With this post, I’ll be wrapping up a multi-part discussion about measuring video quality. In the first part, I described Mean Opinion Scores and how these scores provide a quantitative value of multimedia quality. Last time, I spoke about “full-reference” and “reference-free” measurement techniques, and gave some advantages of each.
Today, we discuss ways that mobile video quality problems may be introduced, some of the more common types of quality issues, and some of the causes behind these.
Most video quality problems may be introduced at several points along the video distribution chain:
During video creation. While most professionally-produced video content is created by trained technicians using expensive devices, most user-generated video content is recorded with poor-quality cameras. In addition, the person doing the recording will often have shaky hands. This leads to quality problems that are introduced as soon as the video is created.
During transcoding. While today’s algorithms for encoding and decoding video content are quite sophisticated and very good at preserving quality, the nature of compression causes some loss of quality each time content goes through a coding cycle. Therefore, the number of encodes and decodes should be kept to a minimum. However, in the real world, content must often be translated (or “transcoded”) between algorithms. This can be because different devices support different algorithms, or because one algorithm might be great for display quality while another is better for transport efficiency. In today’s telecommunications networks, it is common for video content to be transcoded several times between creation and delivery; each of these transcodes can contribute to reducing video quality.
During video transmission. IP networks suffer from impairments such as packet loss and jitter. While these problems have affected voice services for years, the human ear can recover from communication gaps better than the human eye. Even a small glitch in a video communications stream can cause distraction for a viewer.
When displaying video on a device. Even the best video content can be unsatisfying if it is displayed on a poor viewing device. Most of today’s mobile devices were designed to provide a high-quality voice experience, while video capabilities may be limited. Higher-quality video displays require a lot of power, so device makers may consider tradeoffs like offering extended battery life by sacrificing display quality in a mobile device.
While the previous paragraphs discussed how quality problems may be introduced during the process of video creation and distribution, the next will describe several of the more common types of problems that may be experienced (and some of the potential causes of each):
I hope that these last few posts have been helpful as a reference to any of our customers (or potential customers) that are considering tools and systems for measuring video quality. The increasing focus on video quality, and particularly the quality of mobile video, is an important step forward for our industry. At Dialogic, we welcome this increased attention to quality, as our business is focused on providing our customers with the highest-quality, highest-performance video solutions. Please stay tuned to this space in the next few months, and you’ll be hearing more about our efforts related to video quality measurement and improvement.
In the meantime, if you would like to learn more about this topic, we have a white paper available for free download here. And please take a moment to let us know what you are thinking about this subject – I’d enjoy the opportunity to continue the discussion!