[Mitch Jc]"For a 3454mm(H) x 8640mm(W) led wall, what resolution should I render my animation in after effect? The supplier said 1280 * 720 which I doubt it and rendering will take a long time. "
Really, only your supplier or the technicians who will install or run the wall can answer these questions for you, but I'll give you a little background.
The resolution of an LED wall depends on its pixel pitch -- that is, the space between pixels.
If your wall has a pitch of 6.75 mm (which appears seamless if the viewers are far enough away), then it's certainly possible that the wall is 1280 px wide. However, the aspect ratio suggests that it's only 512 pixels high, not 720.
That said, you may need to deliver 1280x512 inside a 1280x720 raster.
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