Mixed-Resolution HESP for More Efficient Fast Channel Switching and Packet-Loss Repair

Low-delay live streaming applications desire fast channel switching and packet-loss repair capabilities. However, existing methods that provide these capabilities have a negative impact on the stream of steady-state users. To minimize this impact, techniques such as the High Efficiency Streaming Protocol (HESP) utilize keyframe injection. Such techniques combine compression-efficient normal streams with corresponding companion streams that are used in case of random access or packet loss. Unfortunately, because a companion stream is needed for every normal stream, the distribution cost and encoding complexity are considerable costs. Additionally, injecting a companion keyframe into a normal stream causes a bitrate spike. Therefore, this paper evaluates the impact of utilizing mixed-resolution keyframe injection in the H.266/VVC standard. By providing a single companion stream for all normal streams of a bitrate ladder, the three mentioned downsides can be mitigated. We found that injecting a lower-resolution keyframe effectively reduces the bitrate spike, at the cost of only a modest quality loss. For dynamic video content, the quality impact reduces over time, and is less perceptible than traditional packet-loss repair using frame copy. In conclusion, mixed-resolution HESP can reduce the bitrate spike and computational/distribution overhead of HESP when enabling fast channel switching or packet-loss repair.