled, all the above tests result in the DCP encoding just fine.

[boxerab]

Fix is here

https://github.com/cth103/dcpomatic/pull/40