A video Content Delivery Network (CDN) is a global network of servers that stores local copies of video files, which increases the file delivery speed to nearby users. This helps scale your service and distribute high-quality video to more people.
For example, let’s say a user in Germany wants to view a video that is hosted in the United States. Normally, the video would be very slow to load. But if you use a CDN, the CDN chooses a delivery route and caches the video to a server in or near their location in Germany so the video can load faster. Since this happens behind the scenes, the user has a positive viewing experience, regardless of where they are.
In this article, we’ll cover:
- How does a Video CDN work?
- List of popular Video CDNs
- Why should you use CDNs? Benefits & business case
- Examples of CDNs in action
- How to use CDNs for video delivery: Static-origin vs dynamic-origin
How does a Video CDN work?
A Content Delivery Network (CDN), sometimes referred to as a content distribution network, is a system of interconnected servers located across the globe. These servers use geographical proximity as the criteria for caching content (i.e. segmented video files).
When a user requests content from their device—for example, by clicking a video play button—the request is routed to the closest server in the content delivery network. Locations that store cached video content are known as points of presence (PoPs).
If this is the first request for the video segment to that CDN server, the server will forward the request to the origin server where the original file is stored. The origin will respond to the CDN server with the requested file and in addition to delivering the file to the viewer, the CDN server will cache a copy of that file locally. When future viewers request the same file, the origin server is bypassed and the video is served immediately from the local CDN server.
CDN terms and definitions
Let’s review some terms that are often associated with CDNs:
- Cache: When a CDN keeps a copy of data. A “cache-hit” is when a CDN retrieves content from the cache instead of the origin server. A “cache-miss” is the opposite—when a CDN fails to retrieve content from the cache and has to retrieve it from the origin server.
- Video Origin: The server location where the original file is hosted.
- Edge: The server that is geographically closest to the user.
Points-of-Presence (PoPs): Server locations that store cached video content.
This image shows how each region has a CDN PoP, which contains cached files from the origin server
List of popular video CDNs
Popular CDN options include:
- Akamai
- Fastly
- Cloudflare
- Google Cloud CDN
- Limelight
- Level3
- CloudFront
- StackPath
In addition to this list, there are several other CDNs to choose from. Read more on G2 about CDN providers, along with customer reviews.
Mux Video uses a multi-cdn delivery architecture to ensure your video content gets delivered to every viewer as quickly as possible, even when a single CDN is experiencing an outage.
Why should you use CDNs? Benefits & business case
CDNs and business benefits go hand in hand, including lower costs, a better user experience, and improved performance and reliability. Here are the top three benefits to using a CDN.
1. Lower costs
Having a CDN PoP between the viewer and the video origin reduces the number of requests to your origin, which lowers compute costs. It also reduces the amount of data that is egressed from the origin location, leading to lower network egress costs. Finally, delivering video with CDNs reduces bandwidth costs because the content doesn’t have to travel as far.
2. Positive viewer experience
Users don’t need to wait more than a couple hundred milliseconds for a video to start playing when pulled from a cache. When users don’t experience interruptions, they are more likely to stay on a platform or website, increasing important metrics like video engagement and watch time.
3. Uptime and reliability
CDNs have traffic capacity that exceeds most normal enterprise network capabilities. Where a self-hosted video may be unavailable due to unexpected traffic peaks, CDNs are more distributed and remain stable during peak traffic times.
Examples of CDNs in action
Many popular media platforms use CDNs to optimize their user experience. Here are some real-life examples of CDNs in action:
Netflix Open Connect
The video streaming giant, Netflix, is very dependent on CDN architectures so they decided to build their own CDN. The company launched Netflix Open Connect in 2011. According to this Netflix blog post, “close to 90% of [Netflix] traffic is delivered via direct connections between Open Connect and the residential Internet Service Providers (ISPs),” with connections localized to the regional point of interconnection that is closest to the person watching the video stream.
Mux redundant streams
Mux not only supports automatic CDN switching for on the backend delivery side, but also HLS redundant streams. With HLS redundant streams, the video player has knowledge about more than 1 CDN at playback time. If one CDN is failing the player knows how to automatically switch to a backup CDN.
How to use a CDN for video delivery: Static-origin vs. dynamic-origin
Adding a CDN to your video delivery pipeline depends on your video origin—the location where your original video file lives. There are two types of origin deployments: static and dynamic.
Static-origin deployments
Static-origin deployments generate a half-dozen video encodings at various bitrates/resolutions, a HTTP Live Streaming (HLS) rendition manifest for each encoding, and an HLS master manifest to link them all. This also works for serving static encodings like MP4 files. Place the files in an S3 bucket and serve it from Amazon CloudFront or any other file-based CDN, and you're mostly done. This is the simplest option.
This image shows how static-origin deployments work at a high level.
Dynamic-origin deployments
Dynamic-origin deployments have increased in popularity because they offer additional capabilities like audience-adaptive rendition selection and Just-in-Time (JIT) transcoding. With a dynamic origin, video playback requests from individual users can be routed to different CDNs and include different encoding renditions depending on where the user is located, the device they're using, and the video content attributes. These decisions are typically made by the origin at the start of each playback. They are latency-sensitive and factor greatly into the time-to-first-frame and exit-before-video-start performance metrics.
Caching content at the CDN is much more challenging for dynamic origins. For video delivered using HTTP Live Streaming (HLS), which is currently the most popular bandwidth-adaptive protocol, the caching of manifests can present a hurdle. The master manifest is often not cacheable and must be served from the dynamic-origin, and can contain CDN-specific URLs for the set of encodings appropriate for the source content or device. Rendition manifests can often be cached on a CDN; however, for live content, the rendition manifests expire in mere seconds and must be retrieved again from the origin. The video segments, which make up the bulk of the bytes served, are highly cacheable and don't present much difficulty. This mixture of cacheable and non-cacheable resources greatly increases complexity.
This image shows how dynamic-origin deployments work at a high level. These deployments are much more complex.
Built-in CDN support with Mux Video
Mux ensures that every customer receives the benefits of a CDN without them having to individually negotiate terms with CDN providers. Mux Video automatically leverages multiple CDNs, selecting the best option for every video view based on real-time network conditions. Mux ensures secure video delivery and is integrated with CDN systems to monitor delivery usage and performance.
Learn more about Multi-CDN support in Mux.