More knowledgable AE guys will be along shortly.
You may need to contact the technical wonk at the venue to find out what codecs their system prefers. And then ask if there is someone who can handle the conversion or even the rendering for you if you send them the AE project and associated media. Also consider researching production methods for sport venue signage; it's a big industry with lots of suppliers and producers doing specialized work for those display systems.
There may be an upper limit to how wide you can truly go in AE, I do not know. 17+ thousand pixels is a bit much.
You must get the specifications from the manufacture of the display. If all else fails I render an image sequence then convert that to the proper format with a third-party encoder.
Thanks Rick for your advice on this. Can I ask which third party encoder would work best on OS X.
>> You may need to contact the technical wonk at the venue to find out what codecs their system prefers. <<
You will first contact the people running the system or the people who made the system. You will ask them what codec they require. Then you will either ask them or ask us how to achieve that output.
But let's go back to this 17k-wide comp. You REALLY need a comp that size. Really? It's not just duplicated edge-to-edge? I've never heard of a sign system using that much space. They're always chunked out.
Thanks yes I'm trying to get in contact with my client but they are on the other side of the world. I've produced LEDs for all the UK football stadiums and as you say they normally duplicated but without having a direct contact I can only go off their specification. Cheers