ffmpeg安装

在ffmpeg安装中碰到两种报错，需要注意两点：

1. 用conda -c conda-forge安装，避免Unknown encoder 'libx264’报错
2. 安装ffmpeg-python，而不是ffmpeg

conda install -c conda-forge ffmpeg-python

此外，用于查看libx264编码存不存在的命令：

jbhansen@craven-moorhead:~$ ffmpeg -encoders | grep 264
ffmpeg version 3.2.4 Copyright (c) 2000-2017 the FFmpeg developers
  built with gcc 5.5.0 (GCC)
  configuration: --prefix=/usr --libdir=/usr/lib64 --shlibdir=/usr/lib64 --docdir=/usr/doc/ffmpeg-3.2.4/html --mandir=/usr/man --disable-debug --enable-shared --disable-static --enable-gpl --enable-version3 --enable-avresample --arch=x86_64 --enable-nonfree --enable-libschroedinger --enable-libfdk-aac --enable-libfontconfig --enable-libfreetype --enable-libfribidi --enable-gnutls --enable-libass --enable-libcaca --enable-libcdio --enable-libdc1394 --enable-frei0r --enable-libgme --enable-libiec61883 --enable-libilbc --enable-openal --enable-libopus --enable-librtmp --enable-libsnappy --enable-libspeex --enable-libssh --enable-libtheora --enable-libtwolame --enable-libv4l2 --enable-libvidstab --enable-libvorbis --enable-libvpx --enable-libwebp --enable-libx264 --enable-libx265 --enable-libxvid --enable-libmp3lame --enable-libopencore-amrnb --enable-libopencore-amrwb --enable-opengl --enable-libopenjpeg --enable-libpulse --enable-libsmbclient --enable-openssl --enable-libwavpack --enable-x11grab
  libavutil      55. 34.101 / 55. 34.101
  libavcodec     57. 64.101 / 57. 64.101
  libavformat    57. 56.101 / 57. 56.101
  libavdevice    57.  1.100 / 57.  1.100
  libavfilter     6. 65.100 /  6. 65.100
  libavresample   3.  1.  0 /  3.  1.  0
  libswscale      4.  2.100 /  4.  2.100
  libswresample   2.  3.100 /  2.  3.100
  libpostproc    54.  1.100 / 54.  1.100
 V..... libx264              libx264 H.264 / AVC / MPEG-4 AVC / MPEG-4 part 10 (codec h264)
 V..... libx264rgb           libx264 H.264 / AVC / MPEG-4 AVC / MPEG-4 part 10 RGB (codec h264)
 V..... h264_nvenc           NVIDIA NVENC H.264 encoder (codec h264)
 V..... h264_vaapi           H.264/AVC (VAAPI) (codec h264)
 V..... nvenc                NVIDIA NVENC H.264 encoder (codec h264)
 V..... nvenc_h264           NVIDIA NVENC H.264 encoder (codec h264)