采集步骤如下

1. 下载安装ffmpeg

下载地址：https://www.ffmpeg.org/download.html#build-mac

或者通过mac命令安装（略）

2. 查看采集MAC视频音频设备

ffmpeg -hide_banner -devices

执行结果（看得懂的看，看不懂的略，不影响后续）

Devices:
 D. = Demuxing supported
 .E = Muxing supported
 --
 D  avfoundation    AVFoundation input device
 D  lavfi           Libavfilter virtual input device
  E sdl,sdl2        SDL2 output device

3. 列出设备清单

ffmpeg -hide_banner -f avfoundation -list_devices true -i " "

执行结果

[AVFoundation input device @ 0x7f8780c2d080] AVFoundation video devices:
[AVFoundation input device @ 0x7f8780c2d080] [0] FaceTime高清摄像头（内建）
[AVFoundation input device @ 0x7f8780c2d080] [1] Capture screen 0
[AVFoundation input device @ 0x7f8780c2d080] AVFoundation audio devices:
[AVFoundation input device @ 0x7f8780c2d080] [0] 外置麦克风
[AVFoundation input device @ 0x7f8780c2d080] [1] MacBook Pro麦克风

解释

识别并列出两种类型设备，视频（video）设备和音频（audio）设备，注意编号（这样[0]，[1]）；视频的有两个设备，编号为0的是屏幕上方的摄像头，编号为1的是桌面；音频也有两个设备，一个是外置麦克风（我插这耳机），另外一个是MAC自带内置的麦克风，如果拔掉耳机，那么编号为0的将仅仅是内置麦克风。

值得注意的是，有人可能安装了录屏软件，这些录屏软件安装时可能会安装上一些其它虚拟设备，注意区分。

4. 查看视频采集分辨率

ffmpeg -hide_banner -f avfoundation -i 0

解释

-hide_banner 隐藏ffmpeg编译信息输出，-f 表示格式，后面的avfoundation表示av设备， -i 表示输入（采集来源），后面的0表示视频设备编号（通过查阅ffmpeg的api也可以使用设备名称）

输出结果：（非常多，这里列出部分）

[avfoundation @ 0x7fca5b808200] Selected framerate (29.970030) is not supported by the device.
[avfoundation @ 0x7fca5b808200] Supported modes:
[avfoundation @ 0x7fca5b808200]   640x480@[30.000030 30.000030]fps
[avfoundation @ 0x7fca5b808200]   640x480@[29.000049 29.000049]fps
[avfoundation @ 0x7fca5b808200]   640x480@[28.000067 28.000067]fps
...
[avfoundation @ 0x7fca5b808200]   640x480@[5.000000 5.000000]fps
[avfoundation @ 0x7fca5b808200]   640x480@[4.000000 4.000000]fps
[avfoundation @ 0x7fca5b808200]   640x480@[3.000000 3.000000]fps
[avfoundation @ 0x7fca5b808200]   640x480@[2.000000 2.000000]fps
[avfoundation @ 0x7fca5b808200]   640x480@[1.000000 1.000000]fps
...
[avfoundation @ 0x7fca5b808200]   1280x720@[6.000002 6.000002]fps
[avfoundation @ 0x7fca5b808200]   1280x720@[5.000000 5.000000]fps
[avfoundation @ 0x7fca5b808200]   1280x720@[4.000000 4.000000]fps
[avfoundation @ 0x7fca5b808200]   1280x720@[3.000000 3.000000]fps
[avfoundation @ 0x7fca5b808200]   1280x720@[2.000000 2.000000]fps
[avfoundation @ 0x7fca5b808200]   1280x720@[1.000000 1.000000]fps

5. 采集命令

采集为Mp4格式：

ffmpeg -hide_banner -f avfoundation -video_size 1280x720 -framerate 30 -i "0:0" -pix_fmt yuv420p -c:v libx264 -vf "scale=640:-1" -strict -2 out.mp4

解释

-video_size 1280x720，采集尺寸，注意这个是来设备源提供的支持的尺寸，不可以随意写，否则会提示设备不支持该尺寸。

-framerate 帧率，需要和上面的video_size 对应的值在设备清单里面能找到

-i 输入设备，注意了，如果仅配置为0也可，这样会采集不到声音，格式含义是 <视频设备ID>:<音频设备ID>，再次提醒，设备ID不一定是0，需要通过之前的命令预先查查（如果是可拔插设备，如摄像头，麦克风之类的，拔插后的设备序号可能发生变化，注意甄别）

-pix_fmt转换成目标后的像素格式，ffmpeg支持好几种，需要注意的是使用yuv420p可能会支持绝大多数设备，比如MacOS使用此配置就可以直接预览采集到的媒体了。

-c:v 转换后的视频部分编码（c表示codec，v表示video），这里采用libx264

-vf 转换后的视频尺寸，scale=640:-1，表示输出宽为640，高度自动匹配。注意，当自动算出来的数值不支持时（可能是奇数），需要我们手动修改为最接近的偶数值。如果想输出媒体尺寸和源媒体一致，可删除此配置选项

后面的自己查资料了

采集为m3u8格式：

ffmpeg -hide_banner -f avfoundation -video_size 1280x720 -framerate 30 -i "0:0" -pix_fmt yuv420p -c:v libx264 -hls_list_size 0 -hls_wrap 0 -strict -2 -vbsf h264_mp4toannexb -absf aac_adtstoasc -f hls index.m3u8

