I have few questions regarding development of desktop application and I can only access internet for first login where user will authenticate himself. I have an idea that I'll bring in the key used to encrypt videos from online server and save it to local db so key isn't in the code for anyone to inspect.
Is it a good method? As app will be running offline and I don't want anyone to access my videos.
I will have to decrypt one video and play it unless there is some method that decrypt and play on the fly like libmedia does it in android. I have no preference whether I have to develop it in Java or C#. Which language provides better obfuscation keeping in mind that I only need it for windows OS.
Thank you
It sounds like your are trying to develop a sort of light weight DRM solution - unfortunately, this is going to probably be lightweight in the protection it offers also.
For example, if you store the key in the DB it will still be relatively easy for someone to get to it using a regular DB viewing tool.
DRM is not really about making it impossible to copy content - more about making it hard enough to do that it is 'not worth it'.
Depending on how 'secret' or valuable your videos are your approach may be fine - i.e. you may make it enough work to find the key etc that uses won't bother. If your videos were regular studio produced content then they would probably not be happy with this level of protection.
If you do need stronger protection then regular DRM from MS, Adobe and Google etc is available through many of the standard video hosting providers (Brightcove, Ooyla, Kaltura etc) and the DRM they use will support offline playback, which I think is the requirement you have.
They will also all allow decryption and playback 'on the fly' - i.e. you don't have to decrypt the whole video before you play it back (in fact they would typically not do the whole video decryption first anyway as you would then have the whole content in clear stream making it easier to copy).