FFmpeg的3.3.4 avfoundation使用命令行

Question

只记录在MacOS塞拉利昂画面的特定部分我使用的FFmpeg版本3.3.4（通过BREW安装）通过命令行中的一些自动化测试来记录我的桌面在我的macOS Sierra（10.12.6）上。

我想记录只在屏幕的特定部分，但不幸的是，我不能找到文档中的正确的选项，以达到我的目标。

按照FFmpeg documentation for avfoundation，这是我用命令：

ffmpeg 
-f avfoundation // avfoundation 
-pix_fmt uyvy422 // pixel format 
-i 1    // input: desktop 
-r 30    // framerate for output 
[PATH]/test.mp4  // filename 

当我运行这个命令，我有以下的输出：

ffmpeg version 3.3.4 Copyright (c) 2000-2017 the FFmpeg developers 
    built with Apple LLVM version 9.0.0 (clang-900.0.37) 
    configuration: --prefix=/usr/local/Cellar/ffmpeg/3.3.4 --enable-shared --enable-pthreads --enable-version3 --enable-hardcoded-tables --enable-avresample --cc=clang --host-cflags= --host-ldflags= --enable-gpl --enable-ffplay --enable-frei0r --enable-libass --enable-libfdk-aac --enable-libfreetype --enable-libmp3lame --enable-libopencore-amrnb --enable-libopencore-amrwb --enable-libopus --enable-librtmp --enable-libschroedinger --enable-libspeex --enable-libtheora --enable-libvorbis --enable-libvpx --enable-libx264 --enable-libx265 --enable-libxvid --enable-opencl --enable-videotoolbox --enable-openssl --disable-lzma --enable-libopenjpeg --disable-decoder=jpeg2000 --extra-cflags=-I/usr/local/Cellar/openjpeg/2.3.0/include/openjpeg-2.3 --enable-nonfree --enable-vda 
    libavutil  55. 58.100/55. 58.100 
    libavcodec  57. 89.100/57. 89.100 
    libavformat 57. 71.100/57. 71.100 
    libavdevice 57. 6.100/57. 6.100 
    libavfilter  6. 82.100/6. 82.100 
    libavresample 3. 5. 0/3. 5. 0 
    libswscale  4. 6.100/4. 6.100 
    libswresample 2. 7.100/2. 7.100 
    libpostproc 54. 5.100/54. 5.100 
[avfoundation @ 0x7fb7d4005800] Stream #0: not enough frames to estimate rate; consider increasing probesize 
Input #0, avfoundation, from '1': 
    Duration: N/A, start: 7263.782833, bitrate: N/A 
    Stream #0:0: Video: rawvideo (UYVY/0x59565955), uyvy422, 1920x1080, 1000k tbr, 1000k tbn, 1000k tbc 
Stream mapping: 
    Stream #0:0 -> #0:0 (rawvideo (native) -> h264 (libx264)) 
Press [q] to stop, [?] for help 
No pixel format specified, yuv422p for H.264 encoding chosen. 
Use -pix_fmt yuv420p for compatibility with outdated media players. 
[libx264 @ 0x7fb7d4028400] using cpu capabilities: MMX2 SSE2Fast SSSE3 SSE4.2 AVX FMA3 AVX2 LZCNT BMI2 
[libx264 @ 0x7fb7d4028400] profile High 4:2:2, level 4.0, 4:2:2 8-bit 
[libx264 @ 0x7fb7d4028400] 264 - core 148 r2795 aaa9aa8 - H.264/MPEG-4 AVC codec - Copyleft 2003-2017 - 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 '[PATH]/test.mp4': 
    Metadata: 
    encoder   : Lavf57.71.100 
    Stream #0:0: Video: h264 (libx264) ([33][0][0][0]/0x0021), yuv422p, 1920x1080, q=-1--1, 30 fps, 15360 tbn, 30 tbc 
    Metadata: 
     encoder   : Lavc57.89.100 libx264 
    Side data: 
     cpb: bitrate max/min/avg: 0/0/0 buffer size: 0 vbv_delay: -1 
frame= 83 fps= 28 q=-1.0 Lsize=  525kB time=00:00:02.66 bitrate=1612.6kbits/s dup=1 drop=0 speed=0.889x 

我试图用-video_size选项设置视频帧的大小，但它不起作用。

Answer 1

首先，你需要找到对应于您的屏幕AVFoundation设备的名称：

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

[AVFoundation input device @ 0x7fc1cd40ec60] AVFoundation video devices: 
[AVFoundation input device @ 0x7fc1cd40ec60] [0] HD Pro Webcam C920 
[AVFoundation input device @ 0x7fc1cd40ec60] [1] FaceTime HD Camera (Built-in) 
[AVFoundation input device @ 0x7fc1cd40ec60] [2] Capture screen 0 
[AVFoundation input device @ 0x7fc1cd40ec60] AVFoundation audio devices: 
[AVFoundation input device @ 0x7fc1cd40ec60] [0] HD Pro Webcam C920 
[AVFoundation input device @ 0x7fc1cd40ec60] [1] Built-in Microphone 

所以我的屏幕是设备[2]因为我有连接两个摄像头，他们都是设备[0]和[1]。

然后，当你是一个Mac上，你可能会想使用的QuickTime观看视频，所以你需要确保你会做出兼容视频 - 这意味着使用-pix_fmt yuv420p。

ffmpeg -f avfoundation -i "2:0" -vf "crop=1024:768:400:800" -pix_fmt yuv420p -y -r 10 out.mov 

的1024×768的视频的宽度和高度，以及400：800在距屏幕的左上角，我想从记录偏移。