Quote:
Originally Posted by
Apostate 
Well, from Wikipedia, the bit rate for over-the-air HDTV is about 19 Mb/s for 720p and 25 Mb/s for 1080i signal. Blu ray is 40 Mb/s (max for video). Since these two formats are ubiquitous, I reckon we can consider them as HD in the conventional sense.
You're talking about maximum bit rates for an OTA broadcast standard and a video disc format. (That broadcast standard is generally confined to MPEG-2, which can't be compared on a 1-to-1 bit rate basis to AVC or VC-1, which disc and streams are generally encoded in). You will not find an official definition of "High Definition" which includes any bit rate; it'd be silly since new encoding schemes which produce higher quality results at lower bit rates are constantly being developed. High Definition refers solely to resolution. The ATSC defined HD resolutions as being 1080x1920 and 720x1280, both of which Netflix and some other streaming video sources provide (though only a few provide 1080 res at this point).
We almost never see maximum bit rates used in HDTV. Local broadcasters usually get video from their networks encoded at very high bit rates to withstand being manipulated in studio without significant loss of PQ (sort of like using high precision numbers in computer program calculations). After doing what they need to with it (adding overlays, inserting commercial ads, etc) the stations re-encode at a bit rate of their choosing. (Fox encodes to broadcast rates at the network and its affiliates use a system to insert their content without re-encoding). In the past cable systems have further re-encoded broadcast material to even lower bit rates, though I don't know how common that is today, given higher bandwidth cable systems and Switched Digital Video (last time I checked, my system wasn't). Looking at the sizes of my TiVo recordings the bit rates used by Bravo, ABC, Fox, ESPN, A&E, CBS and HBO are all over the place, none higher than 13.8 Mbps (ESPN for live 720p) and as low as 9.2 Mbps (A&E for canned 720p). It all looks pretty decent. The encoding equipment that they use gets progressively better at making efficient use of bandwidth.
As for HD video disc bit rates, those vary a great deal as well. I see
Harry Potter and the Goblet of Fire was encoded at 12.8 Mbps and
Troy at 11.7 Mbps--both got 4.5 of 5 stars for video quality in their High-Def Digest reviews. I'm certain that there are titles encoded to BD at higher bit rates with terrible PQ. In short, bit rate does not equal picture quality.
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What's Netflix HD? 3.85 Mb/s did you say? Now Netflix may have much more efficient encoding etc., but still 3.85 Mb is much less than 19 Mb. I say this while admitting (and give credit) that Netflix HD look perfectly fine to my eyes.
Really, isn't how it looks to you what really matters? To my mind, HD denotes a certain degree of sharpness and ability to discern fine details which much of Netflix's video delivers. (See
this example of their 3.85 Mbps 1080p--looks pretty crisp to me. Could it be even crisper? No doubt. With the new encoding with eyeIO tech, 3.85 Mbps 1080p24 replaces 4.8 Mbps and 3 Mbps 720p replaces 3.6 Mbps). Not all of their encodes are as good as I'd like, but the same can be said for film on BD.
Edited by michaeltscott - 1/24/13 at 12:54pm