Sure, you can use one of the converters available on GOTD from time to time, or your choice of free or paid software, but the goal here is the simplest way to watch a movie from a Blu-ray disc, with subtitles etc., on a Kindle tablet. Yes, the 10" Kindle tablet is the only one with a 1080P display, but it works fine on a 7" or 8" model too. Yes, you can make the files smaller by re-encoding the video, but the philosophy here is "Why bother"? You can pull the microSD card you're using in the Kindle, and after re-formatting, copy the movie there, but it's easier, faster, and more flexible to use a USB stick.
TO start with you'll need to get the Blu-ray on your hard drive -- how you choose to do that is up to you, but apps like DVDFab's Passkey generally work fine. In addition to that software you'll of course need a Blu-ray drive, internal or external, for your PC/laptop. And you'll need to know the playlist that's determined and used by an app like Passkey when it decrypts & copies the Blu-ray to disk [Passkey will show you the playlist number in a pop-up message, or in win10, a notification].
The reason you need the playlist is that you'll open it in a free app called tsMuxer. Running the included tsMuxerGUI.exe, click the Add button, then browse or navigate to the Blu-ray folder's BMDV\Playlist\ folder, selecting the playlist needed from among the hundreds of choices [the other playlists are for a combo of menus, special features, & fakes designed as DRM]. Once you open the disc you'll see a list of the included streams -- you can remove those you don't want/need, and when you click on the audio track you want to use, you can check the box to only include the more basic version, e.g. Downconvert DTS-HD to DTS. Under Output choosing Blu-ray folder may be the most flexible, since you can use that for Blu-ray players on your PC/laptop too, but the .m2ts file in BMDV\Stream\ is the only thing the Kindle will play.
Once you click the Start Muxing button it'll simply copy the content from the original folder on your hard drive into a new folder -- it takes as long as it takes to copy the files, as there's no conversions going on. tsMuxer will copy the movie, the audio & subtitles you select, and the chapters, and the movie will be in a single file, rather than the several .m2ts files often used on a Blu-ray disc. That saves you from creating a playlist for the player, or playing the files manually one by one.
videohelp[.]com/software/tsMuxeR
Next format a USB stick [that's big enough to hold the movie] as exfat -- Kindles only read FAT32 or exfat, & FAT32 won't let you use large files like the .m2ts movie -- & copy the Blu-ray folder tsMuxer created, or just the .m2ts file to the USB stick. There are reports posted that Kindles may not work with some USB sticks -- this one is known to work: amazon[.]com/ADATA-UV128-Retractable-Capless-AUV128-32G-RBE/dp/B00B7JM0WO/ref=sr_1_16?ie=UTF8&qid=1542751861&sr=8-16&keywords=adata%2Busb%2B3%2Bstick&th=1
TO connect the USB stick to a kindle you need an OTG cable [they're cheap] --
amazon[.]com/s/ref=sr_st_price-asc-rank?keywords=otg+cable&fst=as%3Aon&rh=n%3A172282%2Ck%3Aotg+cable&qid=1542749629&sort=price-asc-rank
And to play the movie you can use VLC for Kindle --
amazon[.]com/VLC-Mobile-Team-for-Fire/dp/B00U65KQMQ
When you connect the USB stick the Kindle should show you a notification -- if it doesn't, unplug the USB stick & try again [I've only had that happen once]. When you start VLC it may ask if you want to add the USB Stick [media] to your library -- when it's added to the library VLC should find the .m2ts file and show it's available to play. If it doesn't, browse or navigate to the file on the USB stick in VLC. You can customize the settings, but everything works for me at their defaults.
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Notes: Copying a Blu-ray disc to the hard drive will take a while, but you'd have to spend that time regardless the methods used. Using tsMuxer to copy the files is faster than any sort of conversion. Copying the files to a USB stick takes time, but so does copying the files anywhere else -- you should be able to use any sort of USB drive, and some are faster to copy to than others, though it's recommended to use a powered hub for external hard drives & SSDs. It can be a slight hassle having a USB stick hanging from a short OTG cable -- they have OTG adapters, so no cable dangling, or I picked one of these up for around $10 on sale:
amazon[.]com/Unitek-Docking-Ethernet-Smartphone-Ultrabook/dp/B00Z6DJACU/ref=sr_1_13?ie=UTF8&qid=1542752894&sr=8-13&keywords=unitek+dock