我正在创建我自己的MKV视频，当我使用Python 3.11.2的子进程模块执行FFmpeg命令时，我发现了一个奇怪的错误。
我的FFmpeg命令在终端中运行良好（以成功结束）：

ffmpeg -y \
-i input_video_stream.mkv \
-i input_audio_stream_1.ac3 \
-i input_audio_stream_2.ac3 \
-i input_audio_stream_3.ac3 \
-i input_audio_stream_4.ac3 \
-f srt -i input_subtitle_stream_1.srt \
-f srt -i input_subtitle_stream_2.srt \
-map 0 -map 1 -map 2 -map 3 -map 4 -map 5 -map 6 \
-c copy \
-metadata:s:a:0 language=eng -metadata:s:a:0 title="English1" \
-metadata:s:a:1 language=eng -metadata:s:a:1 title="English2" \
-metadata:s:a:2 language=eng -metadata:s:a:2 title="English3" \
-metadata:s:a:3 language=eng -metadata:s:a:3 title="English4" \
-metadata:s:s:0 language=eng -metadata:s:s:0 title="English1" -metadata:s:s:0 mimetype=application/x-ass \
-metadata:s:s:1 language=eng -metadata:s:s:1 title="English2" -metadata:s:s:1 mimetype=application/x-ass \
-disposition:a:0 default -disposition:s:s:0 default \
output_video_with_audio_and_subtitles.mkv

但是当我在同一个终端（同一个会话和同一个ffmpeg版本）通过python从subprocess.run（命令）运行它时：

subprocess.run([
    'ffmpeg', '-y',
    '-i', 'input_video_stream.mkv',
    '-i', 'input_audio_stream_1.ac3',
    '-i', 'input_audio_stream_2.ac3',
    '-i', 'input_audio_stream_3.ac3',
    '-i', 'input_audio_stream_4.ac3',
    '-f', 'srt', '-i', 'input_subtitle_stream_1.srt',
    '-f', 'srt', '-i', 'input_subtitle_stream_2.srt',
    '-map', '0', '-map', '1', '-map', '2', '-map', '3', '-map', '4', '-map', '5', '-map', '6',
    '-c', 'copy',
    '-metadata:s:a:0', 'language=eng', '-metadata:s:a:0', 'title="English1"', 
    '-metadata:s:a:1', 'language=eng', '-metadata:s:a:1', 'title="English2"', 
    '-metadata:s:a:2', 'language=eng', '-metadata:s:a:2', 'title="English3"', 
    '-metadata:s:a:3', 'language=eng', '-metadata:s:a:3', 'title="English4"', 
    '-metadata:s:s:0', 'language=eng', '-metadata:s:s:0', 'title="English1"', 
    '-metadata:s:s:0', 'mimetype=application/x-ass',
    '-metadata:s:s:1', 'language=eng', '-metadata:s:s:1', 'title="English2"', '-metadata:s:s:1', 'mimetype=application/x-ass', 
    '-disposition:a:0 default', '-disposition:s:s:0 default', 
    'output_video_with_audio_and_subtitles.mkv'
])

