ffmpeg - 降低视频中对话的背景音乐音量

Question

我有一个视频，里面有一些背景音乐。

我希望在视频中的特定位置添加一段口头对话，以便在对话音频的整个持续时间内降低背景音乐。

我使用 sidechaincompress 找到了类似的解决方案，它仅适用于 mp3。我对其进行了一些更改，以便它也包含视频 (-map 0:v)。然而，现在对话一结束，音频就会被缩短。

ffmpeg -i video-with-bg-music.mp4 -i dialogue.mp3 -c:v libx264 -filter_complex "[1:a]asplit=2[sc][mix];[0:a][sc]sidechaincompress=threshold=0.003:ratio=20[bg];[bg][mix]amerge[final]" -map 0:v -map [final] final.mp4

我不是使用 ffmpeg 的专业人士，可能不知道 filter_complex 发生了什么。请帮帮我。

编辑：

@kesh 建议的解决方案的输出日志

ffmpeg -i video_bg.mp4 -i dialogues.mp3 -filter_complex "[1:a]adelay=0,apad,asplit=2[sc][mix];[0:a][sc]sidechaincompress=threshold=0.003:ratio=20[bg];[bg][mix]amix=duration=shortest[out]" -map 0:v -map [out] video_bg_speech.mp4
ffmpeg version 4.2.4-1ubuntu0.1 Copyright (c) 2000-2020 the FFmpeg developers
  built with gcc 9 (Ubuntu 9.3.0-10ubuntu2)
  configuration: --prefix=/usr --extra-version=1ubuntu0.1 --toolchain=hardened --libdir=/usr/lib/x86_64-linux-gnu --incdir=/usr/include/x86_64-linux-gnu --arch=amd64 --enable-gpl --disable-stripping --enable-avresample --disable-filter=resample --enable-avisynth --enable-gnutls --enable-ladspa --enable-libaom --enable-libass --enable-libbluray --enable-libbs2b --enable-libcaca --enable-libcdio --enable-libcodec2 --enable-libflite --enable-libfontconfig --enable-libfreetype --enable-libfribidi --enable-libgme --enable-libgsm --enable-libjack --enable-libmp3lame --enable-libmysofa --enable-libopenjpeg --enable-libopenmpt --enable-libopus --enable-libpulse --enable-librsvg --enable-librubberband --enable-libshine --enable-libsnappy --enable-libsoxr --enable-libspeex --enable-libssh --enable-libtheora --enable-libtwolame --enable-libvidstab --enable-libvorbis --enable-libvpx --enable-libwavpack --enable-libwebp --enable-libx265 --enable-libxml2 --enable-libxvid --enable-libzmq --enable-libzvbi --enable-lv2 --enable-omx --enable-openal --enable-opencl --enable-opengl --enable-sdl2 --enable-libdc1394 --enable-libdrm --enable-libiec61883 --enable-nvenc --enable-chromaprint --enable-frei0r --enable-libx264 --enable-shared
  libavutil      56. 31.100 / 56. 31.100
  libavcodec     58. 54.100 / 58. 54.100
  libavformat    58. 29.100 / 58. 29.100
  libavdevice    58.  8.100 / 58.  8.100
  libavfilter     7. 57.100 /  7. 57.100
  libavresample   4.  0.  0 /  4.  0.  0
  libswscale      5.  5.100 /  5.  5.100
  libswresample   3.  5.100 /  3.  5.100
  libpostproc    55.  5.100 / 55.  5.100
Input #0, mov,mp4,m4a,3gp,3g2,mj2, from 'video_bg.mp4':
  Metadata:
    major_brand     : isom
    minor_version   : 512
    compatible_brands: isomiso2avc1mp41
    encoder         : Lavf58.29.100
  Duration: 00:01:50.12, start: 0.000000, bitrate: 157 kb/s
    Stream #0:0(und): Video: h264 (High) (avc1 / 0x31637661), yuv420p, 720x1280 [SAR 1:1 DAR 9:16], 146 kb/s, 24 fps, 24 tbr, 12288 tbn, 48 tbc (default)
    Metadata:
      handler_name    : VideoHandler
    Stream #0:1(und): Audio: aac (LC) (mp4a / 0x6134706D), 44100 Hz, stereo, fltp, 128 kb/s (default)
    Metadata:
      handler_name    : SoundHandler
[mp3 @ 0x5577fa3b6740] Estimating duration from bitrate, this may be inaccurate
Input #1, mp3, from 'dialogue.mp3':
  Duration: 00:00:17.33, start: 0.000000, bitrate: 32 kb/s
    Stream #1:0: Audio: mp3, 24000 Hz, mono, fltp, 32 kb/s
File 'video_bg_speech.mp4' already exists. Overwrite ? [y/N] y
Stream mapping:
  Stream #0:1 (aac) -> sidechaincompress:main (graph 0)
  Stream #1:0 (mp3float) -> adelay (graph 0)
  Stream #0:0 -> #0:0 (h264 (native) -> h264 (libx264))
  amix (graph 0) -> Stream #0:1 (aac)
Press [q] to stop, [?] for help
[libx264 @ 0x5577fa446040] using SAR=1/1
[libx264 @ 0x5577fa446040] using cpu capabilities: MMX2 SSE2Fast SSSE3 SSE4.2 AVX FMA3 BMI2 AVX2
[libx264 @ 0x5577fa446040] profile High, level 3.1
[libx264 @ 0x5577fa446040] 264 - core 155 r2917 0a84d98 - H.264/MPEG-4 AVC codec - Copyleft 2003-2018 - http://www.videolan.org/x264.html - options: cabac=1 ref=3 deblock=1:0:0 analyse=0x3:0x113 me=hex subme=7 psy=1 psy_rd=1.00:0.00 mixed_ref=1 me_range=16 chroma_me=1 trellis=1 8x8dct=1 cqm=0 deadzone=21,11 fast_pskip=1 chroma_qp_offset=-2 threads=18 lookahead_threads=3 sliced_threads=0 nr=0 decimate=1 interlaced=0 bluray_compat=0 constrained_intra=0 bframes=3 b_pyramid=2 b_adapt=1 b_bias=0 direct=1 weightb=1 open_gop=0 weightp=2 keyint=250 keyint_min=24 scenecut=40 intra_refresh=0 rc_lookahead=40 rc=crf mbtree=1 crf=23.0 qcomp=0.60 qpmin=0 qpmax=69 qpstep=4 ip_ratio=1.40 aq=1:1.00
[Parsed_sidechaincompress_3 @ 0x5577faed3f00] No channel layout for input 1
Output #0, mp4, to 'video_bg_speech.mp4':
  Metadata:
    major_brand     : isom
    minor_version   : 512
    compatible_brands: isomiso2avc1mp41
    encoder         : Lavf58.29.100
    Stream #0:0(und): Video: h264 (libx264) (avc1 / 0x31637661), yuv420p(progressive), 720x1280 [SAR 1:1 DAR 9:16], q=-1--1, 24 fps, 12288 tbn, 24 tbc (default)
    Metadata:
      handler_name    : VideoHandler
      encoder         : Lavc58.54.100 libx264
    Side data:
      cpb: bitrate max/min/avg: 0/0/0 buffer size: 0 vbv_delay: -1
    Stream #0:1: Audio: aac (LC) (mp4a / 0x6134706D), 24000 Hz, mono, fltp, 69 kb/s (default)
    Metadata:
      encoder         : Lavc58.54.100 aac
frame=  480 fps=325 q=-1.0 Lsize=     517kB time=00:00:19.87 bitrate= 213.0kbits/s speed=13.5x    
video:353kB audio:152kB subtitle:0kB other streams:0kB global headers:0kB muxing overhead: 2.388190%
[libx264 @ 0x5577fa446040] frame I:2     Avg QP:15.99  size:136135
[libx264 @ 0x5577fa446040] frame P:121   Avg QP:16.86  size:   603
[libx264 @ 0x5577fa446040] frame B:357   Avg QP:26.34  size:    43
[libx264 @ 0x5577fa446040] consecutive B-frames:  0.6%  0.4%  0.6% 98.3%
[libx264 @ 0x5577fa446040] mb I  I16..4:  2.3% 65.7% 32.1%
[libx264 @ 0x5577fa446040] mb P  I16..4:  0.0%  0.1%  0.1%  P16..4:  1.1%  0.1%  0.1%  0.0%  0.0%    skip:98.5%
[libx264 @ 0x5577fa446040] mb B  I16..4:  0.0%  0.0%  0.0%  B16..8:  0.2%  0.0%  0.0%  direct: 0.0%  skip:99.8%  L0:55.5% L1:44.5% BI: 0.0%
[libx264 @ 0x5577fa446040] 8x8 transform intra:62.5% inter:56.6%
[libx264 @ 0x5577fa446040] coded y,uvDC,uvAC intra: 89.6% 89.0% 78.7% inter: 0.0% 0.1% 0.0%
[libx264 @ 0x5577fa446040] i16 v,h,dc,p: 37%  5%  8% 50%
[libx264 @ 0x5577fa446040] i8 v,h,dc,ddl,ddr,vr,hd,vl,hu: 24% 16%  6%  6%  9%  9%  9% 10%  9%
[libx264 @ 0x5577fa446040] i4 v,h,dc,ddl,ddr,vr,hd,vl,hu: 25% 18%  7%  6% 11%  9%  9%  7%  7%
[libx264 @ 0x5577fa446040] i8c dc,h,v,p: 42% 22% 20% 15%
[libx264 @ 0x5577fa446040] Weighted P-Frames: Y:0.0% UV:0.0%
[libx264 @ 0x5577fa446040] ref P L0: 46.3%  2.9% 19.3% 31.5%
[libx264 @ 0x5577fa446040] ref B L0: 45.6% 54.0%  0.4%
[libx264 @ 0x5577fa446040] ref B L1: 97.0%  3.0%
[libx264 @ 0x5577fa446040] kb/s:144.26
[aac @ 0x5577fa3b9940] Qavg: 307.060

