macos安装ffmpeg以及出现问题的解决方案，一次成功

安装ffmpeg使用brew
首先安装brew：

/usr/bin/ruby -e "$(curl -fsSL https://raw.githubusercontent.com/Homebrew/install/master/install)"

出现这个：==> Installation successful!安装成功

....

No changes to formulae.
==> Installation successful!

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  https://docs.brew.sh/Analytics

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- Run `brew help` to get started
- Further documentation: 
    https://docs.brew.sh

看看相关命令

$ brew
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  brew search [TEXT|/REGEX/]
  brew info [FORMULA...]
  brew install FORMULA...
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  brew config
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  brew create [URL [--no-fetch]]
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Further help:
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安装ffmpeg，使用brew安装：

$ brew install  ffmpeg 
==> Installing dependencies for ffmpeg: frei0r, libtasn1, nettle, p11-kit, openssl, libevent, unbound, gnutls, lame, fribidi, gettext, python, glib, lzo, pixman, cairo, graphite2, icu4c, harfbuzz, libass, libbluray, libsoxr, libogg, libvorbis, libvpx, opencore-amr, opus, flac, libsndfile, libsamplerate, rubberband, sdl2, snappy, speex, webp, theora, x264, x265 and xvid
==> Installing ffmpeg dependency: frei0r
==> Downloading https://homebrew.bintray.com/bottles/frei0r-1.6.1.mojave.bottle.1.tar.gz
==> Downloading from https://akamai.bintray.com/a5/a509ee11dc4a3cd431a888c708d32c53d81e5ca67250520f91284d4370d946d4?__gda__=exp=1563528408~hmac=dd80d6bc9693a885841309c5bc094e71743
######################################################################## 100.0%
==> Pouring frei0r-1.6.1.mojave.bottle.1.tar.gz