video-assemble

Assemble a final recap video: mux narration audio over the source video, duck the original audio under the narration, render subtitles (SRT/ASS, optionally burned in), and loudness- normalize. Use as the last stage of the video-recap bundle. Consumes the source video + tts_meta.json (+ narration placement); produces recap_<name>.mp4 + subtitles.srt/.ass. 触发词: 视频合成, 混音, 字幕, 压字幕, assemble video, mux, ducking, subtitles, 成片.