Mac OS上使用ffmpeg的「血淚」總結

時間 2019-11-05

原文原文鏈接

標題真不是誇張，這幾天在整理視頻相關的處理流程，爲了得到一些性能數據，打算在本身的MacBook Pro 上面裝ffmepg，這一折騰四、5天就過去了。有些問題，在解決以後就豁然開朗了，沒有解決以前，真的是百思不得其解，中間就好像隔着一層紗同樣。如今將這幾天的經歷記錄下來，一是方便本身後面查看，二是但願節省你們的時間。html

個人Mac OS版本是macOS Catalina 10.15.1，Xcode版本是11.1，安裝了Command Line Tools for Xcode 11 ，處理器是2 GHz 四核Intel Core i7，內存是8 GB 1600 MHz DDR3。git

首先須要說明一下，網上有些資料多是好久以前寫的，對應的Mac OS版本也比較早，之前能用的步驟的，如今可能就不行了。下面列舉幾個在個人機器上面不適用的場景，如有其餘人也遇到了，能夠參照一下，有時候能夠根據命令的執行錯誤信息去Google或者百度到解決辦法，有時候也可能會被帶到溝裏面去（我就是被帶到溝裏好幾天了）。github

直接用以下brew命令安裝ffmpeg，並用--with-帶上若干關聯的編碼解碼庫，這樣是不行的,若執行則會獲得錯誤信息「invalid option: --with-chromaprint」。

brew install ffmpeg --with-chromaprint --with-fdk-aac --with-fontconfig --with-freetype --with-frei0r --with-game-music-emu --with-libass --with-libbluray --with-libbs2b --with-libcaca --with-libgsm --with-libmodplug --with-librsvg --with-libsoxr --with-libssh --with-libvidstab --with-libvorbis --with-libvpx --with-opencore-amr --with-openh264 --with-openjpeg --with-openssl --with-opus --with-rtmpdump --with-rubberband --with-sdl2 --with-snappy --with-speex --with-tesseract --with-theora --with-tools --with-two-lame --with-wavpack --with-webp --with-x265 --with-xz --with-zeromq --with-zim
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用以下命令嘗試將input_file_name.mp4視頻從mpeg4制式(視頻是x264編碼，音頻是aac編碼)轉成webm制式（視頻是vp9編碼，音頻是opus編碼），是不行的，若執行則會獲得錯誤信息「Unknown decoder 'libx264'」、「Unrecognized option 'y '.」，根據此錯誤信息去找解決方案一樣會被帶到溝裏面去。

ffmpeg -y  -c:a libfdk_aac -c:v libx264 -i input_file_name.mp4 -c:v libvpx-vp9 -c:a libvorbis output_file_name.webm
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ffmpeg -y  -acodec libfdk_aac -vcodec libx264 -i input_file_name.mp4 -c:v libvpx-vp9 -c:a libvorbis output_file_name.webm
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官方文檔通常會有人去維護，出錯或者不兼容的可能性較低，出現問題後，通常首先須要想到去官方文檔（MacOS ffmpeg 官方文檔）查看解決辦法。我是搜了一下網上的參考資料，後面被折騰了好幾天，實在沒有辦法了，又去仔細看了一下官方文檔。上面介紹了三種方法，一是經過HomeBrew安裝，二是經過編譯好的靜態庫，三是經過ffmpeg源碼安裝。本文重點將經過HomeBrew的方式進行安裝，且通過實踐肯定是可行的，具體以下。 web

第一步，安裝Homebrew

Mac裏面經常使用的命令行包管理工具，經過以下命令執行安裝Homebrewruby

/usr/bin/ruby -e "$(curl -fsSL https://raw.githubusercontent.com/Homebrew/install/master/install)"
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第二步，安裝ffmpeg

執行bash

brew install ffmpeg
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或者執行均可以，惟一區別是下面語句安裝的是最新版本。app

brew install ffmpeg --HEAD
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二者都會檢測ffmpeg的依賴包並自動安裝上，請耐心等待，能夠用ps -ef | grep ffmpeg 看一下最新進展。上面兩步都沒有問題，好多博客也都這麼寫的，可是須要看清官方的下面表述「Since v2.0, Homebrew does not offer options for its core formulae anymore. Users who want to build ffmpeg with additional libraries (including non-free ones) need to use so-called taps from third party repositories. These repositories are not maintained by Homebrew」，簡單說一下就是「從brew的2.0版本開始，brew再也不提供針對ffmepg的options的一鍵關聯安裝了，若是須要將options和ffmpeg關聯起來的話，須要採用第三方的options倉庫」。個人brew版本以下，因此僅僅經過上面兩步來安裝ffmepg，是關聯不了諸如x264,vp9等視頻編解碼器的。若是有同窗也是這種狀況，須要注意一下。ssh

