I just got an LG external DVD drive (a model recommended in Linux forums) and it plays video DVDs on one Debian (buster) laptop but not my other one. The Debian installation is the same on both, buster and fully up-to-date. I have installed libdvd-pkg on both, as well as udftools and regionset. The DVD player works on my Lenovo Thinkpad T420s (which already had a working internal DVD drive), and it doesn't work on my Dell Latitude E7440 (which has no internal DVD drive).

Here's what happens on the Dell:
Data, audio, and unencrypted DVDs seem to work fine. When I insert a commercial (encrypted) video DVD, originally Nautilus would not show any external storage device. After installing udftools, Nautilus now shows the disc as '7.2GB storage device.' If I open the disc in VLC, the disc starts spinning, the window shows the disc title "TVSERIESNAME_...", and then that title disappears and the disc stops spinning. As if VLC gave up.

Output of lsusb on Dell:
Bus 003 Device 004: ID 04f3:0111 Elan Microelectronics Corp.
Bus 003 Device 003: ID 0a5c:5801 Broadcom Corp. BCM5880 Secure Applications Processor with fingerprint swipe sensor
Bus 003 Device 002: ID 8087:8000 Intel Corp.
Bus 003 Device 001: ID 1d6b:0002 Linux Foundation 2.0 root hub
Bus 002 Device 001: ID 1d6b:0003 Linux Foundation 3.0 root hub
Bus 001 Device 003: ID 0e8d:1887 MediaTek Inc.
Bus 001 Device 001: ID 1d6b:0002 Linux Foundation 2.0 root hub
(I left out a couple obviously irrelevant peripheral devices.)

Output of regionset:
regionset version 0.1 -- reads/sets region code on DVD drives
Current Region Code settings:
RPC Phase: II
type: SET
vendor resets available: 4
user controlled changes resets available: 4
drive plays discs from region(s): 1, mask=0xFE


output of dpkg -l | grep dvd
ii dvd+rw-tools 7.1-14 amd64 DVD+-RW/R tools
ii dvdauthor 0.7.2-1 amd64 create DVD-Video file system
ii libdvd-pkg 1.4.2-1-1 all DVD-Video playing library - installer
ii libdvdnav4:amd64 6.0.0-1 amd64 DVD navigation library
ii libdvdread4:amd64 6.0.1-1 amd64 library for reading DVDs

I'm in the US, and this is a region 1 DVD.

Any thoughts on what's going on? Other packages I must be missing to play/recognize encoded DVDs?

Two thoughts....

Maybe your USB is not backwards compatible?

Is the DVD drive USB2 or USB3; your Lenovo has a USB2 socket, is that where it works?

Small update: seems like Nautilus is not recognizing the DVD at all at the moment. Disks recognizes the 7.2 GB disc (properly as CD/DVD drive with the right model name) at /dev/sr0 but doesn't give an option to mount it.

Hi fatmac, as far as USB2/3, the drive works fine on the Dell as long as it doesn't have an encoded DVD in it. That to me says it's not a connectivity issue, but an encoding/decoding issue.

You probably mean "encrypted"?
You haven't mentioned libdvdcss anywhere in your thread. That's the library that does the decryption.

On Debian the package libdvdcss2 is installed via libdvd-pkg, which I have installed.

Well, fatmac, I have to revise what I said: it seems like it is connectivity and not just encryption that's the problem. I have only inconsistently been able to use the drive for non-encrypted discs on the Dell, and now most of the time Linux can't mount any disc. I tried this in another (2009) Dell workstation-laptop I have, running the same up-to-date Debian Buster, and that Dell also could not mount discs in the drive. Disks could see them, but mounting was not an option.

Just to make sure the drive wasn't failing, I checked again: the Thinkpad (2010) has no problem mounting discs or playing encrypted DVDs.

OK, so maybe I have a drive that's not compatible with Dell laptops. That seems impossible to me, but...what can I do? Try again with a different model of DVD drive? I hate to buy another if it's not going to work, either.

It could also be that the external enclosure the drive is mounted in is a POS. I have a universal connection set that I can use to connect any of the IDE or SATA devices and can test the device separate from the enclosure so that lets me see where the actual failure is. Sometimes it is the actual drive and sometimes it is the cable/electronics in the enclosure that has gone fubar.

For the price of DVD drives today it might be more economical to just buy a replacement. I have one thin DVD writer that I bought for use with my laptop several years ago and it has worked everywhere I tried it. It is only about 5" x 5" x 1/2" and IIRC it only cost about $80 - $90 then. Runs entirely off the USB with no power supply needed.