Anything that accepts a standard SD card will also support a micro-SD, you just need an adapter. Every single DVD player you find is going to be compatible with SD cards - we’ve yet to find one yet that isn’t. With USB, most DVD players will have a slot for them, but you may have to format your files first. Some DVD players will also allow you to connect in an aux cable too. Barely anyone uses actual DVDs anymore, so it makes sense to store a couple of movies on something like a 128GB flash drive (which will hold at least a dozen standard, 90-minute long movies). Just be careful that your little ones don’t tear them out if they’re holding a portable model.