#!/usr/bin/env python3 """给已完成的口播 MP4 混入低音量 BGM 和按时间点触发的音效。 用法： python scripts/mix_bgm_sfx.py input.mp4 audio_plan.json --out output/ 计划文件中的音量是线性倍率：1.0=原音量，0.05≈-26dB，0.2≈-14dB。 脚本复制视频流，只重编码音频；不会覆盖输入文件。 """ import argparse import json import math import os import subprocess import sys from pathlib import Path from runtime_support import FFMPEG, FFPROBE def run(cmd): return subprocess.run(cmd, capture_output=True, text=True) def probe(path): r = run([ FFPROBE, "-v", "error", "-show_entries", "format=duration:stream=index,codec_type,codec_name,sample_rate,channels", "-of", "json", str(path), ]) if r.returncode: sys.exit(f"无法读取媒体文件 {path}：\n{r.stderr[-800:]}") data = json.loads(r.stdout) duration = float(data.get("format", {}).get("duration", 0)) return duration, data.get("streams", []) def resolve_media(raw, plan_dir): path = Path(os.path.expandvars(os.path.expanduser(str(raw)))) if not path.is_absolute(): path = (plan_dir / path).resolve() if not path.is_file(): sys.exit(f"音频文件不存在：{path}") duration, streams = probe(path) if not any(s.get("codec_type") == "audio" for s in streams): sys.exit(f"文件没有音频流：{path}") return path, duration def number(value, label, low=None, high=None): try: value = float(value) except (TypeError, ValueError): sys.exit(f"{label} 必须是数字") if not math.isfinite(value): sys.exit(f"{label} 必须是有限数字") if low is not None and value < low: sys.exit(f"{label} 不能小于 {low}") if high is not None and value > high: sys.exit(f"{label} 不能大于 {high}") return value def main(): ap = argparse.ArgumentParser(description="给口播成片加入低音量 BGM 与定点音效") ap.add_argument("video", help="已完成字幕/包装的 MP4") ap.add_argument("plan", help="audio_plan.json") ap.add_argument("--out", required=True, help="输出目录") ap.add_argument("--name", default="preview_字幕包装_音效版.mp4", help="输出文件名") ap.add_argument("--dry-run", action="store_true", help="只验证计划，不渲染") args = ap.parse_args() video = Path(args.video).resolve() plan_path = Path(args.plan).resolve() if not video.is_file(): sys.exit(f"视频不存在：{video}") if not plan_path.is_file(): sys.exit(f"计划不存在：{plan_path}") video_duration, streams = probe(video) if video_duration <= 0 or not any(s.get("codec_type") == "audio" for s in streams): sys.exit("输入视频必须包含有效音轨") with plan_path.open(encoding="utf-8") as f: plan = json.load(f) plan_dir = plan_path.parent voice_volume = number(plan.get("voice_volume", 1.0), "voice_volume", 0, 2) bgm = plan.get("bgm") sfx = plan.get("sfx", []) if not bgm and not sfx: sys.exit("计划中至少需要 bgm 或 sfx") inputs = ["-i", str(video)] filters = [ f"[0:a]aresample=48000,aformat=sample_fmts=fltp:channel_layouts=stereo," f"volume={voice_volume:.6f}[voice]" ] mix_labels = ["[voice]"] summary = [] input_index = 1 if bgm: bgm_path, _ = resolve_media(bgm["file"], plan_dir) volume = number(bgm.get("volume", 0.05), "bgm.volume", 0, 1) fade_in = number(bgm.get("fade_in", 0.8), "bgm.fade_in", 0, video_duration) fade_out = number(bgm.get("fade_out", 1.2), "bgm.fade_out", 0, video_duration) start = number(bgm.get("start", 0), "bgm.start", 0, video_duration) inputs += ["-stream_loop", "-1", "-i", str(bgm_path)] chain = ( f"[{input_index}:a]aresample=48000," f"aformat=sample_fmts=fltp:channel_layouts=stereo," f"atrim=duration={max(0, video_duration-start):.6f},asetpts=PTS-STARTPTS," f"volume={volume:.6f}" ) if fade_in > 0: chain += f",afade=t=in:st=0:d={fade_in:.6f}" if fade_out > 0: fade_start = max(0, video_duration - start - fade_out) chain += f",afade=t=out:st={fade_start:.6f}:d={fade_out:.6f}" if start > 0: chain += f",adelay={round(start*1000)}:all=1" chain += "[bgm]" filters.append(chain) mix_labels.append("[bgm]") summary.append(f"BGM {bgm_path.name} @ {volume:.3f}") input_index += 1 for i, event in enumerate(sfx): sfx_path, sfx_duration = resolve_media(event["file"], plan_dir) at = number(event.get("at"), f"sfx[{i}].at", 0, video_duration) volume = number(event.get("volume", 0.18), f"sfx[{i}].volume", 0, 2) trim = number(event.get("duration", sfx_duration), f"sfx[{i}].duration", 0.01) trim = min(trim, sfx_duration, max(0.01, video_duration - at)) inputs += ["-i", str(sfx_path)] label = f"sfx{i}" filters.append( f"[{input_index}:a]aresample=48000," f"aformat=sample_fmts=fltp:channel_layouts=stereo," f"atrim=duration={trim:.6f},asetpts=PTS-STARTPTS," f"volume={volume:.6f},adelay={round(at*1000)}:all=1[{label}]" ) mix_labels.append(f"[{label}]") summary.append(f"SFX {at:.3f}s {event.get('name', sfx_path.name)} @ {volume:.3f}") input_index += 1 filters.append( "".join(mix_labels) + f"amix=inputs={len(mix_labels)}:duration=first:dropout_transition=0:normalize=0," "alimiter=limit=0.95:attack=5:release=50," f"atrim=duration={video_duration:.6f}[aout]" ) out_dir = Path(args.out).resolve() out_dir.mkdir(parents=True, exist_ok=True) out_path = out_dir / args.name if out_path.resolve() == video: sys.exit("输出文件不能覆盖输入视频") print(f"✓ 计划有效：视频 {video_duration:.3f}s；" + "；".join(summary)) if args.dry_run: return cmd = [ FFMPEG, "-y", "-loglevel", "error", *inputs, "-filter_complex", ";".join(filters), "-map", "0:v:0", "-map", "[aout]", "-c:v", "copy", "-c:a", "aac", "-b:a", "192k", "-movflags", "+faststart", "-shortest", str(out_path), ] r = run(cmd) if r.returncode: sys.exit(f"混音失败：\n{r.stderr[-1600:]}") out_duration, out_streams = probe(out_path) if abs(out_duration - video_duration) > 0.12: sys.exit( f"输出时长异常：输入 {video_duration:.3f}s，输出 {out_duration:.3f}s；" f"文件已保留供排查：{out_path}" ) if not any(s.get("codec_type") == "audio" for s in out_streams): sys.exit(f"输出缺少音轨：{out_path}") print(f"✓ 音效版成片：{out_path}") if __name__ == "__main__": main()