Answer 1

试试这个（在 3 秒标记处插入的短片）：

[1:a]aresample=44100,adelay=3000,apad,asplit=2[sc][mix];\
[0:a][sc]sidechaincompress=threshold=0.003:ratio=20[bg];\
[bg][mix]amix=duration=shortest[out]

• aresample 使对话框的采样率与视频的采样率相匹配。
• adelay 将剪辑放置在正确的位置（注意延迟以毫秒为单位）
• apad 以静音无限期地延长短流
• amix 组合了 2 个流，并且视频音频结束时停止

附录：

如果mp4没有音频，请尝试：

ffmpeg -i video-with-bg-music.mp4 -i dialogue.mp3 \
  -af [1:a]adelay=3000,apad \
  -shortest final.mp4

音频过滤器图中的apad扩展音频流，以及-shortest输出选项将其切断视频流结束。

调试示例

ffmpeg -filter_complex \
    [1:a]aresample=44100,apad,asplit=2[sc][mix];\
    [0:a][sc]sidechaincompress=threshold=0.003:ratio=20[bg];\
    [bg][mix]amix=duration=shortest[out] \
  -f lavfi -i anoisesrc=d=60:c=pink:r=44100:a=0.5 \
  -f lavfi -i sine=220:4:d=5 \
  -map [out] output.mp3