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

General Issues and Bug Reporting (Unreal Engine)
1

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

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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.