video - 使用 -ffmpeg- 将音频混合并叠加到 4x4 视频中

Question

感谢@llogan 回复我的帖子here ，我已经能够将 16 个不同的视频合并成一个 4x4 .mp4 电影。
不幸的是，我还希望添加 音频从这 16 个剪辑中提取并覆盖它们。使用原样的代码，它会从调用中声明的第一个剪辑中获取音频。
我试过了:

ffmpeg -i a.mp4 -i b.mp4 -i c.mp4 -i d.mp4 -i e.mp4 -i f.mp4 -i g.mp4 -i h.mp4 -i i.mp4 -i j.mp4 -i k.mp4 -i l.mp4 -i m.mp4 -i n.mp4 -i o.mp4 -i q.mp4 -i p.mp4 \
 -filter_complex \
 "[0:v]scale=iw/4:-1[v0];[1:v]scale=iw/4:-1[v1];[2:v]scale=iw/4:-1[v2]; \ 
  [3:v]scale=iw/4:-1[v3];[4:v]scale=iw/4:-1[v4];[5:v]scale=iw/4:-1[v5]; \
  [6:v]scale=iw/4:-1[v6];[7:v]scale=iw/4:-1[v7];[8:v]scale=iw/4:-1[v8]; \ 
  [9:v]scale=iw/4:-1[v9];[10:v]scale=iw/4:-1[v10];[11:v]scale=iw/4:-1[v11]; \
  [12:v]scale=iw/4:-1[v12];[13:v]scale=iw/4:-1[v13];[14:v]scale=iw/4:-1[v14]; \ 
  [15:v]scale=iw/4:-1[v15]; \
  [v0][v1][v2][v3][v4][v5][v6][v7][v8][v9][v10][v11][v12][v13][v14]  
[v15]xstack=inputs=16:layout=0_0|w0_0|w0+w1_0|w0+w1+w2_0|0_h0|w4_h0|w4+w5_h0|w4+w5+w6_h0|0_h0+h4|w8_h0+h4|w8+w9_h0+h4|w8+w9+w10_h0+h4|0_h0+h4+h8|w12_h0+h4+h8|w12+w13_h0+h4+h8|w12+w13+w14_h0+h4+h8; \
  [0:a][1:a][2:a][3:a][4:a][5:a][6:a][7:a][8:a][9:a][10:a][11:a][12:a][13:a][14:a][15:a]amerge=inputs=16[a]" \
  -map "[a]" -ac 2 \
output.mp4

同时合并倒数第三行作为合并音频输入的尝试，但它会产生:

