Playing movies on the Pi

As usual, DRM ('Digital Rights Management') gets in the way of the honest user (the dishonest one just pays less for a 'pirate' version of the same movie, which comes without any 'Region Coding' and without any of the enforced viewing of 'FBI Warnings' or pre-movie 'adverts' and is thus arguably a more desirable choice than purchasing the 'real' thing)

For HD, full H.264 decode (and encode) is supported in the GPU, so UNENCRYPTED (i.e ripped or 'pirated') HD Blu-Ray movies (with AC3 5.1 sound) can be played back directly from a USB BD disc player by the Pi to a HDMI display (and even in glorious surround sound, if your display has a home cinema system fitted to it).

Even if you pay for the a VC-1 codec Licence (the format used for some BD disc's and much Internet HD TV), this does not allow playback of BD discs. Further, the complexity of the DRM means that the Pi may never be capable of 'directly' playing any commercial BD disc (decryption software does exist but is likely too slow, even on the quad-core Pi B2, to run in 'real time').

The 'work around' is make your Pi a DLNA 'client' and use a PC to 'decrypt' the BD disc. The PC then acts as a DLNA 'server' and sends the decrypted movie data stream to the Pi for display

For 'normal' (DVD) movies, you need the MPEG-2 codec Licence, which is available on payment of a (tiny) licence fee, however the same restriction applies - only UNENCRYPTED material can be played back directly from a DVD disc.

Normal DVD encryption is not too complex, so whilst the Pi GPU does not support DRM decoding, it is possible to decrypt using the CPU, although you may need the quad-core B2 to do so 'in real time'. Of course don't expect the Pi to be doing 'anything else' (such as USB i/o) at the same time - so most users will be forced to 'hack' their standard definition DVD movies (remove the DRM and, if necessary, convert the sound from 44.1kHz to 48kHz, and encode into AC-3 / DTS) before they can play them via the Pi.
In the educational field, all of this DRM nonsense may be regarded as an 'advantage', since it helps both teachers and students learn about 'Licence restrictions' (i.e. the fact that when you 'buy' a movie disc, what you are paying for is 'permission' to play it on a 'licenced' player in some specific 'region' of the world (the Pi is not a 'Licenced' player for any region) and for your own 'personal viewing' (and for sure not in the class room)).

Understanding how Licence restrictions are 'enforced' (via DRM) and how it is possible to overcome these restrictions (and thus become a 'criminal pirate', risking the FBI tracking you down and you being sentenced to 'up-to' 5 years in jail and 'up-to' $500,000 in fines) will be an education it itself :-)

Further, it might even lead to a class discussion on the whole issue of DRM, copyright violation and the definition of 'theft' (as the Movie Industry continues in it's attempts to 'equate' the copying of music/movies to the actual crime of physical theft). At the time of writing (early 2016) the Industry has been running adverts that attempt to link 'piracy' with the stealing of a handbag. Of course a closer 'analogy' to 'piracy' would be the photographing of the contents of the handbag (actually theft of the handbag would be equivalent to stealing a physical movie disc).

Hopefully, Teachers (at least in the UK) could educate students in how the crime of theft is defined ('depriving the owner of use') and perhaps start a discussion on how 'copyright violation' leads to 'loss' (or not). A good way of doing so might be to bring in a camera and 'make a copy' of something - such as one of the children's art class painting - and then discuss how the 'copyright owner' (the child who painted the picture) has 'experienced a loss' as a result of that action.

This could then be followed by a general discussion on how making life difficult for your paying customers - enforcing the viewing of 'FBI warnings' and accusations of 'piracy', preventing playback in 'unlicensed Regions' and padding the movie with adverts etc. might be 'counter productive' to your future sales (especially as the Region free 'pirate' product, without the enforced viewing of time-wasting 'warnings' and 'adverts', might actually be more attractive to the customer than the 'official' product)