In real-time delivery of AV1 over MPEG2-TS using HTTP/3 over QUIC, two fundamental approaches can be identified for improving video quality. The first is bitrate adaptation, represented by Adaptive Bitrate (ABR) , which estimates available bandwidth and selects the optimal resolution and frame rate within that range. The second approach focuses on low-latency control, reducing RTT and ACK delay to increase effective throughput. This study emphasizes the latter perspective and presents the development of a smartphone-oriented application utilizing a QUIC protocol stack capable of estimating and measuring RTT in user space. Through empirical experiments conducted across domestic and international cloud environments, we evaluate how buffer design at distribution servers affects video quality. This paper shares experimental methods, observations, and guidelines for designing real-time streaming systems using HTTP/3 over QUIC.