While you could build something there are other issues to consider.

1. That's not backup.

We don't get backup unless we stay in a state of backup when a system fails. So if you have your laptop and it fails, do you have 2 backup copies? Are these backups on the same machine or house?

-> Hey I accept most can't maintain off site backup but how about a copy in a waterproof container that is in a place that survives a fire in this location?

2. I worry about power use. This is why I used the NAS feature of my router. I added a simple USB powered drive and I had my first of a few backups plus a media server (my router does DLNA, etc.)

3. Transcoding on the fly is nice but why not just do that on your PC so to have it all good to go? That's what I do and my NAS+Router sits then under a few Watts. I think it came in at under 5 Watts on the Watt meter.

Bob