Homebrew 2.1.15
Homebrew/homebrew-core (git revision c10ec; last commit 2019-11-02)
Homebrew/homebrew-cask (git revision bd0e9; last commit 2019-11-02)
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第三步，選擇一個第三方倉庫，安裝options、並和ffmepg關聯起來。

有兩個倉庫，分別是homebrew-ffmpeg和varenc/homebrew-ffmpeg，我用的是第一個，有興趣的同窗能夠用第二個嘗試一下。curl

1）執行ide

brew tap homebrew-ffmpeg/ffmpeg
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2）執行

brew install homebrew-ffmpeg/ffmpeg/ffmpeg
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3）執行以下命令，看此倉庫支持哪些options。

brew options homebrew-ffmpeg/ffmpeg/ffmpeg
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4）根據第3）步獲得的options，替換下面命令中的option,而後執行

brew install homebrew-ffmpeg/ffmpeg/ffmpeg --with-<option1> --with-<option2> ...
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執行如上幾個步驟後，就成功的安裝好ffmepg及其依賴包，同時將ffmepg和許多編解碼庫關聯起來了。

第四步，實際操做幾個視頻驗證一下

以4K網站上面的一個4K視頻puppies-bath-in-4k爲例一、抽幀，每20秒抽一幀,操做耗時在34.87秒左右。

JAMESWHALE-MB2:Downloads james$ ffmpeg -i PUPPIES_BATH_IN_4K_Original_H.264_AAC.mp4 -f image2 -vf fps=fps=1/20 puppies_%d.png
ffmpeg version git-2019-11-01-53c21c2 Copyright (c) 2000-2019 the FFmpeg developers
  built with Apple clang version 11.0.0 (clang-1100.0.33.8)
  configuration: --prefix=/usr/local/Cellar/ffmpeg/HEAD-53c21c2_2 --enable-shared --enable-pthreads --enable-version3 --enable-avresample --cc=clang --host-cflags='-I/Library/Java/JavaVirtualMachines/jdk1.8.0_77.jdk/Contents/Home/include -I/Library/Java/JavaVirtualMachines/jdk1.8.0_77.jdk/Contents/Home/include/darwin -fno-stack-check' --host-ldflags= --enable-ffplay --enable-gnutls --enable-gpl --enable-libaom --enable-libbluray --enable-libmp3lame --enable-libopus --enable-librubberband --enable-libsnappy --enable-libtesseract --enable-libtheora --enable-libvidstab --enable-libvorbis --enable-libvpx --enable-libx264 --enable-libx265 --enable-libxvid --enable-lzma --enable-libfontconfig --enable-libfreetype --enable-frei0r --enable-libass --enable-libopencore-amrnb --enable-libopencore-amrwb --enable-libopenjpeg --enable-librtmp --enable-libspeex --enable-libsoxr --enable-videotoolbox --disable-libjack --disable-indev=jack
  libavutil      56. 35.101 / 56. 35.101
  libavcodec     58. 60.100 / 58. 60.100
  libavformat    58. 33.100 / 58. 33.100
  libavdevice    58.  9.100 / 58.  9.100
  libavfilter     7. 66.100 /  7. 66.100
  libavresample   4.  0.  0 /  4.  0.  0
  libswscale      5.  6.100 /  5.  6.100
  libswresample   3.  6.100 /  3.  6.100
  libpostproc    55.  6.100 / 55.  6.100
Input #0, mov,mp4,m4a,3gp,3g2,mj2, from 'PUPPIES_BATH_IN_4K_Original_H.264_AAC.mp4':
  Metadata:
    major_brand     : mp42
    minor_version   : 0
    compatible_brands: isommp42
    creation_time   : 2012-09-21T01:14:45.000000Z
  Duration: 00:02:29.63, start: 0.000000, bitrate: 21244 kb/s
    Stream #0:0(und): Video: h264 (High) (avc1 / 0x31637661), yuv420p, 4096x2304, 21049 kb/s, 23.98 fps, 24 tbr, 48 tbn, 48 tbc (default)
    Metadata:
      creation_time   : 1970-01-01T00:00:00.000000Z
      handler_name    : VideoHandler
    Stream #0:1(und): Audio: aac (LC) (mp4a / 0x6134706D), 44100 Hz, stereo, fltp, 192 kb/s (default)
    Metadata:
      creation_time   : 2012-09-21T01:14:45.000000Z
      handler_name    : IsoMedia File Produced by Google, 5-11-2011
Stream mapping:
  Stream #0:0 -> #0:0 (h264 (native) -> png (native))
Press [q] to stop, [?] for help
Output #0, image2, to 'puppies_%d.png':
  Metadata:
    major_brand     : mp42
    minor_version   : 0
    compatible_brands: isommp42
    encoder         : Lavf58.33.100
    Stream #0:0(und): Video: png, rgb24, 4096x2304, q=2-31, 200 kb/s, 0.05 fps, 0.05 tbn, 0.05 tbc (default)
    Metadata:
      creation_time   : 1970-01-01T00:00:00.000000Z
      handler_name    : VideoHandler
      encoder         : Lavc58.60.100 png
frame=    7 fps=0.2 q=-0.0 Lsize=N/A time=00:02:20.00 bitrate=N/A speed=3.68x
video:41191kB audio:0kB subtitle:0kB other streams:0kB global headers:0kB muxing overhead: unknown

