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Maniphest T52583

Background rendering with frame jump and sequencer is broken
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Description

System Information
Linux Ubuntu 16.04, Intel integrated graphics card

Blender Version
Broken: at least from 2.76b to latest build

Short description of error
While rendering in the background from the command line a scene with a non-empty video sequencer, the jump parameter is ignored and the incorrect frames are rendered.

Exact steps for others to reproduce the error
Consider the attached bug.blend file

bug.blend432 KBDownload
and run in the terminal the command

blender -b bug.blend -a

Now all the 30 frames are correctly created.

If, instead, the couple of commands

blender -b bug.blend -s 1 -j 2 -a
blender -b bug.blend -s 2 -j 2 -a

is run, the wrong frames are generated. In particular, the second command generates the even-numbered frames but with the contents of the odd-numbered frames. Moreover, the terminal output highlights the inconsistency:

Fra:29 Mem:16.95M (0.00M, Peak 17.47M) | Time:00:00.58 | Remaining:00:00.00 | Mem:0.49M, Peak:0.87M | Scene, RenderLayer | Path Tracing Tile 132/135
Fra:29 Mem:16.89M (0.00M, Peak 17.47M) | Time:00:00.58 | Remaining:00:00.00 | Mem:0.43M, Peak:0.87M | Scene, RenderLayer | Path Tracing Tile 133/135
Fra:29 Mem:16.83M (0.00M, Peak 17.47M) | Time:00:00.58 | Remaining:00:00.00 | Mem:0.36M, Peak:0.87M | Scene, RenderLayer | Path Tracing Tile 134/135, Sample 3/10
Fra:29 Mem:16.77M (0.00M, Peak 17.47M) | Time:00:00.58 | Mem:0.30M, Peak:0.87M | Scene, RenderLayer | Path Tracing Tile 135/135
Fra:29 Mem:16.77M (0.00M, Peak 17.47M) | Time:00:00.58 | Mem:0.30M, Peak:0.87M | Scene, RenderLayer | Finished
Fra:29 Mem:16.43M (0.00M, Peak 17.47M) | Time:00:00.58 | Sce: Scene Ve:0 Fa:0 La:0
Fra:29 Mem:34.25M (0.00M, Peak 44.14M) | Time:00:00.62 | Sce: Scene Ve:0 Fa:0 La:0
Fra:29 Mem:34.25M (0.00M, Peak 44.14M) | Time:00:00.62 | Sce: Scene Ve:0 Fa:0 La:0
Saved: '/tmp/0028.png'
 Time: 00:00.67 (Saving: 00:00.04)

where frame 29 is elaborated but frame 28 is saved.

Related Objects

Event Timeline

Massimiliano Leoni (massimiliano.leoni) created this task.Aug 29 2017, 3:43 PM
Campbell Barton (campbellbarton) mentioned this in T52586: Disable scenes using themselves as sequence strips 2.8 Proposal.Aug 30 2017, 3:35 AM
Campbell Barton (campbellbarton) mentioned this in D2815: Fix T52586: Rendering a frame range no longer modifies the scene.Aug 30 2017, 4:01 AM
Campbell Barton (campbellbarton) added a subscriber: Campbell Barton (campbellbarton).EditedAug 30 2017, 4:33 AM

This is a problem with using the same scene as a strip in your sequence.

Setting the start frame also offsets it's position in the sequencer.

I've made a patch to support this - D2815, although I'm not convinced the fix is a net gain.

For 2.8x it may be best to remove this ability, see: T52586

Campbell Barton (campbellbarton) lowered the priority of this task from 90 to 50.Aug 30 2017, 6:33 AM
Massimiliano Leoni (massimiliano.leoni) added a comment.Aug 30 2017, 12:44 PM

Ok, so perhaps I am using the feature the wrong way? Suppose I want to superimpose a logo on a part of the strip. What I would do is to load the image on another channel of the VSE and use a transform to add it to the scene. Should I do it differently? Should I put everything into another scene? Maybe I can achieve the same with the compositor...

Another use case would be to stop the animation at some point to have an explanatory text appear, to later resume the animation. What's the correct way to do these things?

Campbell Barton (campbellbarton) added a comment.Aug 30 2017, 12:47 PM

It's best to have a scene that's only for editing video - so you don't put the scene into its self (causing this bug).

Massimiliano Leoni (massimiliano.leoni) added a comment.Aug 30 2017, 1:59 PM

I can confirm that using another scene works as expected. Thanks for the advise, I also noticed that inputting the same scene in the VSE brings some inconveniences.

Campbell Barton (campbellbarton) closed this task as a duplicate of T30663: Rendered frame shifted while using sequencer.Aug 31 2017, 6:33 AM