We imported a 3840x2160 AI file to use as a background in Ch. We had it scaled to 50% to fill the 1920x1080 video we wanted to create. The preview in Ch worked great, but when the Ch was pulled into AE it took forever to preview. It was just a 1 minute video, but when attempting to use Media Encoder to produce a video, it was going to take close to 4 whether coming from AE or directly from Ch. We knew that was too long, so we investigated. We removed the AI background from Ch and imported the same AI background directly into AE. This time. When the background was not coming from Ch (only characters this time), the encoding took under 6 minutes, which is what we expected. There seems to be some issue with the encoding from Ch or large background AI files. AE handles them fine. I hope this explained it well enough.