Transparent background turns black in videos

[shashi]

Transparency becomes black in videos.

One way to solve this is to use IM convert on push! to flatten the png. But a better way would of course be some mysterious command-line flag in ffmpeg which does this.

[jfsantos]

Don't you need to use a codec that supports transparency? According to this, adding -vcodec qtrle should work.

[shashi]

@jfsantos I want to support any format. But it's usually the case that you'd want transparent parts to be white, not black - if transparency is not supported.

[jfsantos]

I see (and agree completely with transparency being replaced by white).
I'll take a look and ask a friend who used to be an ffmpeg developer.