I try to export from Motion PAL anamorphic to Animation codec, 'cause I need an Alpha Channel . The result is always an Animation Movie but 5:4 instead 16:9. In the specifications for Animation, I don't see the possibility to check 16:9.
First thing to understand is that SD (standard definition) PAL is always 720x576 which is just by the pixel count 4x3 aspect ratio.
How to we get the 16x9 aspect ratio images out of that without changing the pixel count. Simple, just define each pixel as NOT square and I can then create a 16x9 picture with a 4x3 pixel count = PAL SD anamorphic. The pixel count for PAL SD with SQUARE pixels is 1024x576.
Animation codec (or any codec for that matter) doesn't care if your pixels are square, anamorphic, round, triangle... A pixel for the codec is just a bunch of numbers. The only reason some codecs have the 16x9 option is to tell the software that uses it that it's pixels are supposed to be interpreted as anamorphic shaped.
So you can export from Motion as animation 720x576 and when you open this clip in FCP make sure to tell FCP that this clip is 16x9 and it will display it accordingly.
Hope all this makes some sense (if anybody disputes anything please correct me as I'm not a technician by trade)