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二、調整碼率和尺寸，操做耗時在77.43秒左右，文件大小從400MB左右減小到15MB左右，分辨率從4K調整爲1280*720，減輕手機等無線設備的帶寬和流量壓力。

JAMESWHALE-MB2:Downloads james$ ffmpeg -i PUPPIES_BATH_IN_4K_Original_H.264_AAC.mp4 -crf 32 -b 0.5M -minrate 0.5M -maxrate 1M -bufsize 1M -vf scale=1280:720 PUPPIES_BATH_IN_1280_720p.mp4
ffmpeg version git-2019-11-01-53c21c2 Copyright (c) 2000-2019 the FFmpeg developers
  built with Apple clang version 11.0.0 (clang-1100.0.33.8)
  configuration: --prefix=/usr/local/Cellar/ffmpeg/HEAD-53c21c2_2 --enable-shared --enable-pthreads --enable-version3 --enable-avresample --cc=clang --host-cflags='-I/Library/Java/JavaVirtualMachines/jdk1.8.0_77.jdk/Contents/Home/include -I/Library/Java/JavaVirtualMachines/jdk1.8.0_77.jdk/Contents/Home/include/darwin -fno-stack-check' --host-ldflags= --enable-ffplay --enable-gnutls --enable-gpl --enable-libaom --enable-libbluray --enable-libmp3lame --enable-libopus --enable-librubberband --enable-libsnappy --enable-libtesseract --enable-libtheora --enable-libvidstab --enable-libvorbis --enable-libvpx --enable-libx264 --enable-libx265 --enable-libxvid --enable-lzma --enable-libfontconfig --enable-libfreetype --enable-frei0r --enable-libass --enable-libopencore-amrnb --enable-libopencore-amrwb --enable-libopenjpeg --enable-librtmp --enable-libspeex --enable-libsoxr --enable-videotoolbox --disable-libjack --disable-indev=jack
  libavutil      56. 35.101 / 56. 35.101
  libavcodec     58. 60.100 / 58. 60.100
  libavformat    58. 33.100 / 58. 33.100
  libavdevice    58.  9.100 / 58.  9.100
  libavfilter     7. 66.100 /  7. 66.100
  libavresample   4.  0.  0 /  4.  0.  0
  libswscale      5.  6.100 /  5.  6.100
  libswresample   3.  6.100 /  3.  6.100
  libpostproc    55.  6.100 / 55.  6.100
Input #0, mov,mp4,m4a,3gp,3g2,mj2, from 'PUPPIES_BATH_IN_4K_Original_H.264_AAC.mp4':
  Metadata:
    major_brand     : mp42
    minor_version   : 0
    compatible_brands: isommp42
    creation_time   : 2012-09-21T01:14:45.000000Z
  Duration: 00:02:29.63, start: 0.000000, bitrate: 21244 kb/s
    Stream #0:0(und): Video: h264 (High) (avc1 / 0x31637661), yuv420p, 4096x2304, 21049 kb/s, 23.98 fps, 24 tbr, 48 tbn, 48 tbc (default)
    Metadata:
      creation_time   : 1970-01-01T00:00:00.000000Z
      handler_name    : VideoHandler
    Stream #0:1(und): Audio: aac (LC) (mp4a / 0x6134706D), 44100 Hz, stereo, fltp, 192 kb/s (default)
    Metadata:
      creation_time   : 2012-09-21T01:14:45.000000Z
      handler_name    : IsoMedia File Produced by Google, 5-11-2011
Please use -b:a or -b:v, -b is ambiguous
Stream mapping:
  Stream #0:0 -> #0:0 (h264 (native) -> h264 (libx264))
  Stream #0:1 -> #0:1 (aac (native) -> aac (native))
Press [q] to stop, [?] for help
[libx264 @ 0x7f9a43016c00] using cpu capabilities: MMX2 SSE2Fast SSSE3 SSE4.2 AVX FMA3 BMI2 AVX2
[libx264 @ 0x7f9a43016c00] profile High, level 3.1
