Render video output with Alpha Channel

brahmzxc · July 22, 2019, 04:45:09 AM

How to render a video with Alpha Channel in Keyshot 8.2 ?

mattjgerard · July 22, 2019, 05:53:37 AM

PNG Frames with transparency, then assemble the frames in a video editor.

brahmzxc · July 22, 2019, 09:51:09 PM

But that doesn't looks smooth for 60 FPS.

Eugen Fetsch · July 22, 2019, 11:27:40 PM

Did you check the playback speed in your 3rd party composition? Mostly it's set to 24/25 or 30 fps. If it was set to 60 fps so maybe the player/viewer can't handle videos with alpha channel well - try a different one.

mattjgerard · July 23, 2019, 07:05:19 AM

What are you using to composite the video layers?

Eugen Fetsch · July 23, 2019, 08:46:33 AM

Blackmagic Fusion, Blackmagic Davinci Resolve, Blender or After Effects (depends on the project).

It's very rare that my clients ask for videos with alpha channel - I'm not in the broadcasting or stock footage business

But if it happens "Apple ProRes 4444" or "Avid DNxHD / DNxHR" do the job very well.

List of codecs: https://www.digitalrebellion.com/blog/posts/list_of_video_formats_supporting_alpha_channels

brahmzxc · July 23, 2019, 09:48:48 PM

I use after effects for compositing of the PNG files with transparency.
But I have tried one trick for your video to be transparent - In the keyshot itself make the environment green color same as like chroma screen. Now render the video in AVI, MOV or MP4 whatever you like. After this import the video in After effects and apply Keylight and click on the green color on the background. VOILA!!! your video is now transparent, you can apply any color or any background of your choice.

Eugen Fetsch · July 23, 2019, 10:45:04 PM

Why use chroma keying if you can render with alpha?

It will never be good, especially if you use motion blur or/and depth of field. With MB and DOF it will be a pain.
Compositing is not that tricky and there are dozens free tools on the market.

INNEO_MWo · July 24, 2019, 01:35:28 PM

Thank you Eugen for your professional advice. I will bookmark this forum entry to look into it if I need alpha next time.

And I hope that the alpha video project will be finished happy.

Cheers
Marco

mattjgerard · July 25, 2019, 05:57:04 AM

Quote from: brahmzxc on July 23, 2019, 09:48:48 PM
I use after effects for compositing of the PNG files with transparency.
But I have tried one trick for your video to be transparent - In the keyshot itself make the environment green color same as like chroma screen. Now render the video in AVI, MOV or MP4 whatever you like. After this import the video in After effects and apply Keylight and click on the green color on the background. VOILA!!! your video is now transparent, you can apply any color or any background of your choice.

I'll have to check this, but the last time I rendered with a colored background, it did influence the render in the reflections and caustics. 99% of the time I render on white (2%) or with an alpha(97%). So unless you have a very simple object and animation, I'd be worried about the green sneaking around corners and into reflections that would get keyed out later.

theAVator · July 25, 2019, 06:36:42 AM

I use the Chroma Key thing as well and have not had any issues with it - however, I use the straight frame outputs only, I don't output video from KS. I think if you have KS output a AVI or MOV or whatever you have a better chance of experiencing bleed and such as you're pre-processing the frames into video. Importing the frame stack right into Premiere you're working with the raw frames and I feel get a much cleaner/crisper result. The key should pull out the color from the whole image (reflections/shadows/highlights/etc) in varying values - i.e. the full green background would be 100% take-out whereas some green in a ground shadow might only be a 5% take-out.

PNG frame outputs with Alpha also works, but in the past I had run into issues when doing fade animations on transparency.