MPEG-Dash protocol
Did you use YouTube, Netflix or HBO more during the pandemic? Not only you! However, since you spend a significant amount of time watching video on the web, learn about MPEG-DASH – one of the most popular video transfer protocols.
What is MPEG-DASH and who uses it?
The MPEG-DASH protocol is an adaptive protocol based on HTTP technology. It is used for multimedia streaming over the Internet and widely used by VOD platforms. The MPEG-DASH protocol is also used in live video broadcasting.
MPEG-DASH is used, among others, by: Netflix, YouTube, HBO, Vimeo or other websites that enable watching videos on the Internet.
Jak to się zaczęło? MPEG (Moving Pictures Expert Group) opracował technologię MPEG-DASH jako alternatywę (i konkurencję) dla protokołu HLS (Apple HTTP Live Streaming).
The streaming process using MPEG-DASH is carried out in 3 steps:
- Coding and segmentation: video segmentation, index file creation and encoding.
- Providing encoded video to the user.
- Decoding and playback: the player automatically adjusts the video quality to the network conditions.
MPEG-DASH works similar to HLS. It divides the video into smaller fragments and encodes them, enabling later decoding and playback of the material at various quality levels depending mainly on network parameters. As a result, video can be streamed and consumed regardless of the end device or the signal bit rate. At the same time, the user can freely change the quality of the viewed material depending on his own preferences.
We’ll write more about the similarities and differences between MPEG-DASH and HLS later in this article.
How does Adaptive Bitrate Streaming work?
You’ve probably noticed many times when watching a particular video when the image suddenly changed from pixelated to sharp (or vice versa). This is exactly what Adaptive Streaming (ABR) is.
ABR is nothing more than a multimedia streaming method that allows dynamic (adaptive) adjustment of video quality (bitrate) to network bandwidth, allowing the recipient to switch between different qualities of encoded video.
ABR technology is used to download video from one source and transcode the source material into several different quality versions. These versions differ in size, so they can be adapted to be played without a buffer on various devices and with transmission using Internet connections of different speeds.
As a result, viewers watching a video on a TV screen and having a fast Internet connection can consume content with high frames per second and in high definition. On the other hand, smartphone users with poor connectivity can watch the same movie in much lower quality.
The video is delivered to the recipient not in the form of a continuous stream, but as a series of material cut into segments up to 10 seconds long. This allows ABR technology to automatically adjust to the bit rate and resolution options selected by the viewer. When the link speed drops, the ABR also reduces the quality of the material. When the speed of the internet connection speeds up or when the viewer sets a higher resolution, ABR will provide better video quality.
By using adaptive streaming technology, the MPEG-DASH protocol ensures relatively stable video quality. However, this is paid for by the initial delay resulting from the need to download individual video segments.
Differences between HLS and DASH
Technically, HLS and DASH are similar technologies. The main difference is the ownership of the protocol and how its licenses are distributed. The HLS protocol is owned and used by Apple. In turn, the DASH protocol is based on an open source license.
Thus, the HLS protocol is used by Apple, but on Apple devices you can also receive signals transmitted in the DASH protocol.
While the HLS standard clearly specifies the use of specific video (H.264 and H.265) and audio codecs, the DASH protocol works independently of the selected codecs. Therefore, the quality of the material transmitted via the DASH protocol depends on the codecs used.
The container format is also worth mentioning. The DASH protocol uses the MP4 format, with HLS using the MPEG-2 or MPEG-TS format. Moreover, the video fragments in HLS are segmented into 2-4 seconds long segments, while MPEG-DASH creates 6-10 seconds long segments.
Delays
The delays in both MPEG-DASH and HLS are not small and amount to about 4-5 seconds. The delay depends on the streaming speed. Now, to reduce latency, DASH has started using CMAF technology, and HLS has modified its protocol to implement the low-latency HLS extension.
Support for MPEG-Dash in Storm
Storm Streaming server supports both the classic MPEG-DASH protocol as well as HLS, LL-HLS and CMAF, thanks to which, depending on the needs and technological choices, it is able to cope with any video-streaming project. We also invite you to familiarize yourself with our proprietary Storm protocol, which offers a definite qualitative leap reducing delays to 1 second.