DVD/Bluray typically use MPEG2- for the sake of discussion this is 'uncompressed' because studios don't make raw video data available. Many consumer videos are transcoded into a more compact MP4 format - of course you need a specialized device or a PC to watch MP4. Most media players nowadays can support mp4 decoding, however. It's not the same quality as mpeg2, but passable to the casual viewing audience, mp4 uses predictive motion encoding, spatial and temporal compression, and reduced chroma sampling sometimes. Modern video streaming services now all probably use moderate-complexity mpeg4 encoding, resulting in a lower bandwidth. (movies rented from Apple, amazon, netflix, etc). A 1.6 Gbyte mp4 file is decent 720p depending on the scene contents and length of the video, at a fixed bitrate.

edit: and it's worth noting that these small video files will typically strip the multi-channel audio and favor a remixed stereo-only sound track. saves more bytes.

edit: kudos to poster below for clarifying my half-baked explanation.