If you’ve ever watched a movie on Netflix, YouTube, or some other streaming service, you might notice that any time there’s a rainy scene, the video quality completely falls apart. Even if you’re streaming over the best internet connection, the video will look like crap. This happens because all video streams are compressed, and particles like rain, snow, and confetti completely destroy compressed streams.
How Modern Video Is Compressed to Fit Bitrate Limitations
To understand why rain and other particles can mess up a video quality, we need to understand how bitrate works. A video’s bitrate is, to oversimplify, the amount of data that a video can pass through, measured in bits per second. You can think of it like how wide a water pipe is. The smaller the pipe, the less water you can push through at a time. The wider the pipe, the more water you can let through. Videos are similar: the higher the bitrate, the more data a video can display per second, which means more detail and better picture clarity.
In the world of HD and now 4K television, that limitation can become a problem. Most video you see is compressed in some way. If you were to watch a completely uncompressed HD video, it would have a bitrate of 2.98 gigabits per second. 4K video is even worse, with an uncompressed bitrate of 1.67 terabytes per second. Not bits. Bytes. That’s more data than the fastest internet connection in the world can handle.
Fortunately, modern compression does a decent job of preserving video quality, at least to a point. A standard Blu-Ray outputs at up to 40Mbps, and a 4K Blu-ray outputs at up to 108Mbps. The HDMI cables between your Blu-Ray player and your TV can transmit up to 18Gbps, so there’s more than enough room to handle all that data.
The difference between uncompressed video bitrate and the bitrate on your Blu-Ray discs is huge, but you probably won’t be able to tell. Uncompressed video contains a ton of detail that the human eye usually won’t notice, so a good chunk of that can be tossed. Additionally, inter-frame compression can dramatically reduce a file size by tossing out data when parts of an image stay the same between frames.
This shot can be compressed a lot since there’s very little movement or change between each frame.
Take the clip above of Luke Cage from The Defenders. In this brief shot, Luke tilts his head slightly to the right, and a cop stands up on the side, but for the most part the frame doesn’t change. The bars in the back are almost perfectly still, and even Luke’s body doesn’t shift dramatically. Inter-frame compression can tell a video to simply keep drawing the same background every frame, or to just shift some of the pixels in the foreground around, rather than redrawing every single pixel from scratch thirty times per second. This type of compression can make huge cuts in an otherwise massive video file size. Without this compression, everything from your internet connection to a basic HDMI cable wouldn’t have the capacity to transfer that much data.
That inter-frame compression runs into a problem with things like rain and confetti, though. Instead of a mostly static background, rain fall fills the entire frame with tiny details that need to be moved or redrawn every frame. Each rain drop takes up valuable bits that could be spent on a character’s face. The more little details there are moving around in a scene, the fewer bits there are to go around for everything, and video quality drops.
Streaming Online Puts a Massive Drag on Your Bitrate
If rain is such a problem, why don’t you notice this when you’re watching a Blu-Ray disc? The answer lies in the available bitrate. While Blu-Ray discs may undergo a massive amount of compression, they still have a high enough bitrate to render all those rain drops and pieces of confetti. In fact, if a scene were particularly busy or chaotic enough, you might notice some degradation in picture quality, but you’ll have to squint for it.
Streaming over the internet, on the other hand, just can’t keep up. The average internet speed in the United States is around 18Mbps, which is less than half the bandwidth required for a Blu-Ray disc—plus that bandwidth has to be shared by all devices on your network. Worse yet, a company like Netflix can only serve so much data at once, even if you have a fast enough internet connection to handle it. Netflix already accounts for a huge chunk of internet traffic on the internet. Streaming full Blu-Ray quality HD streams with the same picture quality of a disc would be unfeasible.
According to Netflix’s help site, the company recommends at least 5Mbps for HD video and 25Mbps for 4K streaming. This is very obviously a far lower bitrate than the Blu-Ray player in your living can handle. And remember, that Blu-Ray video is already pretty compressed. So, when Netflix decides to limit a stream’s bitrate even more, you’re going to start losing picture quality.
For basic, conversational scenes, this isn’t that big of a deal unless you’re the kind of person who gets really obsessed with picture quality. However, rainy scenes put more demand on an already strained bitrate. It’s like trying to hook a garden hose up to a fire hydrant. The capacity just isn’t there.
Take a look at this scene from American Gods. I streamed this show over a Google Fiber connection, wired directly into my desktop. Despite having plenty of bandwidth between me and Starz, you can see that the rainy scene is as pixelated as an 8-bit video game. In fact, the problem gets worse when it cuts from the close up of Shadow in the beginning of the clip to the wide shot at the end, because there’s more rain, which means more detail, which means less bandwidth for anything else.
Now, here’s that same scene. However, this time we created a GIF from a local copy of this episode, instead of streaming it. Of course, what you’re viewing is a 650 pixel wide GIF of a 4K video, so you won’t be able to see the full effect, but even here you can see more detail. Since the local video doesn’t have to be compressed as much as it would if it were streaming online, there’s a much higher bitrate to work with.
In this second version, you can see more rain drops, you can see the people more clearly, and the colors are even more vivid with better contrast. The higher the bitrate a video has, the less of a problem it is when it starts raining or when someone throws confetti. On a technical level, rain and confetti will always cause a compression problem, but you won’t notice it nearly as much if you’re playing it from a disc or a file on your computer, instead of streaming it online.
Of course, the tradeoff may be worth it for you. Sites like Netflix, HBO, and Starz have a huge library of HD and 4K content that can be expensive to get somewhere else (assuming you even can). Besides, most scenes aren’t in the rain anyway. While a movie will never look as good from Netflix as it will on Blu-Ray, it can look good enough. If you’re a stickler for good-looking videos, though, you’ll probably want to stick with physical media or your own home media server.