Nope, can't replicate that, everything works fine.

I just had a play with other Compositing Modes & the Compositing Modes in Parent tracks. still worked fine.

@Gid Please try with this clip. It is with black background. use ADD compositing mode.

https://drive.google.com/file/d/1kQ88eSag9Xk3LpPwOIgAmm51jJEjmDSu/view?usp=sharing.

@iEmby I had a play with it for quite a while, I couldn't get Vegas to make the black flashes in your video.

Here's just 12mins of me playing with it but I played for an hr or more.

In this I added a couple of masks in the last bit but that was to restrict the boundaries of the flash, not because of any type of black image flashing like in your video.

@iEmby I don't think the nested timeline feature works correctly. The parent becomes corrupted and the nested timeline becomes what the parent was, except that the Add composite turns into a Source Alpha. The whole thing is messed up. Forget the whole thing. Same thing in 21, 22, and 23.

@Gid

Please look at this video

may be u understand what i am saying.

by the way u r doing one thing wrong while reproduction of this problem.

sry for my English in advance.

@Robert Johnston

yes.. sir

you understand the issue properly.

thankyou.

@iEmby Ah, ok I see.

Nope, sorry I can't make that work either, I tried alsorts but still get the same result as you.

When you create a nested timeline from within VEGAS by selecting events and clicking on the "Create or open nested timeline" button, the software warns you about this kind of issues if it detects there may be a problem:

Just a general comment on nested timeline, I am using it on VP23 (still on build 356!) in a current project of mine, and I am not having issues with it.
@LdM_Edit I know you can create a nested timeline using that method, but I usually use nesting in a different workflow: whenever I feel the main project has a piece which I feel will get too complex with a lot of FX or a lot of tracks, I save my main project under a different name (e.g. "nest_x"), delete all the stuff before and after the piece I want to be nested, and complete as a new "main" project what it needs to be for my future nest. Then I open my old main project and drop the renamed main .veg (e.g. "nest_x") at the position I want it as nest.
 

I always try to avoid nesting, because it makes previewing and rendering terribly slow. If a project becomes to complex (too many tracks) you can easily group different tracks and collapse them into just one track, which always quickly can be expanded again to edit the different tracks.

example:

before: and

after:

Also I work always with short subprojects, render them separately and merge those subprojects lossless to a main project with Shutterencoder, an action that takes just a few secondes/minutes.

Just a general comment on nested timeline, I am using it on VP23 (still on build 356!) in a current project of mine, and I am not having issues with it.
@LdM_Edit I know you can create a nested timeline using that method, but I usually use nesting in a different workflow: whenever I feel the main project has a piece which I feel will get too complex with a lot of FX or a lot of tracks, I save my main project under a different name (e.g. "nest_x"), delete all the stuff before and after the piece I want to be nested, and complete as a new "main" project what it needs to be for my future nest. Then I open my old main project and drop the renamed main .veg (e.g. "nest_x") at the position I want it as nest.
 

Just tried that, it still doesn't work with @iEmby example 🤷‍♂️

​​​​​@Gid It doesn't matter how you create the nested project. The issue is that @iEmby expects that the "fake" transparency created by the "add" composition is taken over in the nested project. You see already in the thumbnails of the nested event that this is not the case.

@3POINT Yeah, I'm just trying to make it work & guess the point of my last post is to show that it doesn't matter how the nest is created.

PS. If it was me I wouldn't use the nest option, I'd just apply it to the main timeline as suggested.

@Gid +1

I hope that Vegas team is still working on this:

because at the moment to me the nesting feature is almost useless/unworkable. I like the way it works in DR, where you can create extra timelines and/or compound clips, which has almost no influence on preview and rendering speed.

Yep, I think I'm on board with the OP in that whatever fx, composite mode etc. I add to a nest should transfer to the timeline in the same way. But it doesn't, whether that is intended/expected behaviour or not. Broken, poorly written code or overlooked 🤷‍♂️. As it doesn't achieve the desired result I'd choose an alternate route.

PS. I was playing with this & tried using BCC+Maths Composite. Vegas track composites are 'maths' composites, therefore when Add is applied it's making a calculation IE it's taking black 0 & adding it to whatever it's compositing onto. If the file it's compositing onto has an alpha/transparent are is that area also 0. ..? 0 minus 0 = 0 (black). or is that bollocks? 🤦‍♂️🤣

I tried rendering just the flash with Add applied to Prores 444 + Alpha, but got no alpha channel, no transparency in the rendered file just black. Vegas or basic maths can't render 0 (Add) + 0 (alpha channel)

That's what I said, @iEmby wants to create a "fake" transparency of something that is original black. If that would work there would be no need for a alpha channel video with transparency.

@iEmby You can still nest the old-fashioned way by manually loading a Veg file as media, and the composite will work. Just don't use those nesting buttons to go back and forth.

@iEmby You can still nest the old-fashioned way by manually loading a Veg file as media, and the composite will work. Just don't use those nesting buttons to go back and forth.

@Robert Johnston Did you not bother reading/watching my post?

Just a general comment on nested timeline, I am using it on VP23 (still on build 356!) in a current project of mine, and I am not having issues with it.
@LdM_Edit I know you can create a nested timeline using that method, but I usually use nesting in a different workflow: whenever I feel the main project has a piece which I feel will get too complex with a lot of FX or a lot of tracks, I save my main project under a different name (e.g. "nest_x"), delete all the stuff before and after the piece I want to be nested, and complete as a new "main" project what it needs to be for my future nest. Then I open my old main project and drop the renamed main .veg (e.g. "nest_x") at the position I want it as nest.
 

Just tried that, it still doesn't work with @iEmby example 🤷‍♂️