SSTV (slow-scan television) sends pictures over the radio as sound: each pixel becomes a frequency between 1500 Hz (black) and 2300 Hz (white), line after line. Load a recording: the tool reads the header (VIS code) and rebuilds the picture. Supported mode: Martin M1. Everything happens in your browser.
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In real life: MMSSTV, QSSTV, the Robot36 phone app. The International Space Station sometimes sends SSTV pictures that anyone can receive; in CTFs, a « modem noise » often hides a picture.