ffmpeg version 4.3.2-0+deb11u1ubuntu1 Copyright (c) 2000-2021 the FFmpeg developers
  built with gcc 10 (Ubuntu 10.2.1-20ubuntu1)
  configuration: --prefix=/usr --extra-version=0+deb11u1ubuntu1 --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-gnutls --enable-ladspa --enable-libaom --enable-libass --enable-libbluray --enable-libbs2b --enable-libcaca --enable-libcdio --enable-libcodec2 --enable-libdav1d --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-librabbitmq --enable-librsvg --enable-librubberband --enable-libshine --enable-libsnappy --enable-libsoxr --enable-libspeex --enable-libsrt --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-pocketsphinx --enable-libmfx --enable-libdc1394 --enable-libdrm --enable-libiec61883 --enable-nvenc --enable-chromaprint --enable-frei0r --enable-libx264 --enable-shared
  WARNING: library configuration mismatch
  avcodec     configuration: --prefix=/usr --extra-version=0+deb11u1ubuntu1 --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-gnutls --enable-ladspa --enable-libaom --enable-libass --enable-libbluray --enable-libbs2b --enable-libcaca --enable-libcdio --enable-libcodec2 --enable-libdav1d --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-librabbitmq --enable-librsvg --enable-librubberband --enable-libshine --enable-libsnappy --enable-libsoxr --enable-libspeex --enable-libsrt --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-pocketsphinx --enable-libmfx --enable-libdc1394 --enable-libdrm --enable-libiec61883 --enable-nvenc --enable-chromaprint --enable-frei0r --enable-libx264 --enable-shared --enable-version3 --disable-doc --disable-programs --enable-libaribb24 --enable-liblensfun --enable-libopencore_amrnb --enable-libopencore_amrwb --enable-libtesseract --enable-libvo_amrwbenc
  libavutil      56. 51.100 / 56. 51.100
  libavcodec     58. 91.100 / 58. 91.100
  libavformat    58. 45.100 / 58. 45.100
  libavdevice    58. 10.100 / 58. 10.100
  libavfilter     7. 85.100 /  7. 85.100
  libavresample   4.  0.  0 /  4.  0.  0
  libswscale      5.  7.100 /  5.  7.100
  libswresample   3.  7.100 /  3.  7.100
  libpostproc    55.  7.100 / 55.  7.100
Input #0, mov,mp4,m4a,3gp,3g2,mj2, from 'ang.mp4':
  Metadata:
    major_brand     : isom
    minor_version   : 512
    compatible_brands: isomiso2avc1mp41
    encoder         : Lavf58.45.100
  Duration: 00:00:10.00, start: 0.000000, bitrate: 480 kb/s
    Stream #0:0(und): Video: h264 (High) (avc1 / 0x31637661), yuv420p, 640x360, 271 kb/s, 60 fps, 60 tbr, 15360 tbn, 120 tbc (default)
    Metadata:
      handler_name    : VideoHandler
    Stream #0:1(und): Audio: aac (LC) (mp4a / 0x6134706D), 48000 Hz, stereo, fltp, 194 kb/s (default)
    Metadata:
      handler_name    : SoundHandler
Input #1, mov,mp4,m4a,3gp,3g2,mj2, from 'atv.mp4':
  Metadata:
    major_brand     : isom
    minor_version   : 512
    compatible_brands: isomiso2avc1mp41
    encoder         : Lavf58.45.100
  Duration: 00:00:17.00, start: 0.000000, bitrate: 259 kb/s
    Stream #1:0(und): Video: h264 (High) (avc1 / 0x31637661), yuv420p, 640x360, 53 kb/s, 60 fps, 60 tbr, 15360 tbn, 120 tbc (default)
    Metadata:
      handler_name    : VideoHandler
    Stream #1:1(und): Audio: aac (LC) (mp4a / 0x6134706D), 48000 Hz, stereo, fltp, 193 kb/s (default)
    Metadata:
      handler_name    : SoundHandler
Input #2, mov,mp4,m4a,3gp,3g2,mj2, from 'bor.mp4':