[libx264 @ 0x7f9a43016c00] 264 - core 155 r2917 0a84d98 - H.264/MPEG-4 AVC codec - Copyleft 2003-2018 - http://www.videolan.org/x264.html - options: cabac=1 ref=3 deblock=1:0:0 analyse=0x3:0x113 me=hex subme=7 psy=1 psy_rd=1.00:0.00 mixed_ref=1 me_range=16 chroma_me=1 trellis=1 8x8dct=1 cqm=0 deadzone=21,11 fast_pskip=1 chroma_qp_offset=-2 threads=12 lookahead_threads=2 sliced_threads=0 nr=0 decimate=1 interlaced=0 bluray_compat=0 constrained_intra=0 bframes=3 b_pyramid=2 b_adapt=1 b_bias=0 direct=1 weightb=1 open_gop=0 weightp=2 keyint=250 keyint_min=24 scenecut=40 intra_refresh=0 rc_lookahead=40 rc=crf mbtree=1 crf=32.0 qcomp=0.60 qpmin=0 qpmax=69 qpstep=4 vbv_maxrate=1000 vbv_bufsize=1000 crf_max=0.0 nal_hrd=none filler=0 ip_ratio=1.40 aq=1:1.00
Output #0, mp4, to 'PUPPIES_BATH_IN_1280_720p.mp4':
  Metadata:
    major_brand     : mp42
    minor_version   : 0
    compatible_brands: isommp42
    encoder         : Lavf58.33.100
    Stream #0:0(und): Video: h264 (libx264) (avc1 / 0x31637661), yuv420p(progressive), 1280x720, q=-1--1, 500 kb/s, 24 fps, 12288 tbn, 24 tbc (default)
    Metadata:
      creation_time   : 1970-01-01T00:00:00.000000Z
      handler_name    : VideoHandler
      encoder         : Lavc58.60.100 libx264
    Side data:
      cpb: bitrate max/min/avg: 1000000/0/500000 buffer size: 1000000 vbv_delay: N/A
    Stream #0:1(und): Audio: aac (LC) (mp4a / 0x6134706D), 44100 Hz, stereo, fltp, 128 kb/s (default)
    Metadata:
      creation_time   : 2012-09-21T01:14:45.000000Z
      handler_name    : IsoMedia File Produced by Google, 5-11-2011
      encoder         : Lavc58.60.100 aac
frame= 3591 fps= 48 q=-1.0 Lsize=   14765kB time=00:02:29.60 bitrate= 808.5kbits/s dup=3 drop=0 speed=1.98x
video:12301kB audio:2351kB subtitle:0kB other streams:0kB global headers:0kB muxing overhead: 0.772543%
[libx264 @ 0x7f9a43016c00] frame I:32    Avg QP:28.63  size: 17804
[libx264 @ 0x7f9a43016c00] frame P:978   Avg QP:32.61  size:  6742
[libx264 @ 0x7f9a43016c00] frame B:2581  Avg QP:35.31  size:  2105
[libx264 @ 0x7f9a43016c00] consecutive B-frames:  3.5%  1.2%  2.0% 93.2%
[libx264 @ 0x7f9a43016c00] mb I  I16..4: 31.9% 62.0%  6.1%
[libx264 @ 0x7f9a43016c00] mb P  I16..4:  7.1%  9.9%  0.5%  P16..4: 34.3%  4.3%  1.4%  0.0%  0.0%    skip:42.6%
[libx264 @ 0x7f9a43016c00] mb B  I16..4:  0.2%  0.5%  0.0%  B16..8: 25.5%  1.6%  0.1%  direct: 0.4%  skip:71.4%  L0:39.9% L1:58.9% BI: 1.2%
[libx264 @ 0x7f9a43016c00] 8x8 transform intra:58.1% inter:91.0%
[libx264 @ 0x7f9a43016c00] coded y,uvDC,uvAC intra: 23.9% 36.4% 10.0% inter: 3.9% 5.3% 0.2%
[libx264 @ 0x7f9a43016c00] i16 v,h,dc,p: 23% 40%  8% 29%
[libx264 @ 0x7f9a43016c00] i8 v,h,dc,ddl,ddr,vr,hd,vl,hu: 17% 14% 35%  5%  6%  7%  6%  6%  5%
[libx264 @ 0x7f9a43016c00] i4 v,h,dc,ddl,ddr,vr,hd,vl,hu: 22% 20% 23%  6%  7%  7%  6%  5%  3%
[libx264 @ 0x7f9a43016c00] i8c dc,h,v,p: 70% 15% 11%  3%
[libx264 @ 0x7f9a43016c00] Weighted P-Frames: Y:4.2% UV:3.7%
[libx264 @ 0x7f9a43016c00] ref P L0: 60.8% 15.5% 18.1%  5.5%  0.1%
[libx264 @ 0x7f9a43016c00] ref B L0: 91.6%  6.5%  1.9%
[libx264 @ 0x7f9a43016c00] ref B L1: 97.6%  2.4%
[libx264 @ 0x7f9a43016c00] kb/s:673.46
[aac @ 0x7f9a43018400] Qavg: 237.150

