The Matroska muxer does not yet support muxing cook

在使用FFmpeg进行视频合并的时候报错：

ffmpeg version 4.4 Copyright (c) 2000-2021 the FFmpeg developers
  built with Apple clang version 12.0.0 (clang-1200.0.32.29)
  configuration: --prefix=/usr/local/Cellar/ffmpeg/4.4_2 --enable-shared --enable-pthreads --enable-version3 --cc=clang --host-cflags= --host-ldflags= --enable-ffplay --enable-gnutls --enable-gpl --enable-libaom --enable-libbluray --enable-libdav1d --enable-libmp3lame --enable-libopus --enable-librav1e --enable-librubberband --enable-libsnappy --enable-libsrt --enable-libtesseract --enable-libtheora --enable-libvidstab --enable-libvorbis --enable-libvpx --enable-libwebp --enable-libx264 --enable-libx265 --enable-libxml2 --enable-libxvid --enable-lzma --enable-libfontconfig --enable-libfreetype --enable-frei0r --enable-libass --enable-libopencore-amrnb --enable-libopencore-amrwb --enable-libopenjpeg --enable-libspeex --enable-libsoxr --enable-libzmq --enable-libzimg --disable-libjack --disable-indev=jack --enable-avresample --enable-videotoolbox
  libavutil      56. 70.100 / 56. 70.100
  libavcodec     58.134.100 / 58.134.100
  libavformat    58. 76.100 / 58. 76.100
  libavdevice    58. 13.100 / 58. 13.100
  libavfilter     7.110.100 /  7.110.100
  libavresample   4.  0.  0 /  4.  0.  0
  libswscale      5.  9.100 /  5.  9.100
  libswresample   3.  9.100 /  3.  9.100
  libpostproc    55.  9.100 / 55.  9.100
[rm @ 0x7f8b03018000] Invalid stream index 2 for index at pos 83519036
Input #0, concat, from '1.txt':
  Duration: N/A, start: 0.000000, bitrate: 225 kb/s
  Stream #0:0: Video: rv40 (RV40 / 0x30345652), yuv420p, 352x288, 180 kb/s, 25 fps, 25 tbr, 1k tbn, 1k tbc
  Stream #0:1: Audio: cook (cook / 0x6B6F6F63), 44100 Hz, stereo, fltp, 44 kb/s
[matroska @ 0x7f8b02847c00] The Matroska muxer does not yet support muxing cook
Could not write header for output file #0 (incorrect codec parameters ?): Not yet implemented in FFmpeg, patches welcome
Error initializing output stream 0:1 -- 
Stream mapping:
  Stream #0:0 -> #0:0 (copy)
  Stream #0:1 -> #0:1 (copy)
    Last message repeated 1 times

解决方法：

两种，一种是将mkv改为rm

第二种是-c改为-c:v

推荐第二种