Maniphest T79869

Eevee motion blur doesn't work correctly when slowed down scene is rendered from VSE
Closed, Resolved
Actions

Assigned To
Richard Antalik (ISS)
Authored By
Gehrig (otterremixchamp)
Aug 18 2020, 6:55 AM
Tags
  • EEVEE & Viewport
  • BF Blender (2.91)
Subscribers
Clément Foucault (fclem)
Gehrig (otterremixchamp)
Richard Antalik (ISS)

Description

System Information
Operating system: windows 10
Graphics card: RTX 2080 Ti

Blender Version
Broken: (2.9, master, August 17 2020)
Worked: n/a, Cycles motion blur works correctly

Short description of error
When using speed control effect on a scene, it does not interpolate keyframes in the same way as it does when NOT using motion blur, or when using cycles. It just renders the same frame over and over when slowing down speed, and skips frames when raising speed. It shows in the preview window fine within blender, it's only when rendered. Rendering an image sequence has the same issue as rendering straight to movie file.

Exact steps for others to reproduce the error
Based on the default startup or an attached .blend file (as simple as possible).

  • Open "Scene" scene, and set render engine to eevee, and turn on motion blur.
  • Open "Edit" scene, and go to the video editing workspace.
  • Check the Speed control effect, and see that Speed Factor is set to 0.2
  • Render animation. Check video file (or image sequence) and see that when time is slowed down, it just renders the same frame over and over instead of interpolating frames.
  • Turn off motion blur in the "Scene" scene. Go back to "Edit" scene, and render new animation. See how it interpolates key frames as expected.

Thanks! Hope you have a wonderful day.

bugreport.blend949 KBDownload

Related Objects

Event Timeline

Gehrig (otterremixchamp) created this task.Aug 18 2020, 6:55 AM
Richard Antalik (ISS) closed this task as Archived.Aug 20 2020, 4:47 AM
Richard Antalik (ISS) claimed this task.
Richard Antalik (ISS) added a subscriber: Richard Antalik (ISS).

Thanks for the report, but the issue reported here is a request for modified/improved behavior and not a bug in current behavior.
What you expect could be in theory implemented with eevee, I am not so sure about cycles. But I am not sure if this won't require changes in rendering engine and even motion blur implementation. Speed effect really just renders one frame multiple times or skips frames as you correctly pointed out.

Currently best workaround seems to be using time remapping in Output Properties in "Scene" scene instead of speed control effect.

Closing as this bug tracker is only for bugs and errors.
For user requests and feedback, please use other channels: https://wiki.blender.org/wiki/Communication/Contact#User_Feedback_and_Requests
For more information on why this isn't considered a bug, visit: https://wiki.blender.org/wiki/Reference/Not_a_bug

Gehrig (otterremixchamp) added a comment.Aug 20 2020, 9:10 AM

Hi Richard!

I'm not quite sure we're on the same page, it's very likely I did a bad job of explaining the situation. The Speed effect in the VSE creates new frames when you use a different "scene" as a movie strip, it just doesn't work when motion blur is turned on (eevee). That's the only situation I've seen where it just renders the same frame multiple time.

I've attached two jpg sequences to show you the feature in action since there's confusion on what I'm talking about. I'm using the previously attached .blend file, with a couple modifications to make my point clear. The new 2.9 has a bug that won't let you open this blender file (just reported it) so this was tested in 2.83 LTS. I'm happy to also recreate in an older version of 2.9, but this is just to show you the feature working in general so we can make sure we're on the same page.

The scene "Animation" has a cube cross from the left side of the screen, to the right side of the screen, in 60 frames, at 30fps.

bugreport - Copy.blend937 KBDownload

Examples.zip4 MBDownload

Example_1
This is rendered from the "Edit 1" scene. All I've done is add the "Animation" scene as a strip, and export a jpg sequence. 60 frames at 30fps.

Example_2
This is rendered from the "Edit 2" scene. I've added a Speed effect strip that reduces time by a speed factor of 0.5. Please notice that now the animation takes 120 frames to complete, and Blender automatically added frames in between each old frame. There are NO multiple frames, or skipped frames.

This doesn't work with eevee when motion blur is turned on. It does work in Cycles with motion blur turned on as far as I've seen. I'm sorry if anything I'm saying is unclear, or I'm misunderstanding what you're saying. Thanks Richard!

Cheers,
Gehrig

Richard Antalik (ISS) reopened this task as Confirmed.Aug 21 2020, 1:18 AM
Richard Antalik (ISS) added a project: EEVEE & Viewport.

Thanks for clarification. My assumption was wrong, and I should tested it first.
This should work if it works with cycles.

Richard Antalik (ISS) renamed this task from Speed control adjustment layer does not work correctly with Eevee when using motion blur to Eevee motion blur doesn't work when slowed down scene is rendered from VSE .Aug 21 2020, 1:26 AM
Richard Antalik (ISS) renamed this task from Eevee motion blur doesn't work when slowed down scene is rendered from VSE to Eevee motion blur doesn't work correctly when slowed down scene is rendered from VSE .
Richard Antalik (ISS) updated the task description.
Gehrig (otterremixchamp) added a comment.Aug 21 2020, 2:10 AM

Sounds good! Thank you for checking out my reply, my description wasn't very good when I first posted the bug, it's my first time reporting a bug, I'll do better next time :D. Thank you Richard, I hope you have a great weekend!

Clément Foucault (fclem) moved this task from Backlog to Blender 2.91 on the EEVEE & Viewport board.Sep 15 2020, 3:23 PM
Clément Foucault (fclem) edited projects, added BF Blender (2.91); removed BF Blender.
Clément Foucault (fclem) closed this task as Resolved.Oct 13 2020, 6:33 PM
Clément Foucault (fclem) added a subscriber: Clément Foucault (fclem).

I think this was related to T80086. Which has been solved. I'll close this report since I cannot reproduce the issue anymore. Feel free to reopen if that's still the case for you.