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三、將mpeg4制式轉成webm格式，源音視頻編碼是不用寫的，ffmepg能夠本身讀取(例如，這裏的視頻編碼是h.264，音頻編碼是aac)，寫了以後反而會報Unknown decoder 'libx264'錯誤。能夠指定目標編碼，若不指定，ffmepg會根據輸出文件名後綴採用合適的音視頻編碼，例如，這裏的輸出文件名後綴是.webm, 則制式採用webm格式，視頻編碼用vp9，音頻編碼用opus。vp9還真挺厲害，在h.264基礎上，又壓縮掉了70%（400MB->107MB）。

JAMESWHALE-MB2:Downloads james$ ffmpeg -i PUPPIES_BATH_IN_4K_Original_H.264_AAC.mp4 PUPPIES_BATH_IN_4K_Original_H.264_AAC.webm
ffmpeg version git-2019-11-01-53c21c2 Copyright (c) 2000-2019 the FFmpeg developers
  built with Apple clang version 11.0.0 (clang-1100.0.33.8)
  configuration: --prefix=/usr/local/Cellar/ffmpeg/HEAD-53c21c2_2 --enable-shared --enable-pthreads --enable-version3 --enable-avresample --cc=clang --host-cflags='-I/Library/Java/JavaVirtualMachines/jdk1.8.0_77.jdk/Contents/Home/include -I/Library/Java/JavaVirtualMachines/jdk1.8.0_77.jdk/Contents/Home/include/darwin -fno-stack-check' --host-ldflags= --enable-ffplay --enable-gnutls --enable-gpl --enable-libaom --enable-libbluray --enable-libmp3lame --enable-libopus --enable-librubberband --enable-libsnappy --enable-libtesseract --enable-libtheora --enable-libvidstab --enable-libvorbis --enable-libvpx --enable-libx264 --enable-libx265 --enable-libxvid --enable-lzma --enable-libfontconfig --enable-libfreetype --enable-frei0r --enable-libass --enable-libopencore-amrnb --enable-libopencore-amrwb --enable-libopenjpeg --enable-librtmp --enable-libspeex --enable-libsoxr --enable-videotoolbox --disable-libjack --disable-indev=jack
  libavutil      56. 35.101 / 56. 35.101
  libavcodec     58. 60.100 / 58. 60.100
  libavformat    58. 33.100 / 58. 33.100
  libavdevice    58.  9.100 / 58.  9.100
  libavfilter     7. 66.100 /  7. 66.100
  libavresample   4.  0.  0 /  4.  0.  0
  libswscale      5.  6.100 /  5.  6.100
  libswresample   3.  6.100 /  3.  6.100
  libpostproc    55.  6.100 / 55.  6.100
Input #0, mov,mp4,m4a,3gp,3g2,mj2, from 'PUPPIES_BATH_IN_4K_Original_H.264_AAC.mp4':
  Metadata:
    major_brand     : mp42
    minor_version   : 0
    compatible_brands: isommp42
    creation_time   : 2012-09-21T01:14:45.000000Z
