Video Quality Adaptation for Limiting Transcoding Energy Consumption in Video Servers

Dynamic adaptive streaming over HTTP (DASH) inherently requires many transcoding operations to produce various bit-rate versions. However, transcoding is highly computationally intensive, resulting in significant power consumption in transcoding servers. To limit the amount of energy consumption in transcoding servers, some transcoding tasks can be skipped and executed later, but this poses several questions, such as (1) which versions can be transcoded before an actual streaming session, (2) how to limit total amount of transcoding energy consumption, and (3) how to handle requests to the untranscoded versions. To address this, we first introduce the concept of transcoding gain to express the overall video quality assigned to each transcoded version by considering segment popularity and go on to propose an algorithm that determines when and which versions should be transcoded with the aim of maximizing the overall transcoding gain by limiting energy consumption. To achieve this, it allows lower bit-rate versions to be streamed than are requested, at the cost of minimal video quality degradation by considering the overall video quality. The proposed scheme was implemented on a clustered system where various issues were resolved. The experimental results show that the transcoding selection algorithms can effectively control the amount of power consumption, minimizing the effect of overall video quality degradation. For example, it can save up to 65% energy when video quality degradation is allowed to be 4.3% at maximum compared with the scheme that transcodes all the versions.