<p>The alphaextract/alphamerge filters are meant for this.</p>

<p>Since your alpha reference is already greyscale, we only need the alphamerge filter</p>

<pre><code>ffmpeg -i main.mp4 -i alpha.mp4 -filter_complex [0][1]alphamerge,format=yuva420p -c:v libvpx -auto-alt-ref 0 out.webm
</code></pre>

CC BY-SA 3.0
2018-04-09T10:53:24.187Z
Wonderfull! A perfect result with b/w and complex greyscale alphaemulated movies:). Now i can relaxed wait that my Videoediting and Animating Software implement this automatically.
CyberPunkBln
CC BY-SA 3.0
2018-04-09T10:41:21.823Z
2018-04-09T10:41:21.823Z
Gyan
<p>I have 2 video files. One file is the main content and the other file has an alpha channel emulated with black and white (white = opacity 100 and black = opacity 0). Sometimes the emulated alpha channel file has only full black and full white frames, but I think some videos that I want to create will have complex alpha channel emulation with gray scales.</p>

<p>Is it possible to make with ffmpeg an vp8,vp9 -pix_fmt yuva420p ready .webm movie?</p>

<ffmpeg><alpha><vp9>
Create Alpha channel-Videos (obs stinger compatible) with ffmpeg and 2 files
CyberPunkBln
# Create Alpha channel-Videos (obs stinger compatible) with ffmpeg and 2 files

(Asked by: username_0 on 2018-04-09)

I have 2 video files. One file is the main content and the other file has an alpha channel emulated with black and white (white = opacity 100 and black = opacity 0). Sometimes the emulated alpha channel file has only full black and full white frames, but I think some videos that I want to create will have complex alpha channel emulation with gray scales.

Is it possible to make with ffmpeg an vp8,vp9 -pix\_fmt yuva420p ready .webm movie?

**Tags:** ffmpeg, alpha, vp9


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## 1 answers

### Answer by username_1 on 2018-04-09. Score: 3 | Accepted answer

The alphaextract/alphamerge filters are meant for this.
Since your alpha reference is already greyscale, we only need the alphamerge filter
ffmpeg -i main.mp4 -i alpha.mp4 -filter_complex [0][1]alphamerge,format=yuva420p -c:v libvpx -auto-alt-ref 0 out.webm

> **Comments:**
> **username_0**: Wonderfull! A perfect result with b/w and complex greyscale alphaemulated movies:). Now i can relaxed wait that my Videoediting and Animating Software implement this automatically.  

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