Convert PNGs to webm video with transparency

Question

I would like to use avconv to convert a series of PNG images to a WebM video, preserving transparency.

I understand that the pixel format used in the output video must support transparency. So I tried:

$ avconv -framerate 25 -f image2 -i frames/%03d.png -pix_fmt yuva420p output.webm

Unfortunately, avconv complains:

Incompatible pixel format 'yuva420p' for codec 'libvpx-vp9', auto-selecting format 'yuv420p'

Gyan · Accepted Answer · 2016-09-20 11:11:07Z

24

With VP8:

ffmpeg -framerate 25 -f image2 -i frames/%03d.png -c:v libvpx -pix_fmt yuva420p output.webm

Edit: Now, with VP9

ffmpeg -framerate 25 -f image2 -i frames/%03d.png -c:v libvpx-vp9 -pix_fmt yuva420p output.webm

answered Jan 24, 2016 at 11:04

Gyan

90.5k11 gold badges185 silver badges210 bronze badges

Thanks for the insight. Can't get it to work though, if I run your command, avconv complains that Specified pix_fmt is not supported. I am using avconv version 9.18-6:9.18-0ubuntu0.14.04.1, Copyright (c) 2000-2014
– sebastian
Commented Jan 25, 2016 at 12:15
Switch to a recent ffmpeg build and try.
– Gyan
Commented Jan 25, 2016 at 12:17
Still no luck. I am using avconv version 11.3-6:11.3-1~trusty now and still get Specified pix_fmt is not supported.
– sebastian
Commented Jan 25, 2016 at 12:32
In your answer (updated now) you wrote avconv instead of ffmpeg. So I used avconv, too. Working with ffmpeg, thanks!
– sebastian
Commented Jan 25, 2016 at 14:13
3

For anyone frustrated on Ubuntu LTS: VP9+alpha doesn't work on ffmpeg 2.8.x, you should get ffmpeg 3.x.
– Kagami Sascha Rosylight
Commented Sep 1, 2017 at 5:14

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cdlvcdlv · Accepted Answer · 2016-08-23 23:50:42Z

15

Since 2016-07-13, it's possible to encode VP9/webm videos with alpha channel (VP9a).

You only need a copy of ffmpeg compiled after that date. By the way, all you need to write is:

ffmpeg -i frames/%03d.png output.webm

FFmpeg understands png format and will set a default framerate of 25 fps and a yuva420p pixel format to the output.

answered Aug 23, 2016 at 23:32

cdlvcdlv

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4

I added -b:v 800k for an increased video bit rate to get a better image quality. The default wasn't good enough.
– Alex
Commented Jan 28, 2018 at 21:55
Doesn't work for me. ffmpeg 4.3.2, video doesn't transparent.
– JavaRunner
Commented Mar 27, 2021 at 3:44

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mosis · Accepted Answer · 2018-07-02 21:39:32Z

1

You can also convert a video wich allready contains an alpha channel to a webm video with transparency with this command:

ffmpeg -i myVideoWithAlphaChannel.mov -c:v libvpx -vf format=rgba myVideoWithAlphaChannel.mov.webm

The format of myVideoWithAlphaChannel.mov (generated with Blender3D) is:

With as Ouputs:

answered Jul 2, 2018 at 21:39

mosis

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3 Answers 3