  Metadata:
    major_brand     : isom
    minor_version   : 512
    compatible_brands: isomiso2avc1mp41
    encoder         : Lavf58.45.100
  Duration: 00:00:09.00, start: 0.000000, bitrate: 255 kb/s
    Stream #2:0(und): Video: h264 (High) (avc1 / 0x31637661), yuv420p, 640x360, 48 kb/s, 60 fps, 60 tbr, 15360 tbn, 120 tbc (default)
    Metadata:
      handler_name    : VideoHandler
    Stream #2:1(und): Audio: aac (LC) (mp4a / 0x6134706D), 48000 Hz, stereo, fltp, 192 kb/s (default)
    Metadata:
      handler_name    : SoundHandler
Input #3, mov,mp4,m4a,3gp,3g2,mj2, from 'cen.mp4':
  Metadata:
    major_brand     : isom
    minor_version   : 512
    compatible_brands: isomiso2avc1mp41
    encoder         : Lavf58.45.100
  Duration: 00:00:07.00, start: 0.000000, bitrate: 461 kb/s
    Stream #3:0(und): Video: h264 (High) (avc1 / 0x31637661), yuv420p, 640x360, 250 kb/s, 60 fps, 60 tbr, 15360 tbn, 120 tbc (default)
    Metadata:
      handler_name    : VideoHandler
    Stream #3:1(und): Audio: aac (LC) (mp4a / 0x6134706D), 48000 Hz, stereo, fltp, 196 kb/s (default)
    Metadata:
      handler_name    : SoundHandler
Input #4, mov,mp4,m4a,3gp,3g2,mj2, from 'cha.mp4':
  Metadata:
    major_brand     : isom
    minor_version   : 512
    compatible_brands: isomiso2avc1mp41
    encoder         : Lavf58.45.100
  Duration: 00:00:05.00, start: 0.000000, bitrate: 267 kb/s
    Stream #4:0(und): Video: h264 (High) (avc1 / 0x31637661), yuv420p, 640x360, 59 kb/s, 60 fps, 60 tbr, 15360 tbn, 120 tbc (default)
    Metadata:
      handler_name    : VideoHandler
    Stream #4:1(und): Audio: aac (LC) (mp4a / 0x6134706D), 48000 Hz, stereo, fltp, 194 kb/s (default)
    Metadata:
      handler_name    : SoundHandler
Input #5, mov,mp4,m4a,3gp,3g2,mj2, from 'grd.mp4':
  Metadata:
    major_brand     : isom
    minor_version   : 512
    compatible_brands: isomiso2avc1mp41
    encoder         : Lavf58.45.100
  Duration: 00:00:07.00, start: 0.000000, bitrate: 235 kb/s
    Stream #5:0(und): Video: h264 (High) (avc1 / 0x31637661), yuv420p, 640x360, 28 kb/s, 60 fps, 60 tbr, 15360 tbn, 120 tbc (default)
    Metadata:
      handler_name    : VideoHandler
    Stream #5:1(und): Audio: aac (LC) (mp4a / 0x6134706D), 48000 Hz, stereo, fltp, 193 kb/s (default)
    Metadata:
      handler_name    : SoundHandler
Input #6, mov,mp4,m4a,3gp,3g2,mj2, from 'grm.mp4':
  Metadata:
    major_brand     : isom
    minor_version   : 512
    compatible_brands: isomiso2avc1mp41
    encoder         : Lavf58.45.100
  Duration: 00:00:09.00, start: 0.000000, bitrate: 294 kb/s
    Stream #6:0(und): Video: h264 (High) (avc1 / 0x31637661), yuv420p, 640x360, 86 kb/s, 60 fps, 60 tbr, 15360 tbn, 120 tbc (default)
    Metadata:
      handler_name    : VideoHandler
    Stream #6:1(und): Audio: aac (LC) (mp4a / 0x6134706D), 48000 Hz, stereo, fltp, 195 kb/s (default)
    Metadata:
      handler_name    : SoundHandler
Input #7, mov,mp4,m4a,3gp,3g2,mj2, from 'htv.mp4':
  Metadata:
    major_brand     : isom
    minor_version   : 512
    compatible_brands: isomiso2avc1mp41
    encoder         : Lavf58.45.100
  Duration: 00:00:12.01, start: 0.000000, bitrate: 238 kb/s
    Stream #7:0(und): Video: h264 (High) (avc1 / 0x31637661), yuv420p, 640x360, 29 kb/s, 60 fps, 60 tbr, 15360 tbn, 120 tbc (default)
    Metadata:
      handler_name    : VideoHandler
