How does a video CDN actually work

Content Delivery Networks (CDNs) have become indispensable tools for swiftly and efficiently delivering content worldwide. In our previous article on CDNs, we explored the basics — what CDNs are, their historical evolution, and their primary function of optimizing content delivery to users globally.

In this article, we’ll delve deeper into the world of CDNs, covering the nuances of video-focused CDNs compared to traditional ones. We'll also explore the multi-CDN architecture (a sophisticated approach to content delivery that leverages the strengths of multiple CDN providers) and debunk common myths surrounding video CDNs.

What is a CDN and its core functionality?

At its core, a CDN is a distributed network of servers strategically placed across different geographical locations. Its primary goal is to deliver content to end-users with high availability and performance by reducing latency and mitigating network congestion. This is achieved by caching content close to the user, thus minimizing the distance data must travel.

Originally, CDNs were designed to serve static content, such as images, CSS files, and HTML pages. However, as the Internet evolved and video content became increasingly dominant, the need for specialized CDNs arose.

Video content poses unique challenges, such as large file sizes, varying network conditions, and demand for high-quality playback. This makes it essential to understand how video-focused CDNs differ from their traditional counterparts.

Multi-CDN architecture: what it is and how it works

As the demand for high-quality video streaming continues to grow, so does the complexity of delivering video content reliably and efficiently. A single CDN may struggle to handle peak traffic loads, geographic disparities, and network failures. This is where a multi-CDN architecture comes in.

A multi-CDN architecture involves integrating multiple CDNs from different providers into a single network. This approach offers several key benefits:

• Redundancy: If one CDN experiences an outage or performance degradation, traffic can be rerouted to another CDN, ensuring uninterrupted content delivery.
• Load balancing: By distributing traffic across multiple CDNs, a multi-CDN architecture can prevent any single CDN from becoming overwhelmed during peak usage times.
• Optimized delivery: Different CDNs may perform better in different regions. A multi-CDN setup allows you to select the best-performing CDN for each user, improving overall delivery speed and quality.
• Cost efficiency: By leveraging multiple CDNs, businesses can take advantage of competitive pricing and reduce costs associated with content delivery.

Implementing a multi-CDN strategy requires careful planning and monitoring to ensure optimal performance. There are tools and services available to automate the process of selecting the best CDN for a given user at any moment, making multi-CDN architecture a powerful solution for businesses that rely heavily on video content delivery.

Structure of traditional vs. video-based CDNs

To understand how video-focused CDNs differ from traditional ones, it's important to examine their underlying structures and how they handle content delivery.

Traditional CDN structure

A traditional CDN is designed to handle a wide range of content types, including images, documents, and software downloads. The typical structure of a traditional CDN can be broken down as follows:

• Origin server: The origin server stores the original content. When a user requests content not cached on the CDN, the request is forwarded to the origin server, which then delivers the content to the CDN.
• CDN edge servers: These servers are located at various points of presence (PoPs) around the world. When a user requests content, it’s delivered from the nearest CDN edge server, reducing latency and speeding up the delivery process.
• Caching: Content is cached on the CDN edge servers based on demand. Initially, content may be stored in a ‘cold’ state on the origin server but as it is requested more frequently, it becomes ‘warm’ and is cached closer to the end-user. This process is known as origination and is crucial for reducing load times and improving performance.

The structure of traditional CDNs make them highly effective for delivering static content but are not always optimized for video streaming’s unique demands.

Video-based CDN structure

Video CDNs are specifically designed to handle video content delivery challenges. Unlike traditional CDNs, where content is cached on-demand, video CDNs rely heavily on pre-caching and video player integration. A video CDN’s structure can be summarized as follows:

• Video origin server: Similar to traditional CDNs, video content originates from a central server. However, video content is typically divided into smaller segments (e.g., two-second chunks) to facilitate smooth streaming.
• Edge caching: Video CDNs prioritize caching content at edge servers close to the end-user. This is especially important for video streaming, where even minor delays can result in buffering and a poor user experience. Almost all video content is served directly from cache, minimizing the need for repeated requests to the origin server.
• Adaptive bitrates streaming (ABR): Video CDNs often use ABR to dynamically adjust video stream quality based on the user's network conditions. This ensures users receive the best possible quality without interruptions.

Essentially, while traditional CDNs are designed to handle a broad range of content, video-focused CDNs are tailored to the specific requirements of video delivery. This includes a greater emphasis on caching, video player integration, and support for adaptive streaming technologies.

Myth debunked: CDNs or more PoPs mean faster video loading

One of the most persistent myths in terms of video delivery is that simply using a CDN or having more PoPs will automatically make your videos load faster. While CDNs play a critical role in optimizing content delivery, they are not a silver bullet, especially when it comes to video content.

Understanding video chunking and load times

Video content is typically divided into small segments or chunks, usually around two seconds in length. When a user begins streaming a video, the player requests these segments sequentially. As long as the player can load each segment before the previous one finishes playing, the user will experience smooth playback with no buffering.

Given this, the key to short video loading times is delivering each video chunk in under two seconds. If the CDN can meet this requirement, the video will play smoothly regardless of the distance between the user and the CDN's PoPs.

The reality of PoPs and video delivery

Another common misconception is that more PoPs automatically lead to faster video delivery. While having more PoPs can reduce latency for certain types of content, video CDNs benefit more from strategically placed PoPs closer to the internet backbone, rather than sheer quantity.

Modern video CDNs focus on having fewer, more strategically placed PoPs optimized for high-speed, high-bandwidth video delivery. This approach ensures efficient video segment delivery, regardless of the user's location.

Additionally, advanced video CDNs offer customizable PoP configurations, allowing businesses to select the optimal number and locations of PoPs based on their specific needs and audience.

Key takeaways

As video continues to dominate internet traffic, understanding the differences between traditional and video-focused CDNs is crucial for businesses that rely on high-quality video delivery. While traditional CDNs are effective for a wide range of content, video-focused CDNs offer specialized features designed to meet unique video streaming challenges.

By understanding these distinctions and leveraging the right CDN strategies, video creators and businesses can deliver high-quality video content to their audiences efficiently and effectively. If this suits your business needs, you can get started with Kinescope’s private CDN, which uses an open-source public API and supports large traffic volumes.