Scalable Videos - What Are Your Best Practices

Hello Cp Adepts,

I am working on a project that targets both mobile and desktop devices. Let's limit mobile to iPad and desktop to modern browsers without Flash.

I have a bunch of MP4  instructional videos to publish. They can be either embedded or hosted on a server.

What's your best practice for using responsive, scalable content with an emphasis on scalable videos?

In other words, do you use multiple files and load them based on a detected screen size (similarly to responsive images for example via scrset attribute) or you use a single MP4 file?

I will appreciate your shared knowledge and expertise in this matter.