Low encoding overhead ultra-low latency streaming via HESP through sparse initialization streams

HESP, the High Efficiency Streaming Protocol [4], realizes ultra-low latencies and ultra-short start-up times by combining two feeds, the keyframe-only Initialization Stream and the ultra-low latency CMAF-CTE Continuation Stream. HESP uses a keyframe from the Initialization Stream to start playback (via keyframe injection) of the Continuation Stream extremely close to the live edge. In previous research [5], the impact of the HESP keyframe injection on the video quality has been proven to be very low or even negligible. In contrast to the trivial double encoding for each quality in the bitrate ladder, in this paper we show that the overhead of the generation of the keyframe-only Initialization Streams can be reduced. We designed an approach in which the frequency of keyframes in the Initialization Streams is defined by a trade-off between the encoding overhead and two metrics in the viewing QoE: start-up time and time that it takes to switch to the highest feasible video quality of the ABR ladder. More specifically, for each quality Qi, fi is defined such that (i) switching to Qi, either for start-up or for switching to Qi as a higher quality, takes [EQUATION] additional delay, and (ii) there always is a Qi, lower than Qcurrent (unless Qcurrent is the lowest quality) to which the player can switch down instantly, which is needed in case of network problems. The resulting impact on the viewer QoE is characterizedby occasional (whenever an ABR switch to a higher quality is needed) short intervals [EQUATION] during which playback potentially is done at a lower than feasible video quality. Based on measurements, the proposed approach results in an overhead when encoding Initialization Streams of only 15 to 20%. Compared to "standard" HESP, the viewer QoE reduction is hardly noticeable.