There is a lot that goes on behind every video stream. To stream your videos seamlessly, video streaming protocols play a huge role. They break the video into smaller chunks and send it to the viewer. Depending on your requirements and end goals there are several protocols available. One of these is MPEG-DASH, which is widely used to stream videos online.
In this article, I’d shed more light on what MPEG-DASH is, how it works, and also how it compares to HLS, another streaming protocol.
What is MPEG-DASH?
MPEG-DASH is a streaming method. DASH stands for “Dynamic Adaptive Streaming over HTTP.” Because it is based on HTTP, any origin server can be set up to serve MPEG-DASH streams.
MPEG-DASH is similar to HTTP Live Streaming (HLS), another streaming protocol, that breaks videos down into smaller chunks and encodes those chunks at different quality levels. This makes it possible to stream videos at different quality levels and to switch in the middle of a video from one quality level to another one.
How streaming over HTTP came into existence?
Did you know streaming over HTTP wasn’t even a thing until iPhone 3GS came into existence? Up until then, video streaming happened over RTMP and required the Adobe Flash plugin for playback. Steve Jobs was determined to kill Adobe Flash. He vouched for open web standards to take charge of video streaming on web browsers and mobile devices. The industry-backed him and hailed him a savior. Nobody wanted to rest the faith of the entire video streaming industry on the shoulders of one corporate.
The death of Adobe Flash
To begin with, there were too many problems with Flash. It was proprietary. While the Adobe Flash plugin was compatible with most web browsers of that time, creating Flash content required web developers to buy costly software licenses from Adobe. Flash plugin was a security nightmare even when it was updated fifteen times a month. Setting up a dedicated server for RTMP streaming was another hassle and wasn’t exactly cheap.
Firewalls would disallow traffic over port 1935 essential to receive content from RTMP servers. Firewalls weren’t a problem for content over HTTP since port 80 is always set to allow.
Further, Adobe Flash was too resource-heavy for battery-operated devices. It was simply impractical to bring Flash to mobile devices when web standards were constantly evolving. There is a reason death of flash is often regarded as the rebirth of the web we know today.
The need for an open streaming standard
Adobe killed Flash a few years later, leaving a huge vacuum in the industry. Apple was quick to tap on the opportunity with its proprietary HTTP-based adaptive bitrate streaming protocol, HLS (or HTTP Live Streaming).
While HLS addressed every problem associated with Adobe RTMP, it didn’t one. HLS was proprietary just like Adobe’s offering. This development of MPEG had begun.
DASH was the perfect candidate in the post-Flash world. It was an open streaming method not controlled by a corporation. It allowed video playback on browsers supported by open web standards powered by HTML5. MPEG-DASH did not require users to install any plugin and streaming provider deploys a dedicated RSTM server and would run on existing protocols: HTTP and TCP. The firewall wasn’t a problem either for HTTP servers.
The birth of the first open streaming method: MPEG DASH
Apparently, some competitors weren’t fine with the situation Apple was putting them into. One of them was Google. Together, they laid the plan for an alternative to HLS, an industry standard that is not controlled in any way by a single corporate but a consortium of independent stakeholders. More than 50 companies became involved — Microsoft, Netflix, Google, Ericsson, Samsung, and Adobe included — and the effort was coordinated by MPEG with other industry organizations such as 3GPP, DECE, OIPF, and W3C. MPEG published the Dynamic Adaptive Streaming over HTTP (DASH) standard in April 2012 as MPEG-DASH and revised it in 2019 as MPEG-DASH ISO/IEC 23009-1:2019.
How MPEG DASH works?
MPEG DASH expects the video content to be stored on a HTTP server in two parts: Media Presentation Description (MPD) and segments. MPD contains the content’s metadata in various configurations. The segment contains the bitstreams in the form of multiple segments.
MPEG DASH retrieves the MPD as soon a HTTP session is established with the client. MPD provides all the information the DASH client needs to pre-render the video content to be played: media types, available video resolutions, bandwidth range, status of digital rights management (DRM) flag, URI of the video on the HTTP server, etc.
The DASH client parse the information in the MPD file to pick the most appropriate rendition of the video, throws a HTTP GET request to fetch the first set of segments from that rendition, and starts playing the video.
To ensure continuous stream, the client fetches consequent segments according to the available bandwidth and may upscale, downscale segment quality accordingly.
HLS Vs. DASH
The Similarities Between HLS & DASH
In hindsight, MPEG-DASH has expected parallelism to other HTTP-based streaming protocol HLS since they both try to address the modern streaming problems. For instance, they both run over HTTP and employ TCP as their transport protocol.
Streaming videos shouldn’t start over when you change their quality midway. That would be a bad experience for users and unnecessary load on streaming platforms’ servers. To circumvent these problems, both streaming methods slice a video-set into consecutive, independent subsets called segments and encodes each segment at several resolutions (SH, HD, UHD, etc.).
