[UE 5.8][MediaViewer] Crash when switching Level Editor viewport type to Cinematic Viewport

POST LINK: https://forums.unrealengine.com/t/ue-5-8-mediaviewer-crash-when-switching-level-editor-viewport-type-to-cinematic-viewport/2747407

POST BODY:

• Summary
  The editor crashes when Media Viewer is viewing/capturing a Level Editor Viewport and the Level Editor viewport type is switched from Default Viewport to Cinematic Viewport. This is not caused by selecting a CineCameraActor itself; the crash happens specifically when switching the viewport type to Cinematic Viewport while Media Viewer is active.

• What Type of Bug are you experiencing?
  Rendering (Graphics / Niagara)

• Steps to Reproduce
  1. Open a UE 5.8 project.
  2. Enable/open the Media Viewer plugin.
  3. In Media Viewer, add or view a Level Editor Viewport.
  4. In the Level Editor viewport dropdown, keep the camera as needed, then change Viewport Type from Default Viewport to Cinematic Viewport.
  5. The editor crashes.

• Expected Result
  Media Viewer should display the Cinematic Viewport, or safely skip rendering/capturing that frame if the viewport render target is unavailable.

• Observed Result
  The editor crashes with an assertion in RenderTargetPool.cpp:

Assertion failed: Texture
File: Engine/Source/Runtime/RenderCore/Private/RenderTargetPool.cpp
Line: 95

• Affects Versions
  5.8

• Platform(s)
  Windows

• Upload an image
  Unable to render embedded object: File (attachment_1.png) not found.

• For crash reports, include your callstack
  UnrealEditor_Core
  UnrealEditor_RenderCore
  UnrealEditor_RenderCore
  UnrealEditor_Engine
  UnrealEditor_Engine
  UnrealEditor_Engine
  UnrealEditor_Engine
  UnrealEditor_MediaViewer
  UnrealEditor_MediaViewer
  UnrealEditor_MediaViewer
  UnrealEditor
  UnrealEditor
  UnrealEditor_RenderCore
  UnrealEditor_RenderCore
  UnrealEditor_RenderCore
  UnrealEditor_RenderCore
  UnrealEditor_Core
  UnrealEditor_Core
  UnrealEditor_Core
  UnrealEditor_RenderCore
  UnrealEditor_RenderCore
  UnrealEditor_Core
  UnrealEditor_Core
  kernel32
  ntdll

• Additional Notes
  Environment:

• Unreal Engine: 5.8.0-55116800+++UE5+Release-5.8
• Platform: Windows 11 25H2
• GPU: NVIDIA GeForce RTX 4060 Laptop GPU
• GPU driver: 581.57
• RHI: D3D12
• Dedicated VRAM reported by UE: 7957 MB

Notes from the crash log:

• MediaViewer is enabled and loaded.
• The crash is an Assert, not an out-of-memory crash.
• MemoryStats.bIsOOM is 0 in CrashContext.runtime-xml.
• Crash occurs in a Slate Paint context while MediaViewer is in the call stack.
• Original crash log contains user/session identifiers, so this report includes only the relevant sanitized details.

POST AUTHOR: danny6

CREATED AT: 08/30/2026 12:02 PM EDT

UPDATED AT: 10/19/2026 12:48 PM EDT

1. Open a UE 5.8 project.
2. Enable/open the Media Viewer plugin.
3. In Media Viewer, add or view a Level Editor Viewport.
4. In the Level Editor viewport dropdown, keep the camera as needed, then change Viewport Type from Default Viewport to Cinematic Viewport.
5. The editor crashes.