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Scene Strip playback fps regression
Confirmed, NormalPublicKNOWN ISSUE

Description

System Information
Operating system: Windows-10-10.0.17763 64 Bits
Graphics card: Intel(R) UHD Graphics 600 Intel 4.5.0 - Build 24.20.100.6137

Blender Version
Broken: version: 2.80 (sub 75), branch: master, commit date: 2019-07-29 14:47, hash: rBf6cb5f54494e
Worked: (2.79)

In 2.79:
Duplicate the scene(with a camera inside).
Select the new scene.
Open the Video Editor workspace.
Add a scene strip from the first scene.
Set the Render Resolution to 100.
Save the file.

Do the same thing in 2.80.

Open both files in two different instances of Blender 2.80 and compare the playback speed, after setting both to Workspace > View Transform > Standard.

The file generated in 2.79 I get a playback rate of 16-20 fps.

The file generated in 2.80 I get a playback rate of 9-11 fps.

I tried to look through the settings to find any differences, but I couldn't find any, but there must be a difference in the settings causing this regression?

A gif of the playback rates:

Event Timeline

Bastien Montagne (mont29) lowered the priority of this task from 90 to 30.Sep 25 2019, 1:54 PM

There is one major difference between those two files - the 2.80 one uses nodes for its cube material, while the 2.79 does not. Please check whether removing that difference in one way or the other also fixes the fps differences.

Also please Try the latest build from our buildbot.

It is actually like 2 fps faster with the node texture on(on a build I did this morning), so that doesn't explain the difference in playback rate.

Then that’s likely a driver issue (here on linux, on an Haswell GPU, both files run above 24fps - in a debug build!). Please install the latest official drivers.

Thanks for the suggestion, but updating the driver doesn't change anything here.

Maybe you'll see the difference if you set the render fps to something which will put a strain on your system like 100 fps or 4k video, and the see if both files are played back at the same fps. If they are then maybe this is a Windows related problem?

[Edit: Tried on another faster computer and playing the two files(and changing the fps to 60) resulted in 2.79 file was playing 37 fps and 2.80 file 30 fps]

Bastien Montagne (mont29) raised the priority of this task from 30 to 90.Oct 14 2019, 12:02 PM

Not sure whether that difference in speed is expected, maybe @Jeroen Bakker (jbakker) or @Clément Foucault (fclem) would know more? Or maybe @Sergey Sharybin (sergey), although I would not expect depsgraph to be a bottleneck with such a simple scene…

@Bastien Montagne (mont29), can you reproduce the issue? For me both files are around 75 to 100 fps (jumping between those values).

@Peter Fog (tintwotin), if there are two files which has different fps in the same version of Blender there must be a setting which is different across those files. It is not just a color management which affects on this. Try figuring this out. Is easier for someone who can reproduce the issue.

@Sergey Sharybin (sergey) nope, for me as well speed are very high and similar.

Some time ago did @Ray molenkamp (LazyDodo) profile the export of the default cube with ffmpeg and in that case it was color management(implemented in april?), which caused slower exports. Maybe scene strip playback is affected by this too, but some non-ui option is set differently between 2.79 and 2.80?


https://blender.chat/channel/vse?msg=k55ZbMCjSHMBavDtK

@Peter Fog (tintwotin), if there are two files which has different fps in the same version of Blender there must be a setting which is different across those files. It is not just a color management which affects on this. Try figuring this out. Is easier for someone who can reproduce the issue.

I have been comparing the UI settings of those two files, and didn't find any difference, but it feels like looking for a needle in a haystack. Are there any ways two .blend files can be compared, or could 2.80 changes to the file format give a clue?

Richard Antalik (ISS) changed the task status from Needs Triage to Confirmed.EditedJan 13 2020, 5:06 PM
Richard Antalik (ISS) changed the subtype of this task from "Report" to "Known Issue".

Can confirm regression(2.79 vs 2.83) with lots of subdivided cubes or empty scene with camera.

I looked into reason for this quite long time ago and it looks like reading memory from GPU is slow.
I didn't compare this to 2.79 code though, and I don't have good knowledge of openGL workings, so I don't exactly know root cause of regression and if it's easy to optimize the code.

Before I can dive into this and know more, I will treat this as a known issue.

For whatever it is worth, eevee rendered scene strips are playing painfully slow compared to the playback of eevee rendered in the 3d view(gif):