chequerboard missing

Hi, I need some help !
When I upload my clip (a black silhouette of a man running on a transparent background) it appears on my account as totally black video ie. P5 didn't recognize my embedded alpha channel.

I know my file is ok on my end as I checked by importing it back into After Effects and the transparency around the man is there.

I used QT Animation 80% RGB+Alpha in the export of the clip.

Anybody experienced this before? Am I doing something wrong ? any advice appreciated.

Thanks guys !