Audio FFmpeg音频通道rematrix（5.1至立体声）

我有一个（非常大！）Apple ProRes 422文件，带有16通道音频。为了能够在功能较弱的计算机上使用它，我想将其转换为标准MP4文件（h264视频编解码器、立体声音频）。然而，原始文件有16个音频通道，当我试图转换它时，FFmpeg会给出一个错误（“需要Rematrix”）。如何重新组合音频频道？是否需要其他步骤

这是我使用的FFmpeg命令：

ffmpeg -y -i Capture0000.mov -vcodec libx264 -vb 2000k -pix_fmt yuv420p -coder 0 -profile:v baseline -acodec libfaac -ab 128k /tmp/out.mp4

这是FFmpeg输出：

ffmpeg version 2.2.git Copyright (c) 2000-2014 the FFmpeg developers
      built on May  8 2014 14:17:45 with gcc 4.6 (Ubuntu/Linaro 4.6.3-1ubuntu5)
      configuration: --prefix=/usr/local/ffmpeg_build --extra-cflags=-I/usr/local/ffmpeg_build/include --extra-ldflags=-L/usr/local/ffmpeg_build/lib --bindir=/usr/local/bin --extra-libs=-ldl --enable-gpl --enable-libass --enable-libfdk-aac --enable-libfreetype --enable-libmp3lame --enable-libopus --enable-libtheora --enable-libvorbis --enable-libvpx --enable-libx264 --enable-nonfree --enable-x11grab --enable-libxvid --enable-libfaac
      libavutil      52. 81.100 / 52. 81.100
      libavcodec     55. 60.103 / 55. 60.103
      libavformat    55. 37.102 / 55. 37.102
      libavdevice    55. 13.101 / 55. 13.101
      libavfilter     4.  5.100 /  4.  5.100
      libswscale      2.  6.100 /  2.  6.100
      libswresample   0. 18.100 /  0. 18.100
      libpostproc    52.  3.100 / 52.  3.100
    Input #0, mov,mp4,m4a,3gp,3g2,mj2, from 'Capture0000.mov':
      Metadata:
        creation_time   : 2014-08-17 18:30:31
      Duration: 01:01:22.52, start: 0.000000, bitrate: 202001 kb/s
        Stream #0:0(eng): Video: prores (apch / 0x68637061), yuv422p10le, 1920x1080, 183513 kb/s, SAR 1:1 DAR 16:9, 25 fps, 25 tbr, 2500 tbn, 2500 tbc (default)
        Metadata:
          creation_time   : 2014-08-17 18:30:31
          handler_name    : Apple Alias Data Handler
          encoder         : Apple ProRes 422 (HQ)
        Stream #0:1(eng): Audio: pcm_s24le (lpcm / 0x6D63706C), 48000 Hz, 16 channels, s32, 18432 kb/s (default)
        Metadata:
          creation_time   : 2014-08-17 18:30:31
          handler_name    : Apple Alias Data Handler
    [auto-inserted resampler 0 @ 0x3943da0] [SWR @ 0x39441a0] Rematrix is needed between 16 channels and 5.1 but there is not enough information to do it
    [auto-inserted resampler 0 @ 0x3943da0] Failed to configure output pad on auto-inserted resampler 0
    Error opening filters!

这是FFprobe输出：

ffprobe version 2.2.git Copyright (c) 2007-2014 the FFmpeg developers
  built on May  8 2014 14:17:45 with gcc 4.6 (Ubuntu/Linaro 4.6.3-1ubuntu5)
  configuration: --prefix=/usr/local/ffmpeg_build --extra-cflags=-I/usr/local/ffmpeg_build/include --extra-ldflags=-L/usr/local/ffmpeg_build/lib --bindir=/usr/local/bin --extra-libs=-ldl --enable-gpl --enable-libass --enable-libfdk-aac --enable-libfreetype --enable-libmp3lame --enable-libopus --enable-libtheora --enable-libvorbis --enable-libvpx --enable-libx264 --enable-nonfree --enable-x11grab --enable-libxvid --enable-libfaac
  libavutil      52. 81.100 / 52. 81.100
  libavcodec     55. 60.103 / 55. 60.103
  libavformat    55. 37.102 / 55. 37.102
  libavdevice    55. 13.101 / 55. 13.101
  libavfilter     4.  5.100 /  4.  5.100
  libswscale      2.  6.100 /  2.  6.100
  libswresample   0. 18.100 /  0. 18.100
  libpostproc    52.  3.100 / 52.  3.100
Input #0, mov,mp4,m4a,3gp,3g2,mj2, from 'Capture0000.mov':
  Metadata:
    creation_time   : 2014-08-17 18:30:31
  Duration: 01:01:22.52, start: 0.000000, bitrate: 202001 kb/s
    Stream #0:0(eng): Video: prores (apch / 0x68637061), yuv422p10le, 1920x1080, 183513 kb/s, SAR 1:1 DAR 16:9, 25 fps, 25 tbr, 2500 tbn, 2500 tbc (default)
    Metadata:
      creation_time   : 2014-08-17 18:30:31
      handler_name    : Apple Alias Data Handler
      encoder         : Apple ProRes 422 (HQ)
    Stream #0:1(eng): Audio: pcm_s24le (lpcm / 0x6D63706C), 48000 Hz, 16 channels, s32, 18432 kb/s (default)
    Metadata:
      creation_time   : 2014-08-17 18:30:31
      handler_name    : Apple Alias Data Handler

---

找到了！仅提取音频后，发现前两个通道是立体声，其余四个通道是空的，因此我添加了以下内容：

-af 'pan=stereo:c0=FL:c1=FR'

它只使用左前和右前声道进行立体声混音

编辑：较新版本的FFMpeg需要使用|而不是：，因此应该是这样

stereo|c0=FL|c1=FR