  Duration: 00:02:29.63, start: 0.000000, bitrate: 21244 kb/s
    Stream #0:0(und): Video: h264 (High) (avc1 / 0x31637661), yuv420p, 4096x2304, 21049 kb/s, 23.98 fps, 24 tbr, 48 tbn, 48 tbc (default)
    Metadata:
      creation_time   : 1970-01-01T00:00:00.000000Z
      handler_name    : VideoHandler
    Stream #0:1(und): Audio: aac (LC) (mp4a / 0x6134706D), 44100 Hz, stereo, fltp, 192 kb/s (default)
    Metadata:
      creation_time   : 2012-09-21T01:14:45.000000Z
      handler_name    : IsoMedia File Produced by Google, 5-11-2011
Stream mapping:
  Stream #0:0 -> #0:0 (h264 (native) -> vp9 (libvpx-vp9))
  Stream #0:1 -> #0:1 (aac (native) -> opus (libopus))
Press [q] to stop, [?] for help
[libvpx-vp9 @ 0x7fc0ce010600] v1.8.1
[libvpx-vp9 @ 0x7fc0ce010600] Neither bitrate nor constrained quality specified, using default CRF of 32
[libopus @ 0x7fc0ce013c00] No bit rate set. Defaulting to 96000 bps.ate=  -0.0kbits/s speed=N/A
Output #0, webm, to 'PUPPIES_BATH_IN_4K_Original_H.264_AAC.webm':
  Metadata:
    major_brand     : mp42
    minor_version   : 0
    compatible_brands: isommp42
    encoder         : Lavf58.33.100
    Stream #0:0(und): Video: vp9 (libvpx-vp9), yuv420p(progressive), 4096x2304, q=-1--1, 24 fps, 1k tbn, 24 tbc (default)
    Metadata:
      creation_time   : 1970-01-01T00:00:00.000000Z
      handler_name    : VideoHandler
      encoder         : Lavc58.60.100 libvpx-vp9
    Side data:
      cpb: bitrate max/min/avg: 0/0/0 buffer size: 0 vbv_delay: N/A
    Stream #0:1(und): Audio: opus (libopus), 48000 Hz, stereo, flt, 96 kb/s (default)
    Metadata:
      creation_time   : 2012-09-21T01:14:45.000000Z
      handler_name    : IsoMedia File Produced by Google, 5-11-2011
      encoder         : Lavc58.60.100 libopus
frame= 3588 fps=0.3 q=0.0 Lsize=  104601kB time=00:02:29.61 （這個不是耗時）bitrate=5727.3kbits/s speed=0.0116x
video:102527kB audio:1994kB subtitle:0kB other streams:0kB global headers:0kB muxing overhead: 0.076851%
複製代碼

四、將mpeg4制式轉成webm制式，源音視頻編碼仍然從輸入文件獲取，此次明確指定目標視頻編碼爲vp8，目標音頻編碼沒有明確指定，ffmpeg根據輸出文件後綴.webm默認採用opus音頻編碼。vp8在h.264基礎上，又壓縮掉了20%左右（15.1MB->12.1MB）,操做耗時在599.15秒左右。

