Prove SRT survives packet loss and RTMP doesn't: MediaMTX, ffmpeg, and tc netem on one laptop

TL;DR We'll run MediaMTX locally, publish a test pattern to it over RTMP and over SRT, pull both back out, then add packet loss to the network path with tc netem. RTMP stalls and reconnects; SRT retransmits inside its latency window and keeps going. Then we'll size that window properly from a real RTT and push it to a relay. RTMP rides on TCP, so one lost packet blocks everything behind it until it's retransmitted. SRT rides on UDP with its own selective retransmission and a latency budget you choose.