Hey !
This is a windows ONLY bug. @diff-arch tested everything on Mac, and it works perfectly.
The rhino “animate function” is supposed to be able to export : bmp, jpg, png, tga.
So does the Grasshopper animation function. Except, you got it, it doesn’t 
When you export images from the animate function in Grasshopper (windows), even the DEFAULT “.bmp” format for the frame isn’t supported by many softwares.
When changed to “.png”, any software can open it.
This is a know and very old bug, so are my hopes vain in asking for a fix? 
On mac, again, all of this works properly.
@diff-arch and I are about to release a small plugin that allows user to make plenty of conversions between different file formats (gif/images/videos). But the FFmpeg framework (that we use) doesn’t recognise the bmp and jpg formats created by the animate function inside on Grasshopper windows.
An update on this would be appreciated !
@DavidRutten @wim ?
Thanks
Antoine
_
edit: If I save manually all my images from Rhino (ViewCaptureToFile), any formats are totally ok to be opened in any software. So the problem really lies in the animate function.