    Stream #7:1(und): Audio: aac (LC) (mp4a / 0x6134706D), 48000 Hz, stereo, fltp, 196 kb/s (default)
    Metadata:
      handler_name    : SoundHandler
Input #8, mov,mp4,m4a,3gp,3g2,mj2, from 'lwt.mp4':
  Metadata:
    major_brand     : isom
    minor_version   : 512
    compatible_brands: isomiso2avc1mp41
    encoder         : Lavf58.45.100
  Duration: 00:00:10.00, start: 0.000000, bitrate: 239 kb/s
    Stream #8:0(und): Video: h264 (High) (avc1 / 0x31637661), yuv420p, 640x360, 30 kb/s, 60 fps, 60 tbr, 15360 tbn, 120 tbc (default)
    Metadata:
      handler_name    : VideoHandler
    Stream #8:1(und): Audio: aac (LC) (mp4a / 0x6134706D), 48000 Hz, stereo, fltp, 195 kb/s (default)
    Metadata:
      handler_name    : SoundHandler
Input #9, mov,mp4,m4a,3gp,3g2,mj2, from 'sou.mp4':
  Metadata:
    major_brand     : isom
    minor_version   : 512
    compatible_brands: isomiso2avc1mp41
    encoder         : Lavf58.45.100
  Duration: 00:00:08.00, start: 0.000000, bitrate: 247 kb/s
    Stream #9:0(und): Video: h264 (High) (avc1 / 0x31637661), yuv420p, 640x360, 39 kb/s, 60 fps, 60 tbr, 15360 tbn, 120 tbc (default)
    Metadata:
      handler_name    : VideoHandler
    Stream #9:1(und): Audio: aac (LC) (mp4a / 0x6134706D), 48000 Hz, stereo, fltp, 194 kb/s (default)
    Metadata:
      handler_name    : SoundHandler
Input #10, mov,mp4,m4a,3gp,3g2,mj2, from 'stv.mp4':
  Metadata:
    major_brand     : isom
    minor_version   : 512
    compatible_brands: isomiso2avc1mp41
    encoder         : Lavf58.45.100
  Duration: 00:00:09.00, start: 0.000000, bitrate: 257 kb/s
    Stream #10:0(und): Video: h264 (High) (avc1 / 0x31637661), yuv420p, 640x360, 51 kb/s, 60 fps, 60 tbr, 15360 tbn, 120 tbc (default)
    Metadata:
      handler_name    : VideoHandler
    Stream #10:1(und): Audio: aac (LC) (mp4a / 0x6134706D), 48000 Hz, stereo, fltp, 192 kb/s (default)
    Metadata:
      handler_name    : SoundHandler
Input #11, mov,mp4,m4a,3gp,3g2,mj2, from 'tha.mp4':
  Metadata:
    major_brand     : isom
    minor_version   : 512
    compatible_brands: isomiso2avc1mp41
    encoder         : Lavf58.45.100
  Duration: 00:00:06.00, start: 0.000000, bitrate: 454 kb/s
    Stream #11:0(und): Video: h264 (High) (avc1 / 0x31637661), yuv420p, 640x360, 245 kb/s, 60 fps, 60 tbr, 15360 tbn, 120 tbc (default)
    Metadata:
      handler_name    : VideoHandler
    Stream #11:1(und): Audio: aac (LC) (mp4a / 0x6134706D), 48000 Hz, stereo, fltp, 194 kb/s (default)
    Metadata:
      handler_name    : SoundHandler
Input #12, mov,mp4,m4a,3gp,3g2,mj2, from 'ttt.mp4':
  Metadata:
    major_brand     : isom
    minor_version   : 512
    compatible_brands: isomiso2avc1mp41
    encoder         : Lavf58.45.100
  Duration: 00:00:10.01, start: 0.000000, bitrate: 258 kb/s
    Stream #12:0(und): Video: h264 (High) (avc1 / 0x31637661), yuv420p, 640x360, 51 kb/s, 60 fps, 60 tbr, 15360 tbn, 120 tbc (default)
    Metadata:
      handler_name    : VideoHandler
    Stream #12:1(und): Audio: aac (LC) (mp4a / 0x6134706D), 48000 Hz, stereo, fltp, 193 kb/s (default)
    Metadata:
      handler_name    : SoundHandler
Input #13, mov,mp4,m4a,3gp,3g2,mj2, from 'utv.mp4':
  Metadata:
    major_brand     : isom
    minor_version   : 512
    compatible_brands: isomiso2avc1mp41
    encoder         : Lavf58.45.100
  Duration: 00:00:08.00, start: 0.000000, bitrate: 443 kb/s
