This is the simple workflow I use to select elements in my videos and images. It's powerful when used correctly and can save a lot of time masking. This workflow can be combined with other workflows to achieve great results. I suggest expanding the mask a little bit before using the result (GrowMask and Mask Blur nodes in Comfy). There are many workflows here on CivitAI that use specific mask areas, which can be easily created using this workflow. It will produce three outputs: a video with the mask (black and white), a folder with the images of the mask (black and white), and a folder with the original video frames as images. This way, you can use the video directly in another workflow or load the image sequence in Comfy, A1111, or any other software you prefer to work with.