SYNTHETIC TEACHING VIDEO — 4 seconds; no speech.
0–2s: a white square is on the left of a dark field. A steady tone sounds.
2–4s: the square is on the right. The steady tone continues.
No client footage, service outcome or accessibility certification.

合成教学视频，4秒，无对白。
0—2秒：深色画面左侧有白色方块，持续稳定音调。
2—4秒：方块移到右侧，音调持续。
不含客户影像、服务成果或可访问性认证。