    Stream #13:0(und): Video: h264 (High) (avc1 / 0x31637661), yuv420p, 640x360, 234 kb/s, 60 fps, 60 tbr, 15360 tbn, 120 tbc (default)
    Metadata:
      handler_name    : VideoHandler
    Stream #13:1(und): Audio: aac (LC) (mp4a / 0x6134706D), 48000 Hz, stereo, fltp, 194 kb/s (default)
    Metadata:
      handler_name    : SoundHandler
Input #14, mov,mp4,m4a,3gp,3g2,mj2, from 'wtv.mp4':
  Metadata:
    major_brand     : isom
    minor_version   : 512
    compatible_brands: isomiso2avc1mp41
    encoder         : Lavf58.45.100
  Duration: 00:00:08.00, start: 0.000000, bitrate: 431 kb/s
    Stream #14:0(und): Video: h264 (High) (avc1 / 0x31637661), yuv420p, 640x360, 224 kb/s, 60 fps, 60 tbr, 15360 tbn, 120 tbc (default)
    Metadata:
      handler_name    : VideoHandler
    Stream #14:1(und): Audio: aac (LC) (mp4a / 0x6134706D), 48000 Hz, stereo, fltp, 194 kb/s (default)
    Metadata:
      handler_name    : SoundHandler
Input #15, mov,mp4,m4a,3gp,3g2,mj2, from 'ytv.mp4':
  Metadata:
    major_brand     : isom
    minor_version   : 512
    compatible_brands: isomiso2avc1mp41
    encoder         : Lavf58.45.100
  Duration: 00:00:08.00, start: 0.000000, bitrate: 332 kb/s
    Stream #15:0(und): Video: h264 (High) (avc1 / 0x31637661), yuv420p, 640x360, 123 kb/s, 60 fps, 60 tbr, 15360 tbn, 120 tbc (default)
    Metadata:
      handler_name    : VideoHandler
    Stream #15:1(und): Audio: aac (LC) (mp4a / 0x6134706D), 48000 Hz, stereo, fltp, 195 kb/s (default)
    Metadata:
      handler_name    : SoundHandler
File 'output.mp4' already exists. Overwrite? [y/N] y
Stream mapping:
  Stream #0:0 (h264) -> scale
  Stream #0:1 (aac) -> amerge:in0
  Stream #1:0 (h264) -> scale
  Stream #1:1 (aac) -> amerge:in1
  Stream #2:0 (h264) -> scale
  Stream #2:1 (aac) -> amerge:in2
  Stream #3:0 (h264) -> scale
  Stream #3:1 (aac) -> amerge:in3
  Stream #4:0 (h264) -> scale
  Stream #4:1 (aac) -> amerge:in4
  Stream #5:0 (h264) -> scale
  Stream #5:1 (aac) -> amerge:in5
  Stream #6:0 (h264) -> scale
  Stream #6:1 (aac) -> amerge:in6
  Stream #7:0 (h264) -> scale
  Stream #7:1 (aac) -> amerge:in7
  Stream #8:0 (h264) -> scale
  Stream #8:1 (aac) -> amerge:in8
  Stream #9:0 (h264) -> scale
  Stream #9:1 (aac) -> amerge:in9
  Stream #10:0 (h264) -> scale
  Stream #10:1 (aac) -> amerge:in10
  Stream #11:0 (h264) -> scale
  Stream #11:1 (aac) -> amerge:in11
  Stream #12:0 (h264) -> scale
  Stream #12:1 (aac) -> amerge:in12
  Stream #13:0 (h264) -> scale
  Stream #13:1 (aac) -> amerge:in13
  Stream #14:0 (h264) -> scale
  Stream #14:1 (aac) -> amerge:in14
  Stream #15:0 (h264) -> scale
  Stream #15:1 (aac) -> amerge:in15
  xstack -> Stream #0:0 (libx264)
  amerge -> Stream #0:1 (aac)
Press [q] to stop, [?] for help
[Parsed_amerge_17 @ 0x558494cd1180] No channel layout for input 1
[Parsed_amerge_17 @ 0x558494cd1180] Input channel layouts overlap: output layout will be determined by the number of distinct input channels
[auto_resampler_16 @ 0x558494ce5fc0] [SWR @ 0x558494e3cb40] Input channel layout '32 channels (FL+FR+FC+LFE+BL+BR+FLC+FRC+BC+SL+SR+TC+TFL+TFC+TFR+TBL+TBC+TBR+DL+DR+WL)' is not supported
[auto_resampler_16 @ 0x558494ce5fc0] Failed to configure output pad on auto_resampler_16
Error reinitializing filters!
Failed to inject frame into filter network: Invalid argument
Error while processing the decoded data for stream #15:0
Conversion failed!

