I would like to report a severe bug/pipeline stall that occurs when exporting video sequences in Twinmotion.
Issue Description: Whenever I render a video in Lumen mode containing an animated video material (an MP4 file applied to an emissive surface such as a TV screen or an LED billboard), the GPU completely stops processing.
The GPU utilization drops to nearly 0% - 1% (monitored via Task Manager).
The export process stalls dramatically: a simple 10-second sequence takes several hours to render.
This issue appears to persist across different versions of the software.
Expected Behavior: The GPU should maintain normal utilization to accelerate the Lumen rendering pipeline, and the video export should complete within a reasonable timeframe.
Steps to Reproduce:
Open a scene with Lumen enabled (Global Illumination & Reflections).
Assign an MP4 video file as an emissive/diffuse texture to a screen or display mesh.
Set up a short video sequence (e.g., 10 seconds) and start the export.
Check GPU load in Task Manager — the GPU remains completely idle while render time skyrockets.
Please investigate this issue, as it creates a critical bottleneck when working with animated media screens.
A GPU sitting at 0-1% means the export is not GPU-bound. The render thread is blocked waiting on the MP4, so Lumen never gets the next frame. A 10 second shot turning into hours is that stall, not Lumen running out of GPU. Lumen only makes it worse, because each frame is already slow and the video texture waits in between them.
Twinmotion’s video material is a media texture. Offline export does not advance that player the way the viewport does, and the exporter ends up syncing on the CPU decoder.
What actually finishes the export:
Replace the MP4 on the TV or LED with an image sequence (PNG or JPEG frames) and play that as a flipbook or animated texture. Same picture, no media player, and the GPU stays busy. This is the reliable fix.
If the MP4 has to stay for a test, export 1 second at low resolution. If that also sits at 0% GPU, the video material is the stall, not the scene.
Remove every other media source in the scene while you test. Each video texture can stall on its own.
Export once with Lumen off, as a control. If the MP4 is fast with Lumen off and dead with Lumen on, you still want the image sequence. Lumen plus a stalled media texture is the combination that stretches a short shot into hours.
A driver update will not fix a thread that is waiting on the decoder. The image sequence is what keeps Lumen and gives the GPU work again.
