Animation Flickering on multiple rigid-body scenes

Support Lighting and Rendering
1

Why do some (but not all) animations flicker? I’ve experienced this problem on three scenes so far. The subject is covered in-depth at
http://blender.stackexchange.com/questions/48342/what-causes-rendered-frame-flickering including a bounty offered for a valid answer.

I am stumped and very frustrated! This last flickering animation render makes only the objects (ALL of the objects) suddenly render DARKER, but not the HDR world background.

You can see the aborted render (with bad frames at around 7:20 at: https://www.youtube.com/watch?v=dviikkFAsRQ

You can also see a good/bad still frames comparison at: https://s-media-cache-ak0.pinimg.com/originals/76/43/f6/7643f653d7f87c4a0ba2c70859eed3fa.jpg

There is no z-fighting; there are no hidden objects, no objects on any layer except layer 1, no co-planar polys. This is a simple rigid-body scene with 17,000+ 6-poly cubes (planks) and a one-poly ground plane. There are also two cameras, each parented to an empty, and targeted at an empty. There is one sun lamp, which is completely static (no keyframes). The scene dynamics have been baked. Frames 1-188 are good, but then all objects (except background) begin to flicker DARKER and lighter. Render aborted.

Blender 2.76b and 2.77 get the same flickering when rendered. It doesn’t matter if I render to 8-bit PNG, or 16-bit TIFF.

I’m hoping someone has some insight into this problem, because I’m about to go crazy trying to figure why it is happening so I can fix it.

Thanks for any guidance.

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One additional thought: I’ve seen another post somewhere showing differences between CPU and GPU renders, where there are darker patches in parts of rendered frames on CPU renders, but not on GPU renders. This scene is built on a 2013 MacPro with AMD video cards, on which Blender cannot (or does not?) access the GPU. So I’m wondering if this flickering problem is being caused by CPU rendering.

If so, I need to learn how to report bugs.

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Are you rendering more than one instance on the same computer? Or distributing the render across multiple computers?

Also, can you reproduce the flicker in the Cycles Preview render, or in a final render only?

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Running Blender once only, on one computer. The problem frames happen only in final render, not in preview render.

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I’m still on moderation (as a new user) so my posts take a day or two to show up …

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I believe this problem has finally been SOLVED. The offender was MOTION BLUR. Once I turned it off, renders were all GOOD. I don’t know why this happens; it may be a conflict between Blender and my Graphics Cards (AMD FirePro D500 3071 MB - x2). The darkened frames amount to only 5-7% of any animation when motion blur is turned on, so this may be difficult to nail down for a bug report.

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CORRECTION: Sadly, only SOME of the rendered frames were made good by turning motion blur off and re-rendering. I still have MANY bad frames, even with motion blur turned off. I have NO IDEA why this is happening. This horrid bug has basically cost me more than a week of wasted time. Worst of all, no one really knows why this is happening.