It's a copyright issue--the U.S. Copyright Office.
U.S. Copyright Office
I don't know that I've seen a law/regulation/court decision on this. One might argue that it's covered by the copyright fair use doctrine, 17 U.S.C. section 107.
Chapter 1 - Circular 92 | U.S. Copyright Office. See generally:
More Information on Fair Use | U.S. Copyright Office. The idea being, just as the U.S. Supreme Court, in the Sony Betamax case, authorized the personal time-shifting of content you had a right to, personal format-shifting of your own content also is a fair use.
The U.S. Copyright Office has a nifty, searchable database of fair-use court cases, which one can search by topic and court jurisdiction, and then read summaries of the resulting cases. (Wow!)
Search Cases | U.S. Copyright Office
In quickly looking through a search there, I found the recent (2017) Disney/VidAngel 9th Circuit Court of Appeals case, in which fair use was not found.
https://www.copyright.gov/fair-use/summaries/disney-vidangel-9thcir2017.pdf. Although I haven't followed up with the court's written decision itself, the Copyright Office summary of the court's decision states,
Further, the court noted that space-shifting-the act of shifting media from one platform to another by copying a protected work and transferring it to another electronic device-is not a fair use; case law "unanimously rejects" the argument that space-shifting is a fair use, especially because Defendant's "service is not personal and non-commercial space-shifting."
But the distinction noted there might be the differentiator for an individual consumer (as versus the commercial business in the Disney/VidAngel case) doing the space-shifting, where it indeed
is personal and non-commercial.
Just a couple of additional points. (1) If you are just doing this for your own use, it is unlikely that you would be made a target. (2) Interestingly, TiVo and Toshiba themselves seemingly felt that format-shifting is legal: I own a Toshiba Series 2 TiVo box which has a built-in DVD recorder/player, a major feature of which is to allow the consumer to burn non-copy-protected shows recorded by the TiVo box onto DVDs.