Around 60% of Internet traffic in the US consists of the streaming of high-quality video. The popularity of this over the top (OTT) content, using the HTTP system, has led to the standardisation of MPEG Dynamic Adaptive Streaming over HTTP (DASH). The MPEG-DASH standard, as this is known, means that video can be streamed smoothly and seamlessly.
We are going to take a look at the Quality of Experience (QoE) of DASH based services. This involves looking at what QoE means and how it can be measured. We are also going to look at what areas of a DASH based service are considered when deciding on the overall QoE.
What is Quality of experience?
Quality of Experience (QoE) has evolved from the term Quality of Service (QoS). The QoS was taken to mean the overall aspects of a telecommunications service that lead to the service being able to meet the needs of its users. The QoE is slightly different in that this is defined as the way the end user of telecommunications perceives the service they receive. This standard concerns the level of satisfaction the user feels and to what level their expectations are met.
QoE for the DASH based system
We have given you an overall view of what QoE is about, but what does it mean for the DASH based experience?
In order to create an application specific QoE definition you need to take into account the requirements of the specific domain and relate them to the general definition of QoE. The main influence factors to be considered, as far as DASH based adaptive streaming services are concerned are:
- Timing of the initial start-up.
- Buffering or stalling.
- Impact of quality switches.
- Media throughput measured in media bits per second.
Let’s take a look at these aspects in more detail.
Timing of the initial start-up
The start-up time is the total time between the user accessing the video stream and start of the playback. Generally, this time should be short but it’s worth noting that the time can be slightly longer in the case of the streaming of live events and short clips than when full length on demand videos are being watched.
Buffering or stalling
Stalling happens as the result of buffer underruns and accounts for many reports of low QoE from users. Stalling should be avoided if at all possible even if this is done by extending the initial start-up time.
Impact of quality switches
Quality switches occur when the network quality conditions are switched to try and avoid buffer underruns. They can cause low QoE if they happen all the time or the switch is from a very high-quality standard to an extremely low-quality standard.
Media throughput measured in media bits per second
This is the rate of throughput and in general the higher the rate the better the QoE. That being said, it’s important to remember that this should never be used as a measure on its own, without taking all of the other aspects into consideration.
These are the major aspects that help to determine QoE in relation to the MPEG-DASH standard. Of course there are also other aspects that could influence the way a user views their experience, such as the availability of multiple languages or subtitles. QoE should always be considered in relation to the service itself.