FFmpeg中OS X设备操作
在FFmpeg中采集OS X系统的输入输出设备，常规方式采用的是OS X的avfoundation设备进行采集。
ffmpeg -h demuxer=avfoundation
Demuxer avfoundation [AVFoundation input device]:
AVFoundation input device AVOptions:
-list_devices <int> .D....... list available devices (from 0 to 1) (default false)
true .D.......
false .D.......
-video_device_index <int> .D....... select video device by index for devices with same name (starts at 0) (from -1 to INT_MAX) (default -1)
-audio_device_index <int> .D....... select audio device by index for devices with same name (starts at 0) (from -1 to INT_MAX) (default -1)
-pixel_format <pix_fmt> .D....... set pixel format (default yuv420p)
-framerate <video_rate> .D....... set frame rate (default "ntsc")
-video_size <image_size> .D....... set video size
-capture_cursor <int> .D....... capture the screen cursor (from 0 to 1) (default 0)
-capture_mouse_clicks <int> .D....... capture the screen mouse clicks (from 0 to 1) (default 0)
1、OS X下查看设备列表
ffmpeg -devices
Devices:
D. = Demuxing supported
.E = Muxing supported
--
D avfoundation AVFoundation input device
D lavfi Libavfilter virtual input device
E sdl,sdl2 SDL2 output device
如上信息，分为两大部分：
- 解封装或封装的支持情况
- 设备列表
2、OS X下设备采集
枚举avfoundation支持的输入设备：
ffmpeg -f avfoundation -list_devices true -i ""
[AVFoundation input device @ 0x7fea535022c0] AVFoundation video devices:
[AVFoundation input device @ 0x7fea535022c0] [0] FaceTime 高清摄像头（内建）
[AVFoundation input device @ 0x7fea535022c0] [1] Capture screen 0
[AVFoundation input device @ 0x7fea535022c0] AVFoundation audio devices:
[AVFoundation input device @ 0x7fea535022c0] [0] Built-in Microphone
视频输入设备：
- [0] FaceTime 高清摄像头（内建）
- [1] Capture screen 0
音频输入设备： - [0] Built-in Microphone
avfoundation除了枚举了物理摄像头（FaceTime 高清摄像头）之外，还包括了1个虚拟设备，即Capture screen 0设备代表了OS X桌面。
（1）采集内置摄像头
ffmpeg -f avfoundation -i "FaceTime 高清摄像头（内建）" out.mp4
Input #0, avfoundation, from 'FaceTime 高清摄像头（内建）':
Duration: N/A, start: 33714.868500, bitrate: N/A
Stream #0:0: Video: rawvideo (UYVY / 0x59565955), uyvy422, 1280x720, 12 tbr, 1000k tbn, 1000k tbc
Stream mapping:
Stream #0:0 -> #0:0 (rawvideo (native) -> h264 (libx264))
Press [q] to stop, [?] for help
[libx264 @ 0x7fb10b87c600] using cpu capabilities: MMX2 SSE2Fast SSSE3 SSE4.2 AVX
[libx264 @ 0x7fb10b87c600] profile High 4:2:2, level 3.1, 4:2:2 8-bit
[libx264 @ 0x7fb10b87c600] 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=6 lookahead_threads=1 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=12 scenecut=40 intra_refresh=0 rc_lookahead=40 rc=crf mbtree=1 crf=23.0 qcomp=0.60 qpmin=0 qpmax=69 qpstep=4 ip_ratio=1.40 aq=1:1.00
Output #0, mp4, to 'out.mp4':
Metadata:
encoder : Lavf58.20.100
Stream #0:0: Video: h264 (libx264) (avc1 / 0x31637661), yuv422p, 1280x720, q=-1--1, 12 fps, 12288 tbn, 12 tbc
Metadata:
encoder : Lavc58.35.100 libx264
Side data:
cpb: bitrate max/min/avg: 0/0/0 buffer size: 0 vbv_delay: -1
frame= 11 fps=0.0 q=0.0 size= 0kB time=00:00:00.00 bitrate=N/A speed=
frame= 18 fps= 16 q=0.0 size= 0kB time=00:00:00.00 bitrate=N/A speed=
frame= 24 fps= 14 q=0.0 size= 0kB time=00:00:00.00 bitrate=N/A speed=
frame= 31 fps= 14 q=0.0 size= 0kB time=00:00:00.00 bitrate=N/A speed=
frame= 37 fps= 13 q=0.0 size= 0kB time=00:00:00.00 bitrate=N/A speed=
frame= 44 fps= 13 q=0.0 size= 0kB time=00:00:00.00 bitrate=N/A speed=
frame= 51 fps= 13 q=26.0 size= 0kB time=-00:00:00.16 bitrate=N/A speed=N
frame= 58 fps= 13 q=26.0 size= 0kB time=00:00:00.41 bitrate= 0.9kbits/
frame= 65 fps= 13 q=26.0 size= 0kB time=00:00:01.00 bitrate= 0.4kbits/
frame= 71 fps= 13 q=26.0 size= 0kB time=00:00:01.50 bitrate= 0.3kbits/frame
frame= 78 fps= 13 q=26.0 size= 0kB time=00:00:02.08 bitrate= 0.2kbits/
