help语法

贴出（后来重新安装的支持了ass等库的）ffmpeg的help帮助信息：

  1. ➜  ~ ffmpeg --help
  2. ffmpeg version 4.0.2 Copyright (c) 2000-2018 the FFmpeg developers
  3.   built with Apple LLVM version 10.0.0 (clang-1000.11.45.2)
  4.   configuration: --prefix=/usr/local/Cellar/ffmpeg/4.0.2 --enable-shared --enable-pthreads --enable-version3 --enable-hardcoded-tables --enable-avresample --cc=clang --host-cflags= --host-ldflags= --enable-gpl --enable-libass --enable-libfdk-aac --enable-libfontconfig --enable-libfreetype --enable-libmp3lame --enable-libopus --enable-libvorbis --enable-libvpx --enable-libx264 --enable-libx265 --enable-libxvid --enable-opencl --enable-videotoolbox --disable-lzma --enable-nonfree
  5.   libavutil      56. 14.100 / 56. 14.100
  6.   libavcodec     58. 18.100 / 58. 18.100
  7.   libavformat    58. 12.100 / 58. 12.100
  8.   libavdevice    58.  3.100 / 58.  3.100
  9.   libavfilter     7. 16.100 /  7. 16.100
  10.   libavresample   4.  0.  0 /  4.  0.  0
  11.   libswscale      5.  1.100 /  5.  1.100
  12.   libswresample   3.  1.100 /  3.  1.100
  13.   libpostproc    55.  1.100 / 55.  1.100
  14. Hyper fast Audio and Video encoder
  15. usage: ffmpeg [options] [[infile options] -i infile]... {[outfile options] outfile}...
  17. Getting help:
  18.     -h      -- print basic options
  19.     -h long -- print more options
  20.     -h full -- print all options (including all format and codec specific options, very long)
  21.     -h type=name -- print all options for the named decoder/encoder/demuxer/muxer/filter/bsf
  22.     See man ffmpeg for detailed description of the options.
  24. Print help / information / capabilities:
  25. -L                  show license
  26. -h topic            show help
  27. -? topic            show help
  28. -help topic         show help
  29. --help topic        show help
  30. -version            show version
  31. -buildconf          show build configuration
  32. -formats            show available formats
  33. -muxers             show available muxers
  34. -demuxers           show available demuxers
  35. -devices            show available devices
  36. -codecs             show available codecs
  37. -decoders           show available decoders
  38. -encoders           show available encoders
  39. -bsfs               show available bit stream filters
  40. -protocols          show available protocols
  41. -filters            show available filters
  42. -pix_fmts           show available pixel formats
  43. -layouts            show standard channel layouts
  44. -sample_fmts        show available audio sample formats
  45. -colors             show available color names
  46. -sources device     list sources of the input device
  47. -sinks device       list sinks of the output device
  48. -hwaccels           show available HW acceleration methods
  50. Global options (affect whole program instead of just one file:
  51. -loglevel loglevel  set logging level
  52. -v loglevel         set logging level
  53. -report             generate a report
  54. -max_alloc bytes    set maximum size of a single allocated block
  55. -y                  overwrite output files
  56. -n                  never overwrite output files
  57. -ignore_unknown     Ignore unknown stream types
  58. -filter_threads     number of non-complex filter threads
  59. -filter_complex_threads  number of threads for -filter_complex
  60. -stats              print progress report during encoding
  61. -max_error_rate maximum error rate  ratio of errors (0.0: no errors, 1.0: 100% errors) above which ffmpeg returns an error instead of success.
  62. -bits_per_raw_sample number  set the number of bits per raw sample
  63. -vol volume         change audio volume (256=normal)
  65. Per-file main options:
  66. -f fmt              force format
  67. -c codec            codec name
  68. -codec codec        codec name
  69. -pre preset         preset name
  70. -map_metadata outfile[,metadata]:infile[,metadata]  set metadata information of outfile from infile
  71. -t duration         record or transcode "duration" seconds of audio/video
  72. -to time_stop       record or transcode stop time
  73. -fs limit_size      set the limit file size in bytes
  74. -ss time_off        set the start time offset
  75. -sseof time_off     set the start time offset relative to EOF
  76. -seek_timestamp     enable/disable seeking by timestamp with -ss
  77. -timestamp time     set the recording timestamp ('now' to set the current time)
  78. -metadata string=string  add metadata
  79. -program title=string:st=number...  add program with specified streams
  80. -target type        specify target file type ("vcd", "svcd", "dvd", "dv" or "dv50" with optional prefixes "pal-", "ntsc-" or "film-")
  81. -apad               audio pad
  82. -frames number      set the number of frames to output
  83. -filter filter_graph  set stream filtergraph
  84. -filter_script filename  read stream filtergraph description from a file
  85. -reinit_filter      reinit filtergraph on input parameter changes
  86. -discard            discard
  87. -disposition        disposition
  89. Video options:
  90. -vframes number     set the number of video frames to output
  91. -r rate             set frame rate (Hz value, fraction or abbreviation)
  92. -s size             set frame size (WxH or abbreviation)
  93. -aspect aspect      set aspect ratio (4:3, 16:9 or 1.3333, 1.7777)
  94. -bits_per_raw_sample number  set the number of bits per raw sample
  95. -vn                 disable video
  96. -vcodec codec       force video codec ('copy' to copy stream)
  97. -timecode hh:mm:ss[:;.]ff  set initial TimeCode value.
  98. -pass n             select the pass number (1 to 3)
  99. -vf filter_graph    set video filters
  100. -ab bitrate         audio bitrate (please use -b:a)
  101. -b bitrate          video bitrate (please use -b:v)
  102. -dn                 disable data
  104. Audio options:
  105. -aframes number     set the number of audio frames to output
  106. -aq quality         set audio quality (codec-specific)
  107. -ar rate            set audio sampling rate (in Hz)
  108. -ac channels        set number of audio channels
  109. -an                 disable audio
  110. -acodec codec       force audio codec ('copy' to copy stream)
  111. -vol volume         change audio volume (256=normal)
  112. -af filter_graph    set audio filters
  114. Subtitle options:
  115. -s size             set frame size (WxH or abbreviation)
  116. -sn                 disable subtitle
  117. -scodec codec       force subtitle codec ('copy' to copy stream)
  118. -stag fourcc/tag    force subtitle tag/fourcc
  119. -fix_sub_duration   fix subtitles duration
  120. -canvas_size size   set canvas size (WxH or abbreviation)
  121. -spre preset        set the subtitle options to the indicated preset

供参考。