ffmpeg concat垂直视频，不同尺寸

如何解决ffmpeg concat垂直视频，不同尺寸

上下文： 3个输入视频：

foo.mov：1080x1920（垂直，非水平），带有音频。

bar.mp4和fiz.mp4：480x360，带有音频。 （注意：.mp4与.mov不同）

目标：合并所有3个视频。输出out.mp4应该是480x360。挤压foo.mov，但保持其宽高比，占据100％的高度，但是细长的视频应仅位于中间，左右两侧均为黑色（或其他颜色）空白。 foo.mov不应被裁剪。

我目前在下面有此命令（添加了换行符以便更好地显示），但需要在PLACEHOLDER1处填充缺少的代码以生成v0，例如v0如上所述将其调整为480x360。如果到目前为止我的尝试是正确的，请帮助完成PLACEHOLDER1;否则，请提供一个更好的解决方案有解释。

ffmpeg 
-r 24 -i foo.mov 
-r 24 -i bar.mp4 
-r 24 -i fiz.mp4
-filter_complex 
"[0:v] PLACEHOLDER1 [v0];
[v0][1][2] concat=n=3:v=1:a=1 [v][a]" 
-map "[v]" -map "[a]" out.mp4

运行

ffmpeg -n -i foo.MOV -i bar.mp4 -i fiz.mp4

提供此信息：

ffmpeg version 4.3.1 Copyright (c) 2000-2020 the FFmpeg developers
  built with Apple clang version 11.0.3 (clang-1103.0.32.62)
  [...configuration omitted...]
  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 'foo.MOV':
  Metadata:
    major_brand     : qt  
    minor_version   : 0
    compatible_brands: qt  
    creation_time   : [omitted]
    com.apple.quicktime.make: [omitted]
    com.apple.quicktime.model: [omitted]
    com.apple.quicktime.software: [omitted]
    com.apple.quicktime.creationdate: [omitted]
  Duration: 00:00:04.71,start: 0.000000,bitrate: 17579 kb/s
    Stream #0:0(und): Video: h264 (High) (avc1 / 0x31637661),yuv420p(tv,bt709),1920x1080,17492 kb/s,24 fps,24 tbr,600 tbn,1200 tbc (default)
    Metadata:
      rotate          : 90
      creation_time   : [omitted]
      handler_name    : Core Media Video
      encoder         : H.264
    Side data:
      displaymatrix: rotation of -90.00 degrees
    Stream #0:1(und): Audio: aac (LC) (mp4a / 0x6134706D),44100 Hz,mono,fltp,63 kb/s (default)
    Metadata:
      creation_time   : [omitted]
      handler_name    : Core Media Audio
    Stream #0:2(und): Data: none (mebx / 0x7862656D),9 kb/s (default)
    Metadata:
      creation_time   : [omitted]
      handler_name    : Core Media Metadata
    Stream #0:3(und): Data: none (mebx / 0x7862656D),0 kb/s (default)
    Metadata:
      creation_time   : [omitted]
      handler_name    : Core Media Metadata

Input #1,from 'bar.mp4':
  Metadata:
    major_brand     : isom
    minor_version   : 512
    compatible_brands: isomiso2avc1mp41
    encoder         : Lavf58.29.100
  Duration: 00:00:01.94,bitrate: 641 kb/s
    Stream #1:0(und): Video: h264 (High) (avc1 / 0x31637661),smpte170m/unknown/smpte170m),480x360 [SAR 1:1 DAR 4:3],354 kb/s,24.58 fps,24.58 tbr,113734695.00 tbn,49.16 tbc (default)
    Metadata:
      handler_name    : VideoHandler
    Stream #1:1(und): Audio: aac (LC) (mp4a / 0x6134706D),48000 Hz,stereo,280 kb/s (default)
    Metadata:
      handler_name    : SoundHandler
      
Input #2,from 'fiz.mp4':
  Metadata:
    major_brand     : isom
    minor_version   : 512
    compatible_brands: isomiso2avc1mp41
    encoder         : Lavf58.29.100
  Duration: 00:00:01.98,bitrate: 725 kb/s
    Stream #2:0(und): Video: h264 (High) (avc1 / 0x31637661),442 kb/s,49.16 tbc (default)
    Metadata:
      handler_name    : VideoHandler
    Stream #2:1(und): Audio: aac (LC) (mp4a / 0x6134706D),278 kb/s (default)
    Metadata:
      handler_name    : SoundHandler