Webm capture corrupted by enabled alpha in THREE.js

[vaneenige]

Capturing with format set to Webm causes the file to be corrupt on export when the alpha of the canvas is set to true.

With the latest version THREE.js (v82) and THREE.WebGLRenderer({ alpha: false }) it works totally fine! With alpha set to true and format set to png the export does actually work.

[spite]

Corrupt as in can't be played, or as in it plays but there are glitches and artifacts?

WebM doesn't support transparency, I don't think the conversion from alpha-enabled canvas to webm frame is defined, so the glitchy playback would be the expected result.

Related: https://github.com/spite/ccapture.js/issues/18

[vaneenige]

Corrupt as in can't be played. The problem wasn't directly obvious to me but when I saw the PNG working with transparency I knew it had to do with the alpha. Might this be added to the documentation to let the user know it wouldn't work?

[devotionsolutions]

Same here. I'm trying to capture an animation created with Babylon.js and using an alpha channel background. The result is a corrupted webm file.

[mrdoob]

WebM doesn't support transparency

Are you sure?

[spite]

May be it does now. What's for sure is that the library that I'm using to encode WebPs into a WebM doesn't support it -and it doesn't look like it will: https://github.com/antimatter15/whammy/issues/7

Previously if you tried to save a video with transparent background, the background would be solid white, or have glitches. I don't know what's changed to make the videos not playable.

I'm still looking into the issue, may be I'll try another encoder (like https://github.com/Kagami/webm.js)

[Simran-B]

WebM supported an alpha channel mid 2013 already: https://developers.google.com/web/updates/2013/07/Alpha-transparency-in-Chrome-video

[bmarotta]

People who still have this problem should try the library: https://github.com/thenickdude/webm-writer-js