Streaming Buzzwords-What Do They Mean?

Every technology area comes with its own set of often-repeated acronyms and phrases. Streaming media is no exception. Whether you are new to streaming or just looking at upgrading to leading-edge technology, you might wonder what those buzzwords are all about. Let’s take a look at a few of them.

• Adaptive bitrate (ABR) streaming. Have you ever watched a show on Netflix or Hulu and noticed the picture get a bit fuzzy for a few seconds, then snap back into sharp focus? You were seeing adaptive bitrate streaming in action. With ABR streaming, your playback device automatically detects your local bandwidth and playback capabilities every few seconds and, as needed, shifts to a video stream with a higher or lower bitrate and/or resolution (frame size). The video quality may change a bit, but the goal is to keep the audio quality constant and never pause the stream to “buffer.” Most of the live and on-demand content you see today starts as a single high-definition live stream or file, and is then converted into multiple streams or files at different resolutions for ABR streaming to each viewer, allowing every individual to receive the best possible quality video for his or her specific conditions.

• Codec. This mash-up of the words coder and decoder (or compressor and decompressor) describes the advanced compression logic used by an encoder (see below) to convert audio and video to much smaller streams or files for more efficient storage or network transmission. The same codec is then used later by a decoder to reverse that process as the content gets played on a user’s device. A simplistic analogy might be to think about how you would ship a typical beach ball across the world—you’d remove the unneeded parts (the air molecules), ship the deflated ball in a small package, and when you want to use the ball, you’d open the package and put air back in the ball. Codecs do something similar, giving encoder software the intelligence to remove the parts that aren’t needed until the content is played, and then telling a decoder how to restore the necessary parts during playback.

• Content delivery network (CDN). When you want to deliver your streaming media content to a large or broadly distributed (e.g., global) audience, using a CDN can be a great choice. They provide an efficient way to instantly copy small pieces of your streams or files from your web or media server (known as the origin server) out to dozens, hundreds, or thousands of edge servers around the world, each of which can then deliver to hundreds or thousands of end users. Sometimes referred to as caches or repeaters, those CDN edge servers are typically located closer to your content viewers than your origin server is, and thus deliver the content with lower latency and a higher quality of service.

• Encoder. A software application or physical device that compresses audio or video content using codecs (see above).

• HTML5. A new standard for the creation of web content. With the addition of the HTML5 Media Source Extensions, live and adaptive bitrate streaming of video can be accomplished in an HTML5-compliant web browser without the need for a third-party plug-in, such as Flash or Silverlight. The intent is that ABR video will someday play natively across all browsers, including those on mobile devices. Unfortunately, native codec support is inconsistent across mainstream browsers, so you may need to publish your content using two or more streaming formats to reach all your viewers. Fortunately, some HTML5-compatible media players support multiple codecs plus legacy Flash playback, allowing any-screen reach using a single player.

• MPEG-DASH. There are many different streaming formats. Traditional streaming uses protocols such as RTSP and RTMP that require opening up specific network ports on firewalls and computers. More-recent adaptive formats are based on the HTTP protocol (the same protocol used with standard web pages, requiring no special port configuration). These formats include Microsoft Smooth Streaming, Apple HLS, and Adobe HDS. Some of the best aspects of those and other formats were combined to create MPEG Dynamic Adaptive Streaming over HTTP (MPEG-DASH), the first vendor-independent adaptive streaming format. MPEG-DASH is now an international standard that works across most modern browsers, game consoles, streaming devices, and smart TVs.

• Network DVR. DVR stands for digital video recorder, so think of the great features you get with a TiVo or a modern cable box: the ability to pause a live stream, go back to the start of in-progress show, do your own instant replay, and then return to the live stream. Most traditional set-top boxes that provide this rely on a large hard drive to store the content, but taking up a lot of storage space with video is infeasible on many desktops and mobile devices. Network DVR (or nDVR) stores all the content on a media server or content delivery network (CDN) somewhere upstream of the viewers, and allows those viewers to access it instantly across their network connections on any device with a compatible streaming media player.

• Packaging. As mentioned under MPEG-DASH, there are many streaming formats out there. Fortunately, most of them use the same video and audio codecs (H.264 and AAC, respectively), so you don’t usually have to encode your content using multiple codecs. Instead, you just need to package the H.264 and AAC content a bit differently to reach some players and devices, whether they use RSTP, RTMP, HLS, HDS, Smooth Streaming, or DASH. Think of writing a letter and sending it to many people. You don’t need to print each copy of the letter in a different font; you just need to photocopy one letter and then put each copy in envelopes (packages) that each have slightly different mailing information on them.

• Transcoding. Originally, transcoding meant the process of re-encoding digital content from one set of codecs to another. These days it also encompasses the ideas of transrating (in which you re-encode from a high bitrate to one or more lower bitrates) and trans-sizing (in which you re-encode from a high resolution to one or more lower resolutions). When creating ABR content, the transcoding process sometimes includes changing codecs, but almost always involves both transrating and trans-sizing content.

• Transmuxing. Another term for (re)packaging. See the Packaging section above.

For more streaming terms and their definitions, please see the full Wowza Media Systems Glossary.