FFMPEG store alpha to separated clip

ffmpeg -i interlacedMovieWithAlpha.mov -vf alphaextract,format=yuv420p -flags +ildct+ilme alpha.mp4

Flags are generic way of telling it that it is interlaced…

Simplistic way to check for alpha (RGBA)

mediainfo clipWithAlpha.mov | grep ': RGBA' && echo "has alpha"