Muxing

Never head of the muxing? You’re not alone. There’s plenty of people out there who’ve never heard of this important process. Some might even assume it’s a typo for mixing (it’s not). We assure you muxing is very real. It’s present in everyone one’s lives every single day.

While muxing can be used in a variety of ways, it plays an important role in video processing. We’ll define what muxing is. We’ll also take a look at how it works and how it’s used. We’ll also dive into the process of de-muxing and how it differs with muxing.

Muxing defined

The term “muxing” is an abbreviation for multiplexing. If you break down the term multiplexing into its Latin root words, you’ll find its meaning. The root -plex means woven together and the root multi- means many or much. So, when you combine these roots together, they create the definition of: weaving together many elements. The specific definition of multiplexing is the process of taking multiple inputs, packaging them together, and sending them over a single output line. A classic example of muxing comes from telecommunications. When there’s multiple calls being made on the same telephone wire, multiplexing is at work. A single wire is sending serval signals simultaniously.

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The process of multiplexing is extremely important in both video production and broadcasting. It allows for just one device to send multiple inputs over a single line. It’s a quick and efficient way to send multiple inputs out at once.

Muxing/multiplexing is present in a few different applications. This includes analog and digital broadcasting, telephony, telegraphy and video processing. For the purposes of this article, we’re going to focus on muxing’s role in video processing.

Here’s great breakdown of the muxing process. Video courtesy: Simple Put

How muxing works in video processing

In video processing, multiplexing combines video and audio inputs together. When we take a look at digital video processing, multiplexing combines metadata, and things like subtitles, and places these inputs into a single container. Containers come in a few forms, such as multiple media files like MP4, AVI, MOV, and WEBM. They all house multiple, individual inputs together. Think of them like a shipping box will a few items in it.

Here’s a good way to look at muxing in video processing. At the start of the process, you have numerous inputs you’re looking to combine. This would include things like video, audio, and subtitles. These are all inputs. So when you’re working in a video editing software and you’re going to save the file, you’re engaging in the process of muxing. When saving, you’re compressing all of the different inputs into an output container, like MOV or MP4. Essentially, these containers house the inputs. This allows us to sent files with all of the important inputs compiled together in one file.

De-muxing

Since in many regards the muxing process is the packaging stage, there’s also a need for a stage to unwrap the inputs after being packaged. Since muxing is the process of combining multiple inputs into a single singal, de-muxing naturally is the opposite process. De-muxing, aka Demultiplexing, is the process of separating a single output into its inputs. So, this process separates all the inputs muxed in the container file.

De-muxing in video processing

So imagine, after you mux all the inputs, like video and audio, together into a single container, like a MOV or MP4 file, you need to unpackage these elements to be able to have them played. So, whenever you play one of these files on your computer, your computer will de-mux them. Essentially, your computer will unwrap the container, take out all the individual inputs, and send them over to the correct places. So, your computer will take out the video output and send it over to your monitor so the video can be displayed. Additionally, it will take out the audio output and send it to your computer’s speakers so it can be played.

Video, audio, and even captions are all inputs vapable of being muxed

Type of multiplexing

There a types of multiplexing out there. In this section, we will discuss Frequency Division Multiplexing, Time Division Multiplexing, and Statistical Multiplexing.

Frequency Division Multiplexing (FDM)

Frequency-division multiplexing combines multiple electrical signals into a single medium. It does this by sending out signals to numerous frequency ranges over a medium. Traditional radio and television broadcasting use FDM. Cable telvesion is also know for implementeing FDM.

Here’s an example of how FDM works. Imagine you’re watching TV using an old traditional television. Your analog television only requires one cable to receive several channel signals simultaneously. As your television is receiving these signals, it’s up to you to tune the television to the channel signal you want to watch.

Time Division Multiplexing (TDM)

Time Division Multiplexing is a technique that essentially combines low-rate channels into one single high-rate channel. In Time Division Multiplexing, users are assigned digital signals once they’re placed into time slots. Ultimately, TDM allows users to receive signals within the same amount of time.

To help describe TDM better, imagine three fruit crates placed in a line on a conveyor belt. At the end of the conveyor belt are hungry customers all want apples. The manufacturer at the start of the line places three apples in each crate. The manufacture then sends the crates down to the customers. They receive each crate and get their apples at the same time.

Statistical Multiplexing (STDM)

TDM focuses on delivering the signals impartial to priority and need; this isn’t always practical. STDM analyzes each user’s need and priority and decides which user will determine how much time each user will get. So say, there are two users: users A and user B. User A has more data than user B. With TDM, both user A and user B would be allotted the same amount of time slots. With STDM, user A gets more time slots than user B. This is because user A has higher priority with the amount of data they own. Many see STDM more efficient than TDM because it’s able to prioritize based on need.

Muxing/multiplexing in summary

Muxing (Multiplexing) has a wide range of uses. The end goal of muxing is to share signals. Muxing combines inputs like video and audio. It then compresses these inputs into a container file. Your computer will de-mux the container when you open the file. After de-muxing, the computer sends the different inputs to the correct areas, so the media will be played correctly. It’s an efficient way of sending signals. Most of us engage with the muxing processes every day and don’t even know it. Now, you know what’s going on behind the scenes when you are saving one of your videos files as a MP4 of MOV. So, whenever you open up a MOV file or save a MP4, remember the processes of muxing and demuxing.