使用其他选项代替该调用，例如:

[0][over] overlay=0:0[v];[0][1][2][3][4][5][6][7][8][9][10][11][12][13][14][15]amix[a]

产生:

[AVFilterGraph @ 0x55ddeb2032c0] Too many inputs specified for the "amix" filter.
Error initializing complex filters.
Invalid argument

我已经在这方面搜索了几个 SO 页面 - 许多页面都提供了来自 @llogan、@Gyan 和其他专家的稍微不同的问题的解决方案 - 但不幸的是，没有一个有效。
毫无疑问，解决方案非常明显，但对我来说不是!有人可以帮忙吗？如果可以的话，我将不胜感激。

Answer 1

改用 join 或 amix 过滤器
join :

ffmpeg -i a.mp4 -i b.mp4 -i c.mp4 -i d.mp4 -i e.mp4 -i f.mp4 -i g.mp4 -i h.mp4 -i i.mp4 -i j.mp4 -i k.mp4 -i l.mp4 -i m.mp4 -i n.mp4 -i o.mp4 -i q.mp4 -i p.mp4 \
 -filter_complex \
 "[0:v]scale=iw/4:-1[v0];[1:v]scale=iw/4:-1[v1];[2:v]scale=iw/4:-1[v2]; \ 
  [3:v]scale=iw/4:-1[v3];[4:v]scale=iw/4:-1[v4];[5:v]scale=iw/4:-1[v5]; \
  [6:v]scale=iw/4:-1[v6];[7:v]scale=iw/4:-1[v7];[8:v]scale=iw/4:-1[v8]; \ 
  [9:v]scale=iw/4:-1[v9];[10:v]scale=iw/4:-1[v10];[11:v]scale=iw/4:-1[v11]; \
  [12:v]scale=iw/4:-1[v12];[13:v]scale=iw/4:-1[v13];[14:v]scale=iw/4:-1[v14]; \ 
  [15:v]scale=iw/4:-1[v15]; \
  [v0][v1][v2][v3][v4][v5][v6][v7][v8][v9][v10][v11][v12][v13][v14][v15]xstack=inputs=16:layout=0_0|w0_0|w0+w1_0|w0+w1+w2_0|0_h0|w4_h0|w4+w5_h0|w4+w5+w6_h0|0_h0+h4|w8_h0+h4|w8+w9_h0+h4|w8+w9+w10_h0+h4|0_h0+h4+h8|w12_h0+h4+h8|w12+w13_h0+h4+h8|w12+w13+w14_h0+h4+h8; \
  [0:a][1:a][2:a][3:a][4:a][5:a][6:a][7:a][8:a][9:a][10:a][11:a][12:a][13:a][14:a][15:a]join=inputs=16" \
output.mp4

amix :
amix 默认为 inputs=2 , 所以添加 inputs=16 .

ffmpeg -i a.mp4 -i b.mp4 -i c.mp4 -i d.mp4 -i e.mp4 -i f.mp4 -i g.mp4 -i h.mp4 -i i.mp4 -i j.mp4 -i k.mp4 -i l.mp4 -i m.mp4 -i n.mp4 -i o.mp4 -i q.mp4 -i p.mp4 \
 -filter_complex \
 "[0:v]scale=iw/4:-1[v0];[1:v]scale=iw/4:-1[v1];[2:v]scale=iw/4:-1[v2]; \ 
  [3:v]scale=iw/4:-1[v3];[4:v]scale=iw/4:-1[v4];[5:v]scale=iw/4:-1[v5]; \
  [6:v]scale=iw/4:-1[v6];[7:v]scale=iw/4:-1[v7];[8:v]scale=iw/4:-1[v8]; \ 
  [9:v]scale=iw/4:-1[v9];[10:v]scale=iw/4:-1[v10];[11:v]scale=iw/4:-1[v11]; \
  [12:v]scale=iw/4:-1[v12];[13:v]scale=iw/4:-1[v13];[14:v]scale=iw/4:-1[v14]; \ 
  [15:v]scale=iw/4:-1[v15]; \
  [v0][v1][v2][v3][v4][v5][v6][v7][v8][v9][v10][v11][v12][v13][v14][v15]xstack=inputs=16:layout=0_0|w0_0|w0+w1_0|w0+w1+w2_0|0_h0|w4_h0|w4+w5_h0|w4+w5+w6_h0|0_h0+h4|w8_h0+h4|w8+w9_h0+h4|w8+w9+w10_h0+h4|0_h0+h4+h8|w12_h0+h4+h8|w12+w13_h0+h4+h8|w12+w13+w14_h0+h4+h8; \
  [0:a][1:a][2:a][3:a][4:a][5:a][6:a][7:a][8:a][9:a][10:a][11:a][12:a][13:a][14:a][15:a]amix=inputs=16" \
output.mp4