Even though the title list code was copied from FFmpeg/libbluray,
I didn't check that mpv used 0-based title indexing.
$ mpv bd://1 --bluray-device=. --msg-level=bd=v
[bd] Opening bd://
[bd] List of available titles:
[bd] idx: 1 duration: 00:00:36 (playlist: 00000.mpls)
[bd] idx: 2 duration: 01:31:30 (playlist: 00001.mpls)
[bd] idx: 3 duration: 00:00:50 (playlist: 00003.mpls)
bd://1 actually opens idx 2 from the list, not 1.
bd://mpls/1 opens playlist 00001.mpls as expected.
With this commit:
$ mpv bd://1 --bluray-device=. --msg-level=bd=v
[bd] Opening bd://
[bd] List of available titles:
[bd] idx: 0 duration: 00:00:36 (playlist: 00000.mpls)
[bd] idx: 1 duration: 01:31:30 (playlist: 00001.mpls)
[bd] idx: 2 duration: 00:00:50 (playlist: 00003.mpls)
should play the expected idx 1.
fb6481ecb5