If you’re watching a trailer in full HD and realized it is also available in 4K HDR, you may switch the video quality midway without having to restream the video from scratch. Adaptive streaming means your browser’s inbuilt video player can switch the quality back and forth based on your bandwidth and connection’s quality.
Adjustable segments lengths
Segment lengths on both HLS and MPEG DASH are user adjustable. HLS used to default to 10 seconds until 2016 when Apple switched to 6 seconds default segments. MPEG-DASH allows segments to be anywhere from 2 to 10 seconds although most streaming platforms tend to keep them between 2-4 seconds for interrupted video playbacks.
The differences come into to play
There was one difference to DASH that did not surface until YouTube started streaming content in 4K HDR. HLS restricts HTTP streaming to only two codecs: H.264 and its successor H.265/HEVC. However, that isn’t the case with MPEG DASH. DASH is codec agnostic and will play any codec you throw on it. Not every streaming platform encodes 4K HDR videos in HEVC. MPEG DASH provides the codec freedom they need. Both HLS and DASH has been widely used for react and react native video playback
The Google factor
For example, Google backed its own home-grown codec VP9 (successor to VP8) over HEVC for streaming 4K HDR on YouTube. If you remember, 4K streaming was unavailable on Apple devices until recently. HLS insistence towards HEVC was the reason.
HLS wasn’t compliant with VP9 so Google went for MPEG DASH for streaming 4K HDR and higher quality content on YouTube. As I said, MPEG-DASH is codec-agnostic. That is streaming platforms can transport videos in the codec of their choice.
Majority of video streaming still happens in SD and HD. Video segments in lower quality are encoded in H.264 and are streamed over HLS. HLS has a considerable market share of video streaming market, and it looks like it will remain so for a foreseeable future. MPEG-DASH has a long way to go but it is off to a great start. When it comes to content delivery networks (CDNs), RTMP servers still process a lot of videos for processing.
How Streaming Platform Utilis HLS & DASH?
In our research, we found sufficient evidence to claim that every major streaming platform support DASH in addition to HLS, including Amazon Prime Video, Netflix, Disney Plus and Hulu. Game streaming service Amazon Twitch is an exception as it relies majorly on HLS for live game streaming. Netflix CEO even claimed that MPEG-DASH lowered their network costs.
DASH is the alternative when we need it
As expected by the consortium that led to the formation of MPEG-DASH, Apple eventually did try to steer the development of HLS in favor of its devices. Apple devices support HEVC since 2018. By restricting HLS support to HEVC, Apple abused its industry position to enforce HEVC on device manufacturers, operating platforms, and streaming platform. Had it not for MPEG-DASH as an open alternative, HEVC would had have become the new H.264.
The industry rather than giving into Apple’s pressure switched to MPEG-DASH for 4K HDR content.
HLS Vs DASH, Which One To Pick?
The problem is 1.65 billion Apple devices in use today. We cannot stream a video encoded with MPEG-DASH on an iPhone, iPad, or Apple TV. On macOS the situation is a little tricky, Apple users cannot stream MPEG-DASH on Safari or any application that uses its Webkit engine for web view. However, users Google Chrome and Microsoft Edge on macOS can, but users prefer the default browser.
Moreover, most videos are unavailable in 4K HDR and not everybody has the device and bandwidth capable of handling 4K videos. Many streaming platforms prefer HLS for low quality streaming and only switch to MPEG-DASH for streaming content in 4K on non-Apple devices. Because that is what they have been doing for a long, long time.
It always better to have viable alternatives
Despite being controlled by Apple, HLS pioneered an ingenious method to video streaming employing existing web standards internet protocols. MPEG DASH improved on the method.
Video streaming over HTTP was a huge deal at a time when Flash was getting annoying every day. I don’t remember a time when I could play a Flash video on YouTube without updating Adobe’s plugin.
Whether Apple favored its devices while developing of HLS is still a matter of debate. H.265 was supposed to be the successor to H.264 until it wasn’t. MPEG DASH saved the day and become a mainstream streaming platform and the most viable alternative.
Nevertheless, without these incidents, DASH wouldn’t have grown in popularity and adoption to become a viable alternative to Apple’s proprietary streaming platform. Finally, we have a streaming method that is equally capable and loyalty-free. Competition is good regardless.
With DASH insight the future of video streaming looks better than ever. We expect the growing adoption of MPEG DASH will have a catalytic effect. The demand for 4K HDR content is at an all-time high. I don’t see any reason DASH will gain more streaming market share.
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Head of Digital Marketing at Vdocipher. I love the art of connecting the right product to their users. When i’m not doing that i love getting lost in books.