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The video access time is defined by two factors, preparation time and pre-playout (also called initial) buffering, which depends on the CDN streaming performance and OTT application configuration, for example client/buffer settings. The video presentation quality is defined by resolution value, resolution switches, frame rate and playback interruptions (rebufferings) during playback and by the video playout duration (e.g., streaming session cut-off). Factors impacting the quality are determined both by the configuration/ construction of the OTT video service (e.g. client/ buffer settings and schemes, codec configurations) and by the network performance (e.g. bandwidth/ throughput, delay, jitter, loss).
Last, but not least, the original content quality and dynamicity are factors impacting the video playback quality. High resolution, high quality and dynamic video content can be more sensitive to network performance degradation and thus to user experience, than lower resolution, lower quality and less dynamic (or stationary) video content.
Table 1 presents a map between the user experience video quality dimensions, their impacting factors, and their source.
USER’S PERCEIVED VIDEO STREAMING QUALITY
IMPACTING FACTORS
SOURCE OF DEGRADATION ****
Resolution
Network instantaneous behavior (real time)
bandwidth/throughput
Frame rate
Network* long term behavior (video session level)
Rebuffering**
Delay*, jitter, loss
Perceived video quality (video presentation/playback)
Video content
CDN/Service provider
Video codec
OTT application
Video client settings (pre-filling/initial buffering)
OTT application
Network behavior
Perceived waiting time
Video preparation time
CDN/OTT application
Video start failure***
CDN/OTT application
Perceived retainability
Video streaming cut off
RF, IP congestion
Network
* It should be noted that delay is rooted not only in the network (generally between 5ms-2min), but also in the encoding (50ms-10sec) and decoding (15ms-2sec) processes; thus, in the OTT application itself. Due to the small values when compared with the network delay, the delay from the OTT application is not considered in the discussion.
** Close to half (44%) of viewers say it’s the most frustrating aspect of the streaming experience.
*** An important factor since users are more likely to abandon viewing due to it.
**** Based on the consideration that the original content has the best quality
Table 1. Comparison between generic OTT telephony and WhatsApp MOS in LTE across varying radio conditions
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