Netflix offers 4K movies, but are they good enough to compete with the UHD Blu-ray you can find in a store? Well, no. Streaming will almost always look worse, but for some things it might not matter. Here’s the breakdown.
Streaming Compression Ruins Beautiful 4K Movies
Playing a 4K video from Netflix’s servers should be the same as playing it from a Blu-ray, right? Not exactly. While both videos will technically have a resolution of 3,840 pixels by 2,160 pixels, what’s in those pixels is determined by something called compression. To dramatically oversimplify a complex topic, compression lowers the file size of a video by tossing out redundant or unnecessary information. If a shot doesn’t change much from one frame to the next, modern compression can tell a video player to only update the pixels that do change, rather than redrawing everything.
Compression also reduces file sizes by reducing the quality of a picture, usually imperceptibly. An uncompressed 4K video would be over 5 terabytes of data per hour, which is way too much to put on a Blu-ray or even stream. Compressing the picture quality—by tossing out very minor pixel detail, for example—gets it down to a much more reasonable size. But “reasonable” can be very different depending on whether you’re streaming from Netflix or watching a disc.
4K Blu-rays can store up to 100GB of data, which is huge. It’s also around a tenth of the data cap Comcast imposes on its home internet service. If you had to download all of that for every movie and TV show—assuming your connection was fast enough to do so—you’d blow through your data cap in a matter of days. So, Netflix compresses your movies and shows a lot more than a Blu-ray would.
How much more? Well, to compare, we can look at the video’s bitrate, which basically means how many bits the video contains per second. Netflix doesn’t say exactly what the bitrate is for its 4K shows, but a help page recommends having at least an internet connection capable of streaming at least 25 megabits per second. Meanwhile, a Blu-ray “streams” (through your HDMI cable to your TV) at anywhere from 82 megabits per second to a whopping 128 megabits per second. That’s anywhere from 3-5x as fast as what Netflix recommends to watch its 4K movies.
The result is watching a show on Netflix will sometimes look a lot worse than if you were to watch those same shows on a Blu-ray. This is especially true of scenes with rain, snow, or confetti, which trip up compression algorithms more than usual. Some scenes—especially scenes with little motion and simple images, like say a cartoon—will look perfectly fine. But scenes with a lot of detail or movement can end up looking pixelated or choppy because compressing the show down to a streamable size throws out a lot of data.
So, You Should Always Buy the Blu-ray, Right? Not Necessarily
If you care about getting the best picture quality possible, then yes, the Blu-ray will almost always be the best version of the movie. However, it’s worth pointing out the obvious: for most people and a lot of shows, streaming 4K video is perfectly fine. Put simply, you don’t need a 4K HDR stream to enjoy Friends on Netflix. The visual quality on shows like that kind of isn’t the point.
There’s also some gray area when it comes to streaming if you meet the right circumstances. The average home broadband speed is getting higher, which might make higher quality 4K streaming video an option (though video providers still need to stream at higher speeds). Or if you use an app like Plex to host your own movies, you can get a lot more control over the streaming quality.
And then there’s the obvious caveat: Blu-rays are a lot more expensive than streaming. Not only do you have to buy a $20+ disc, but you have to own a relatively expensive Blu-ray player (or game console). Is that extra expense worth it to get some finer pixel quality from your movies? It might be! But if you’d rather save the money at the expense of some picture quality, skipping the disc probably won’t hurt your experience too much.
HDR Might Make Your Shows Look Better At a Low Bitrate Anyway
The 4K revolution isn’t coming to your living room alone. High-dynamic range (or HDR) is an even more important new technology that gives you brighter lights, darker blacks, and increases the range of colors your TV can display. Arguably, HDR is a much bigger innovation. 4K just gives you more pixels, but HDR changes what those pixels can be, for a more vivid, vibrant picture.
HDR has an interesting relationship with bitrate. Technically, HDR uses 10-bit color instead of 8-bit, which can add up to 20% to the bitrate of a movie. Sounds like it would be a lot more data to stream, right? However, compression changes the game here again. Since HDR movies can display more nuanced colors, the footage can be compressed further while still leaving in the same amount of detail. In some cases, the bitrate increase can be as low as zero.
More importantly, you’ll still be able to see more colors than you normally would. As far back as the first DVDs, most videos you’ve seen have been capable of displaying around 16.7 million colors. HDR is capable of displaying over a billion. Even if streaming video compresses some of that detail, you will notice when your eyes are seeing shades of colors you’ve never seen from your TV before.
So, yes, watching something on Netflix won’t be quite as high quality as watching it on a Blu-ray. At the same time, if its an HDR movie or show, it will look a heck of a lot better than regular HD, and parts of it still might be crisp enough that you won’t notice the difference.
Overall, if you’re a stickler for video quality, you’ll still want to get the Blu-ray. It gives you more bandwidth and a higher quality source for your favorite movies. You’ll get the most out of it from blockbuster films with lots of detail and expensive effects, since a drama where two people sit in a room and talk doesn’t benefit as much much from a billion colors and four times the pixels you’re used to. You’ll probably be just fine with streaming—and 4K HDR streams are still better than the alternative—but there’s always room to improve.