As well as free, high-quality stock photos available for download on Pixabay, you can also download high-quality video from Pixabay too. This was perfect for me when I was creating a video on Camtasia. I could search for the video clip I wanted (a forest in my case) and download an MP4 to put into my project.
All videos are free for commercial use and no attribution required. This is a really easy way to create professional-looking content on a budget.