VSE: Blend Modes on Scenes do not layer properly
Open, Needs TriagePublic

Description

System Information
macOS Sierra (NVIDIA GeForce GTX 775M

Blender Version
Broken: 2.78 (2017-03-07 Hash: 15fa806)
Worked: 2.78 (2017-02-06 Hash: f7eaaf3)

Short description of error
When using the Blend option for Scenes, using anything other than Replace behaves, essentially, like Replace. So when I add a Scene and try to use Alpha Over on top of a video, the render output only shows the Scene (text and a black screen, in my case).

Exact steps for others to reproduce the error

  1. In the VSE, add a video or image to Channel 0.
  2. Add a Scene with no background to Channel 1.
  3. In the Scene Properties, select "Alpha Over" as the Blend. Then scroll down to Preview and choose "Transparent" as the Alpha Mode.
  4. Render the frame as a PNG, or render the animation as a Ffmpeg file. I've gotten the same results either way.
  5. The Scene replaces the video or image placed in channel 0, showing only the scene and a dark background.

(Included, please find a zip file with appropriate files to recreate this issue; to recreate, switch to the VSE, change to the MainVideo scene, and hit Render or Animation)

Details

Type
Bug

Your 'Text' scene needs to have transparency enabled in its render settings, enable that and transparency in the vse should work fine.

Your 'Text' scene needs to have transparency enabled in its render settings, enable that and transparency in the vse should work fine.

Please specify where in the Render settings you are referring to. Here's what I have tried:

  1. There is a "Transparent" check box in the Film pane of the Render Settings. I checked that in the Text scene, and that didn't fix it -- the background shows as transparent, but the VSE (in the MainVideo scene) still behaves as though the Blend mode is "Replace"
  2. If you are referring to the Strip properties pane in the VSE with the "Text" scene, there is an "Alpha Mode" drop down with the "Transparent" option inside -- it is on, and doesn't make a difference.

Please note I have tried the attached file in the "Worked" version I noted above -- it renders as expected in that version with no changes, but not the latest nightly build.

Side note: I realize that I forgot to specify which Scene to Render in -- the Scene to have open in VSE is MainVideo. I've updated the original text.

ok, in the file you provided, the 'transparent' checkbox in the render properties of the 'Text' scene is not checked, that does need to be enabled for proper transparency in the scene strip, and it fixed it on my computer at least (on 2.78c). You should probably change that in the example file.

I can confirm the bug in the latest build tho, blender seems to 'know' that it should be transparent (it shows the checkerboard background in the preview), it just doesn't mix it.

ok, in the file you provided, the 'transparent' checkbox in the render properties of the 'Text' scene is not checked, that does need to be enabled for proper transparency in the scene strip, and it fixed it on my computer at least (on 2.78c). You should probably change that in the example file.

I can confirm the bug in the latest build tho, blender seems to 'know' that it should be transparent (it shows the checkerboard background in the preview), it just doesn't mix it.

I am seeing this problem in the nightly build as well, not in 2.78c.

As an aside, the Transparent box you're talking about isn't necessary for the Blend to work properly in VSE -- changing the Alpha Mode in the VSE Strip Properties channel is (normally) sufficient.