frame= 84 fps= 13 q=26.0 size= 256kB time=00:00:02.58 bitrate= 811.9kbits/
frame= 90 fps= 13 q=26.0 size= 256kB time=00:00:03.08 bitrate= 680.3kbits/
frame= 97 fps= 13 q=26.0 size= 512kB time=00:00:03.66 bitrate=1144.0kbits/
frame= 103 fps= 12 q=26.0 size= 512kB time=00:00:04.16 bitrate=1006.7kbits/
frame= 110 fps= 12 q=26.0 size= 768kB time=00:00:04.75 bitrate=1324.6kbits/
frame= 113 fps=9.6 q=-1.0 Lsize= 1950kB time=00:00:09.16 bitrate=1742.6kbits/s speed=0.778x
video:1948kB audio:0kB subtitle:0kB other streams:0kB global headers:0kB muxing overhead: 0.110501%
（2）采集OS X桌面
ffmpeg -f avfoundation -i "Capture screen 0" -r:v 30 out1.mp4
Input #0, avfoundation, from 'Capture screen 0':
Duration: N/A, start: 34246.268167, bitrate: N/A
Stream #0:0: Video: rawvideo (UYVY / 0x59565955), uyvy422, 2560x1600, 1000k tbr, 1000k tbn, 1000k tbc
Stream mapping:
Stream #0:0 -> #0:0 (rawvideo (native) -> h264 (libx264))
Press [q] to stop, [?] for help
[libx264 @ 0x7fea3f2b7400] using cpu capabilities: MMX2 SSE2Fast SSSE3 SSE4.2 AVX
[libx264 @ 0x7fea3f2b7400] profile High 4:2:2, level 5.0, 4:2:2 8-bit
[libx264 @ 0x7fea3f2b7400] 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=6 lookahead_threads=1 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=25 scenecut=40 intra_refresh=0 rc_lookahead=40 rc=crf mbtree=1 crf=23.0 qcomp=0.60 qpmin=0 qpmax=69 qpstep=4 ip_ratio=1.40 aq=1:1.00
Output #0, mp4, to 'out1.mp4':
Metadata:
encoder : Lavf58.20.100
Stream #0:0: Video: h264 (libx264) (avc1 / 0x31637661), yuv422p, 2560x1600, q=-1--1, 30 fps, 15360 tbn, 30 tbc
Metadata:
encoder : Lavc58.35.100 libx264
Side data:
cpb: bitrate max/min/avg: 0/0/0 buffer size: 0 vbv_delay: -1
frame= 17 fps=0.0 q=0.0 size= 0kB time=00:00:00.00 bitrate=N/A speed= 0
frame= 33 fps= 32 q=0.0 size= 0kB time=00:00:00.00 bitrate=N/A speed= 0
frame= 55 fps= 30 q=29.0 size= 256kB time=00:00:00.06 bitrate=31432.2kbits/
frame= 81 fps= 30 q=29.0 size= 256kB time=00:00:00.93 bitrate=2247.2kbits/s
frame= 98 fps= 30 q=29.0 size= 256kB time=00:00:01.50 bitrate=1398.3kbits/s
frame= 114 fps= 30 q=29.0 size= 256kB time=00:00:02.03 bitrate=1031.5kbits/s
frame= 130 fps= 30 q=29.0 size= 256kB time=00:00:02.56 bitrate= 817.2kbits/s
frame= 148 fps= 30 q=29.0 size= 256kB time=00:00:03.16 bitrate= 662.4kbits/s
frame= 148 fps= 21 q=-1.0 Lsize= 422kB time=00:00:04.83 bitrate= 714.5kbits/
s dup=95 drop=0 speed=0.691x
video:419kB audio:0kB subtitle:0kB other streams:0kB global headers:0kB muxing overhead: 0.606895%
参数Capture screen 0指定了桌面0为输入设备，与x11grab的方式类似，我们还可以录制鼠标，在OS X上通过capture_cursor来指定：
ffmpeg -f avfoundation -capture_cursor 1 -i "Capture screen 0" -r:v 30 out2.mp4
（3）采集麦克风
ffmpeg -f avfoundation -i "0:0" out.aac
通过参数“0:0”分别指定第0个视频设备与第0个音频设备，输出信息如下：
Input #0, avfoundation, from '0:0':
Duration: N/A, start: 35022.728322, bitrate: N/A
Stream #0:0: Video: rawvideo (UYVY / 0x59565955), uyvy422, 1280x720, 23.92 tbr, 1000k tbn, 1000k tbc
Stream #0:1: Audio: pcm_f32le, 44100 Hz, stereo, flt, 2822 kb/s
Stream mapping:
Stream #0:1 -> #0:0 (pcm_f32le (native) -> aac (native))
Press [q] to stop, [?] for help
Output #0, adts, to 'out.aac':
Metadata:
encoder : Lavf58.20.100
Stream #0:0: Audio: aac (LC), 44100 Hz, stereo, fltp, 128 kb/s
Metadata:
encoder : Lavc58.35.100 aac
size= 71kB time=00:00:04.50 bitrate= 129.6kbits/s speed=1.05x
video:0kB audio:70kB subtitle:0kB other streams:0kB global headers:0kB muxing overhead: 1.896118%
如上信息所示，采集的数据包含了视频rawvideo数据和音频pcm_f32le数据，但是编码输出只有AAC的编码的数据。
除了以上方法，还可以使用设备索引参数指定设备采集：
ffmpeg -f avfoundation -video_deivce_index 0 -i ":0" out.aac
ffmpeg -f avfoundation -video_deivce_index 0 -audio_device_index 0 out.aac
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