The classic definition of a CDN, or content delivery network, is an aggregation of servers dishing out live streams, on-demand content and other files to end users on behalf of various clients. In broadcasting, typical clients range from small radio and television stations to larger broadcast networks and media conglomerates.
The CDN’s role in the broadcast space isn’t so much changing but evolving. The now-simple idea of distributing content to a desktop grows more complex by the year. The explosion of mobile streaming and the ever-expanding OTT universe is evidence alone.
Simply put, there are more formats to learn, varying bit rates to accommodate and more devices in the consumer space. But it’s clear that broadcasters have as much to gain by diversifying their streaming blueprint as they have to lose by standing pat. The good news is that CDNs have the tools, the knowledge and the relationships to help broadcasters evolve their platforms.
How effectively a broadcaster communicates its needs to a CDN will go a long way toward establishing and growing a successful streaming strategy. Multiformat streaming and bandwidth management are two key engineering aspects to understand for enhancing quality and reach, along with software tools to effectively realize the associated business opportunities.
There is an inherent value in understanding bandwidth management, and the techniques and technologies involved, when streaming in multiple formats to reach many devices.
The MPEG-4 AVC/H.264 video codec is the primary choice in streaming environments today. It is the most pervasive mainly because it excels at representing the video picture at an efficient bit rate. Some have claimed that similar codecs, such as WebM’s VP8, offer higher efficiency, as well as real-time processing and licensing advantages. Most agree that H.264 offers an edge in picture quality.
However, many devices have difficulty supporting less well-known codecs because either the required decoding software is not widely supported or decoding the video demands a faster CPU or specific graphic processor on the device. In broadcast-quality streaming, H.264 offers a comfortable middle ground between high efficiency and not taxing devices at the decoding stage.
The most appropriate bit rate used for a specific frame size is dependent on the efficiency of the codec, as well as the amount of motion, color and detail of the picture. We often measure NetFlix, Hulu, Vudu and other professional OTT delivery platforms to determine the appropriate high-end bit rate for the content in question.
With NetFlix, we’re used to seeing encoded bit rates of 3.5MB to 5MB for 1080p downloads; roughly 2.5MB to 3.5MB for 720p, and 1.5MB/s to 2.5MB/s for SD video. These bit rates are sufficient to reproduce the high motion and detail of a Hollywood blockbuster. A lower bit rate can be used if the content is of low motion, as in a talking head or presentation slides, without a noticeable degradation in image quality. In multiformat streaming, bit rates will also be determined by the efficiency of the video codec used within corresponding container files, or wrappers. An H.264 codec in a multiformat streaming scenario will have at least several different wrappers around it. Table 1 shows several wrappers and corresponding end devices.