Streaming-artifact analyzer (session QoE + frozen-frame detector)

A small, self-contained Python tool for the artifacts the encoder did NOT cause — the ones a full-reference picture metric (PSNR/SSIM/VMAF) is blind to. It has two modes. (1) SESSION mode: it parses a simple player event log (JSON or CSV: play/stall/resume/switch/end events with timestamps, bitrate, resolution) and computes the delivery QoE numbers a picture score misses — startup time, total stall time, the rebuffering ratio (stall time / (stall + play time)), stall count, mean time between sta