Stream Resolutions Are Quality Maximums, Not Minimums

posted Dec 19, 2019
in Bloviation

From the "It's Obvious When I Say It, But..." department: I recently figured out to put something into words that has been bothering me for a while: We tend to treat stream resolutions as putting a minimum guarantee of quality on a stream. Thus, a "720P stream" must be lower in quality than a "1080P stream", which must be lower in quality than a "4K stream".

This is backwards. Stream resolution puts a maximum quality on a stream. For a given codec setting, the more bits you allocate to a stream, the better it will look, until eventually it gets to the point where there's no more quality to be had. A 720P stream will reach this point sooner than a 1080P stream, which will in turn reach it much sooner than a 4K stream.

However, prior to that point, what really matters more is the bandwidth of a stream. A "720P stream" pushing a megabyte/second will be higher in quality than a "4K stream" pushing 800kilobytes/second. It's completely possible to have a higher quality "lower resolution" stream.

You can see this in DVDs. The early ones were poorly encoded, and often had fewer bits since double-layer DVDs weren't widely-available and cheap yet. The later ones are much nicer, and with the double-layer, have a lot of bits. The result is a DVD stream that is pretty much maxed out, despite its lower resolution. Blu-rays have a larger nominal resolution, a superior codec, and the ability to throw about 5 times as many bits at a video stream... yet for all that, they aren't necessarily that much better. If I get up close to a Blu-ray stream on my TV, it clearly has a ways to go before it hits "maximum quality" for 1080P. It's certainly better, just not by as much as you'd think, because modern DVDs are already fairly high quality. Contrary to popular opinion, if you are a cinephile, there is still a place for distributing media to people in their homes, where you can casually allocate 40GB to a single movie for a quality experience.

Marketing takes advantage of this widespread misunderstanding. I tend to look askance at anyone claiming a "4K stream". Few companies are willing to pay to serve such streams properly, and even in 2019, few home Internet connections are strong enough to reliably stream what it would take to truly max out a 4K stream. I've seen many "4K streams" that are more accurately described as "fairly decent 1080P streams, finally".

 

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