JAMESWHALE-MB2:Downloads james$ ffmpeg -i PUPPIES_BATH_IN_1280_720p.mp4  -vcodec vp8 -crf 32 -b 0.5M -minrate 0.5M -maxrate 1M -bufsize 1M PUPPIES_BATH_IN_1280_720p.webm
ffmpeg version git-2019-11-01-53c21c2 Copyright (c) 2000-2019 the FFmpeg developers
  built with Apple clang version 11.0.0 (clang-1100.0.33.8)
  configuration: --prefix=/usr/local/Cellar/ffmpeg/HEAD-53c21c2_2 --enable-shared --enable-pthreads --enable-version3 --enable-avresample --cc=clang --host-cflags='-I/Library/Java/JavaVirtualMachines/jdk1.8.0_77.jdk/Contents/Home/include -I/Library/Java/JavaVirtualMachines/jdk1.8.0_77.jdk/Contents/Home/include/darwin -fno-stack-check' --host-ldflags= --enable-ffplay --enable-gnutls --enable-gpl --enable-libaom --enable-libbluray --enable-libmp3lame --enable-libopus --enable-librubberband --enable-libsnappy --enable-libtesseract --enable-libtheora --enable-libvidstab --enable-libvorbis --enable-libvpx --enable-libx264 --enable-libx265 --enable-libxvid --enable-lzma --enable-libfontconfig --enable-libfreetype --enable-frei0r --enable-libass --enable-libopencore-amrnb --enable-libopencore-amrwb --enable-libopenjpeg --enable-librtmp --enable-libspeex --enable-libsoxr --enable-videotoolbox --disable-libjack --disable-indev=jack
  libavutil      56. 35.101 / 56. 35.101
  libavcodec     58. 60.100 / 58. 60.100
  libavformat    58. 33.100 / 58. 33.100
  libavdevice    58.  9.100 / 58.  9.100
  libavfilter     7. 66.100 /  7. 66.100
  libavresample   4.  0.  0 /  4.  0.  0
  libswscale      5.  6.100 /  5.  6.100
  libswresample   3.  6.100 /  3.  6.100
  libpostproc    55.  6.100 / 55.  6.100
Input #0, mov,mp4,m4a,3gp,3g2,mj2, from 'PUPPIES_BATH_IN_1280_720p.mp4':
  Metadata:
    major_brand     : isom
    minor_version   : 512
    compatible_brands: isomiso2avc1mp41
    encoder         : Lavf58.33.100
  Duration: 00:02:29.63, start: 0.000000, bitrate: 808 kb/s
    Stream #0:0(und): Video: h264 (High) (avc1 / 0x31637661), yuv420p, 1280x720, 673 kb/s, 24 fps, 24 tbr, 12288 tbn, 48 tbc (default)
    Metadata:
      handler_name    : VideoHandler
    Stream #0:1(und): Audio: aac (LC) (mp4a / 0x6134706D), 44100 Hz, stereo, fltp, 128 kb/s (default)
    Metadata:
      handler_name    : IsoMedia File Produced by Google, 5-11-2011
Please use -b:a or -b:v, -b is ambiguous
Stream mapping:
  Stream #0:0 -> #0:0 (h264 (native) -> vp8 (libvpx))
  Stream #0:1 -> #0:1 (aac (native) -> opus (libopus))
Press [q] to stop, [?] for help
[libopus @ 0x7fa68c002800] No bit rate set. Defaulting to 96000 bps.
[libvpx @ 0x7fa68c001600] v1.8.1
Output #0, webm, to 'PUPPIES_BATH_IN_1280_720p.webm':
  Metadata:
    major_brand     : isom
    minor_version   : 512
    compatible_brands: isomiso2avc1mp41
    encoder         : Lavf58.33.100
    Stream #0:0(und): Video: vp8 (libvpx), yuv420p, 1280x720, q=-1--1, 500 kb/s, 24 fps, 1k tbn, 24 tbc (default)
    Metadata:
      handler_name    : VideoHandler
      encoder         : Lavc58.60.100 libvpx
    Side data:
      cpb: bitrate max/min/avg: 0/0/0 buffer size: 1000000 vbv_delay: N/A
    Stream #0:1(und): Audio: opus (libopus), 48000 Hz, stereo, flt, 96 kb/s (default)
    Metadata:
      handler_name    : IsoMedia File Produced by Google, 5-11-2011
      encoder         : Lavc58.60.100 libopus
frame= 3591 fps=6.0 q=0.0 Lsize=   11812kB time=00:02:29.61 bitrate= 646.7kbits/s speed=0.249x
video:9750kB audio:1984kB subtitle:0kB other streams:0kB global headers:0kB muxing overhead: 0.665825%
複製代碼

總結

遇到問題不能怕，即便通過了不少天的折磨，仍然須要保持耐心和清醒的頭腦，問題解決以後的成就感是對過程當中付出的最大回報。

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