Any AI-generated video (up to a minute) created inside any of your campaigns is considered a credit. Pre-recorded uploaded videos that are used as "Elevator Pitch" or "Transitions" are not calculated as credits. Only the audio-visual generations are calculated in the credit counts. For example: If you generated anything up to one minute video it will be counted as a single credit.
For example, if you upload a list of 1,000 different emails, it will require 1,000 credits. However, instead of thinking about the credits spent, think about the responses and ROI these credits will bring to you. :-)
You can always top up your account with credits at anytime.