I have burned a 1hr20min iMovie file onto a DVD-R disc using Titanium 11 on this late 2009 iMac with OSX v10.11.6 (El Capitan).The resulting files on the disk are BDMV and Gertificate.
Quicktime Player and Quicktime 7 will not play the file. I see a message that QT cannot read the file.
Neither does a Sony Blu-Ray player. I have also burned the iMovie file onto a similar DVD-R disc successfully which plays anywhere.Even the Sony.
However I would like to see the movie in full resolution on my TV and computer screen. On a Panasonic Blu-Ray player, DMR BS780 the disc plays perfectly.
In conversation with the shop salesman just now he infers that home made Blu-Ray discs may contain unacceptable files. I may take the machine back for an exchange.