What affects the quality of adaptive video streams?

• Quality Switches
• Amplitude
• Frequency
• Stallings
• Duration 
• Frequency
• Initial Startup Delay

There are some surveys on the quality of experience for adaptive video streaming:

• Quality of Experience and HTTP adaptive streaming: A review of subjective studies [1]
• A Survey on Quality of Experience of HTTP Adaptive Streaming [2]
• User experience modeling for DASH video [3]

QoE is affected by spatial and temporal quality of the video stream. Initial delay, total stall duration, and number of stalls affect the temporal quality. Average video quality, number of switches, and average switch magnitude affect the spatial quality. In [3], the effect of each of these factors has been quantified.

Some important notes:

• Gradual multiple variations are preferred over abrupt variations.
• Constant quality is usually preferred to varying quality.
• In general, providing a bitrate as high as possible does not necessarily lead to the highest QoE.
• All is end that ends well: the end quality of the video has a definite impact on the perceived quality.
• The effect of spatial and temporal switching varies depending on the content type. 
• A single long stalling is preferred over multiple short freezes.
• Regular freezes are preferred over irregular freezes.
• Tolerable startup delay is dependent on the type of the application.
• Users prefer to wait longer if they can get less video stalling.       

Metrics

• Number of Quality Changes (NoC) [5]
• Number of Interruptions (NoI) [5]
• Percentage of Interruptions(PoI) [5]
• Impairment due to initial delay [3]
• Impairment due to stall [3]
• Impairment due to level fluctuations [3]
• Impairment due to low level video quality [3]
• Average playback Quality (APQ) [4]
• Playback Smoothness (PS) [6]
• Interruption Ratio [4]

References

[1] Garcia, M-N., et al. "Quality of experience and HTTP adaptive streaming: A review of subjective studies." Quality of Multimedia Experience (QoMEX), 2014 Sixth International Workshop on. IEEE, 2014.

[2] Seufert, Michael, et al. "A survey on quality of experience of http adaptive streaming." IEEE Communications Surveys & Tutorials 17.1 (2015): 469-492.
[3] Liu, Yao, et al. "User experience modeling for DASH video." 2013 20th International Packet Video Workshop. IEEE, 2013.
[4] S. Xiang, L. Cai, and J. Pan, “Adaptive scalable video streaming in wireless networks,” in Proc. of ACM MMSys, Feb. 2012, pp. 167–172.
[5] Yan, Zhisheng, Jingteng Xue, and Chang Wen Chen. "QoE continuum driven HTTP adaptive streaming over multi-client wireless networks." 2014 IEEE International Conference on Multimedia and Expo (ICME). IEEE, 2014.
[6] S. Nelakuditi, R. Harinath, E. Kusmierek, and Z. Zhang. Providing smoother quality layered video stream. In ACM NOSSDAV’00, June 2000.