它失败了：

ffmpeg version 5.1.2-3 Copyright (c) 2000-2022 the FFmpeg developers
  built with gcc 12 (Debian 12.2.0-14)
  configuration: --prefix=/usr --extra-version=3 --toolchain=hardened --libdir=/usr/lib/x86_64-linux-gnu --incdir=/usr/include/x86_64-linux-gnu --arch=amd64 --enable-gpl --disable-stripping --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-libglslang --enable-libgme --enable-libgsm --enable-libjack --enable-libmp3lame --enable-libmysofa --enable-libopenjpeg --enable-libopenmpt --enable-libopus --enable-libpulse --enable-librabbitmq --enable-librist --enable-librubberband --enable-libshine --enable-libsnappy --enable-libsoxr --enable-libspeex --enable-libsrt --enable-libssh --enable-libsvtav1 --enable-libtheora --enable-libtwolame --enable-libvidstab --enable-libvorbis --enable-libvpx --enable-libwebp --enable-libx265 --enable-libxml2 --enable-libxvid --enable-libzimg --enable-libzmq --enable-libzvbi --enable-lv2 --enable-omx --enable-openal --enable-opencl --enable-opengl --enable-sdl2 --disable-sndio --enable-libjxl --enable-pocketsphinx --enable-librsvg --enable-libmfx --enable-libdc1394 --enable-libdrm --enable-libiec61883 --enable-chromaprint --enable-frei0r --enable-libx264 --enable-libplacebo --enable-librav1e --enable-shared
  libavutil      57. 28.100 / 57. 28.100
  libavcodec     59. 37.100 / 59. 37.100
  libavformat    59. 27.100 / 59. 27.100
  libavdevice    59.  7.100 / 59.  7.100
  libavfilter     8. 44.100 /  8. 44.100
  libswscale      6.  7.100 /  6.  7.100
  libswresample   4.  7.100 /  4.  7.100
  libpostproc    56.  6.100 / 56.  6.100
Input #0, matroska,webm, from 'input_video_stream.mkv':
  Metadata:
    ENCODER         : Lavf59.27.100
  Duration: 00:44:19.94, start: 0.000000, bitrate: 22551 kb/s
  Stream #0:0: Video: h264 (High), yuv420p(tv, bt709, progressive), 1920x1080 [SAR 1:1 DAR 16:9], 23.98 fps, 23.98 tbr, 1k tbn (default)
    Metadata:
      BPS             : 22549589
      NUMBER_OF_FRAMES: 63631
      NUMBER_OF_BYTES : 7480665638
      _STATISTICS_WRITING_APP: mkvmerge v56.0.0 ('Strasbourg / St. Denis') 64-bit
      _STATISTICS_WRITING_DATE_UTC: 2023-05-15 08:21:43
      _STATISTICS_TAGS: BPS DURATION NUMBER_OF_FRAMES NUMBER_OF_BYTES
      DURATION        : 00:44:19.942000000
[ac3 @ 0x55b374ee9e80] Estimating duration from bitrate, this may be inaccurate
Input #1, ac3, from 'input_audio_stream_1.ac3':
  Duration: 00:44:19.89, start: 0.000000, bitrate: 448 kb/s
  Stream #1:0: Audio: ac3, 48000 Hz, 5.1(side), fltp, 448 kb/s
[ac3 @ 0x55b37502ef80] Estimating duration from bitrate, this may be inaccurate
Input #2, ac3, from 'input_audio_stream_2.ac3':
  Duration: 00:44:19.89, start: 0.000000, bitrate: 192 kb/s
  Stream #2:0: Audio: ac3, 48000 Hz, stereo, fltp, 192 kb/s
[ac3 @ 0x55b374efc900] Estimating duration from bitrate, this may be inaccurate
Input #3, ac3, from 'input_audio_stream_3.ac3':
  Duration: 00:43:19.18, start: 0.000000, bitrate: 384 kb/s
  Stream #3:0: Audio: ac3, 48000 Hz, stereo, fltp, 384 kb/s
[ac3 @ 0x55b374fd60c0] Estimating duration from bitrate, this may be inaccurate
Input #4, ac3, from 'input_audio_stream_4.ac3':
  Duration: 00:43:19.18, start: 0.000000, bitrate: 192 kb/s
  Stream #4:0: Audio: ac3, 48000 Hz, stereo, fltp, 192 kb/s
Input #5, srt, from 'input_subtitle_stream_1.srt':
  Duration: N/A, bitrate: N/A
  Stream #5:0: Subtitle: subrip
Input #6, srt, from 'input_subtitle_stream_2.srt':
  Duration: N/A, bitrate: N/A
  Stream #6:0: Subtitle: subrip
[matroska @ 0x55b3751a1940] Invalid stream specifier: a:0 default.
    Last message repeated 1 times

我知道它正在报告音频（[matroska@0x55b3751a1940] Invalid stream specifier：a：0默认值。最后一条消息重复了1次），但它可能是我的ffmpeg命令的问题。