For splitting the data into train, validation and test sets, you have to make sure that the test set does not include e.g. some seconds before and some seconds after a test sample since then the model might not actually generalize to entirely new videos. In general, it might make sense to use the beginning for training, the middle for validation and the end for testing.
Inside the three datasets you will create individual training examples.
Those training examples you can likely shuffle.
You could e.g. read through this blog post:
https://medium.com/smileinnovation/training-neural-network-with-image-sequence-an-example-with-video-as-input-c3407f7a0b0f 2