Quality of Experience (QoE) is the whole end-to-end quality a viewer actually perceives when watching, not just how each frame looks but the entire experience: the picture quality plus startup delay, rebuffering stalls, and bitrate switching. It is the measure that matters because it is what makes a viewer stay or abandon a stream. The catch is that QoE losses live mostly in delivery and are invisible to a full-reference picture metric like PSNR or VMAF: a frozen frame has perfect picture quality and a terrible experience. ITU-T P.1203 recognizes this directly by combining lossy compression, spatial or temporal downscaling, and stalling, including initial loading delay, into one Mean Opinion Score for a streaming session. QoE is measured with dedicated streaming metrics such as rebuffering ratio, startup time, and switching rate, and it stands apart from QoS, which describes only what the network delivered.
