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I'm trying to convert a webm file that has a transparent background to an mp4 file. Mp4 doesn't have transparency so I'm trying to using this color: #D9DADB. How can I make this conversion happen with a single command in ffmpeg?

I've tried the following command and I seem to get a black background instead of a gray one: 

ffmpeg -f lavfi -i color=c=0xD9DADB -i 123.webm 123.mp4
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1 Answer 1

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The native VP8/9 decoders don't support transparency, so a) you'll have to force a decoder, b) the way to change transparent pixels is to overlay the video onto the color.

ffmpeg -c:v libvpx -i 123.webm -f lavfi -i color=c=0xD9DADB,format=rgb24
       -filter_complex "[1][0]scale2ref[bg][vid];[bg][vid]overlay=format=rgb:shortest=1,setsar=1"
       -pix_fmt yuv420p -c:a copy 123.mp4
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  • this is great - just 2 problems though. 1) the rendering doesn't stop - it can go well past the final frame. 2) the resolution is different than the original. I'm guessing its because of the pix_fmt argument? How can i set specific dimensions for the final image?
    – Parris
    Jan 29, 2019 at 20:58
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    1) corrected, 2) not because of that, also corrected
    – Gyan
    Jan 29, 2019 at 21:03
  • If your WebM isn't using VP8 but instead VP9, you need to replace -c:v libvpx with -c:v libvpx-vp9.
    – luckydonald
    Mar 14, 2022 at 15:26

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