And Flash window inside a browser? Ew! Why would you buy that if the free stream was already available?
Exactly, like it or not they are /competing/ with the 'free, if not technically legal' resources that are not likely to go away or die.
The quality needs to be at least as high (DVD rip quality at minimum, often 1280xwhatever, even 'Full HD' 1900xwhatever in some cases).
The file containers need to be 'modern' (.mp4 and/or ogg/mkv) and should support being re-merged in to other containers.
Any kind of DRM (In cryptographic terms trying to treat Alice as Eve) will only hurt legitimate consumers, not those who aren't customers anyway.
The codecs should be some kind of standard, as mentioned elsewhere good royalty free ones include Dirac and Theora for video, and Vorbis or even Flac for audio. (Yeah, flac doesn't compress much; you can always transport the stream in a compressed format like 7z or xz (mostly the same thing).)
Also remember to let the consumer extend the official streams with extras; Fansubs/Jokesubs (including textual through full-frame overlay styles and even video-merging; yeah I can hope... I don't even know of a container that supports that yet.), cutlists for abridged/AMV modes.
You can even work it out so that someone buys a license for a fully dubbed work, but gets the raw on the day it's released, and then the subtitle and dub tracks later as extras. Or someone could buy 'backups sent in the mail' on DVD/whatever as an upgrade to the base package.
Not to mention all the other upgrades/upsells that could occur later. Limited/plus editions including posters, and all kinds of other things.