或

ffmpeg -hide_banner -f avfoundation -video_size 1280x720 -framerate 30 -i "0:0" -pix_fmt yuv420p -c:v libx264 -hls_enc true -hls_enc_key 21232f297a57a5a743894a0e4a801fc3 -hls_enc_key_url key.key -hls_list_size 0 -hls_wrap 0 -strict -2 -vbsf h264_mp4toannexb -absf aac_adtstoasc -f hls index-%06d.m3u8

两者都能采集到m3u8和ts文件，只是后者会对ts加密，加密算法和秘钥会保存在m3u8和key文件中，这里不做具体解释，给出部分有用的hls参数供参考，如下：

hls muxer AVOptions:
  -start_number      <int64>      E........ set first number in the sequence (from 0 to I64_MAX) (default 0)
  -hls_time          <float>      E........ set segment length in seconds (from 0 to FLT_MAX) (default 2)
  -hls_init_time     <float>      E........ set segment length in seconds at init list (from 0 to FLT_MAX) (default 0)
  -hls_list_size     <int>        E........ set maximum number of playlist entries (from 0 to INT_MAX) (default 5)
  -hls_delete_threshold <int>        E........ set number of unreferenced segments to keep before deleting (from 1 to INT_MAX) (default 1)
  -hls_ts_options    <string>     E........ set hls mpegts list of options for the container format used for hls
  -hls_vtt_options   <string>     E........ set hls vtt list of options for the container format used for hls
  -hls_wrap          <int>        E........ set number after which the index wraps (will be deprecated) (from 0 to INT_MAX) (default 0)
  -hls_allow_cache   <int>        E........ explicitly set whether the client MAY (1) or MUST NOT (0) cache media segments (from INT_MIN to INT_MAX) (default -1)
  -hls_base_url      <string>     E........ url to prepend to each playlist entry
  -hls_segment_filename <string>     E........ filename template for segment files
  -hls_segment_size  <int>        E........ maximum size per segment file, (in bytes) (from 0 to INT_MAX) (default 0)
  -hls_key_info_file <string>     E........ file with key URI and key file path
  -hls_enc           <boolean>    E........ enable AES128 encryption support (default false)
  -hls_enc_key       <string>     E........ hex-coded 16 byte key to encrypt the segments
  -hls_enc_key_url   <string>     E........ url to access the key to decrypt the segments
  -hls_enc_iv        <string>     E........ hex-coded 16 byte initialization vector
  -hls_subtitle_path <string>     E........ set path of hls subtitles
  -hls_segment_type  <int>        E........ set hls segment files type (from 0 to 1) (default mpegts)
     mpegts                       E........ make segment file to mpegts files in m3u8
     fmp4                         E........ make segment file to fragment mp4 files in m3u8
  -hls_fmp4_init_filename <string>     E........ set fragment mp4 file init filename (default "init.mp4")
  -hls_flags         <flags>      E........ set flags affecting HLS playlist and media file generation (default 0)
     single_file                  E........ generate a single media file indexed with byte ranges
     temp_file                    E........ write segment and playlist to temporary file and rename when complete
     delete_segments              E........ delete segment files that are no longer part of the playlist
     round_durations              E........ round durations in m3u8 to whole numbers
     discont_start                E........ start the playlist with a discontinuity tag
     omit_endlist                 E........ Do not append an endlist when ending stream
     split_by_time                E........ split the hls segment by time which user set by hls_time
     append_list                  E........ append the new segments into old hls segment list
     program_date_time              E........ add EXT-X-PROGRAM-DATE-TIME
     second_level_segment_index              E........ include segment index in segment filenames when use_localtime
     second_level_segment_duration              E........ include segment duration in segment filenames when use_localtime
     second_level_segment_size              E........ include segment size in segment filenames when use_localtime
     periodic_rekey               E........ reload keyinfo file periodically for re-keying
     independent_segments              E........ add EXT-X-INDEPENDENT-SEGMENTS, whenever applicable
     iframes_only                 E........ add EXT-X-I-FRAMES-ONLY, whenever applicable
  -use_localtime     <boolean>    E........ set filename expansion with strftime at segment creation(will be deprecated ) (default false)
  -strftime          <boolean>    E........ set filename expansion with strftime at segment creation (default false)
  -use_localtime_mkdir <boolean>    E........ create last directory component in strftime-generated filename(will be deprecated) (default false)
  -strftime_mkdir    <boolean>    E........ create last directory component in strftime-generated filename (default false)
  -hls_playlist_type <int>        E........ set the HLS playlist type (from 0 to 2) (default 0)
     event                        E........ EVENT playlist
     vod                          E........ VOD playlist
  -method            <string>     E........ set the HTTP method(default: PUT)
  -hls_start_number_source <int>        E........ set source of first number in sequence (from 0 to 2) (default generic)
     generic                      E........ start_number value (default)
     epoch                        E........ seconds since epoch
     datetime                     E........ current datetime as YYYYMMDDhhmmss
  -http_user_agent   <string>     E........ override User-Agent field in HTTP header
  -var_stream_map    <string>     E........ Variant stream map string
  -cc_stream_map     <string>     E........ Closed captions stream map string
  -master_pl_name    <string>     E........ Create HLS master playlist with this name
  -master_pl_publish_rate <int>        E........ Publish master play list every after this many segment intervals (from 0 to UINT32_MAX) (default 0)
  -http_persistent   <boolean>    E........ Use persistent HTTP connections (default false)
  -timeout           <duration>   E........ set timeout for socket I/O operations (default -0.000001)
  -ignore_io_errors  <boolean>    E........ Ignore IO errors for stable long-duration runs with network output (default false)
  -headers           <string>     E........ set custom HTTP headers, can override built in default headers

就这样了，好运