Originally Posted by CaioTheBrain
Netflix uses a headroom of 40%. Therefore, a 7.3 Mbps connection is needed to ensure the 5184 kbps bitrate streaming (4800 for the 1080p video and 384 for the 6-channel audio).
Exactly. Netflix rounds it up to 8 Mbps but it's highly dependent upon what you're watching. A dialog-driven title with little action isn't going to come near to averaging 4.8 Mbps and its 1080p encode can probably be streamed by someone with significantly less available bandwidth.
Before adaptive bit-rate streaming (ABS), the players would test available bandwidth and choose a video encode accordingly. Now it's completely dynamic. I think that the players will perform a test to decide where to start, but they keep stepping up through the available video encodes until they get to the highest bit rate one with which they can keep their buffers full under current conditions; if the buffer starts emptying out they'll step down to a lower bit rate/lower picture quality encode before they run out of content to play, but they'll keep trying to step back up to better quality video.
Netflix titles have standard-def video encodes at 235-, 375-, 560-, 750-, 1050- and 1750-Kbps; HD titles have 720p encodes at 2350- and 3600-Kbps and (usually) a 1080p one at 4800-Kbps. Add to that 192 Kbps for stereo sound or 384 Kbps for 5.1 channel DD+ (when available). There's a special 64 Kbps stereo sound encode which I think is only available for PCs and portable devices.