1. 使用ffmpeg的filter_complex，colorkey和vn结果

./ffmpeg -i likeyou.mp4 -i adium.png -filter_complex "[1:v]colorkey=0x3BBD1E:0.1:0.2[ckout0];[0:v][ckout0]overlay=x=W-w-11:y=10"  -vn -report  -t 10 -y -f flv test_out1.flv139 [flv @ 0x4459fa0] intra_quant_bias = 0 inter_quant_bias = -64140 Output #0, flv, to 'test_out1.flv':141   Metadata:142     major_brand     : isom143     minor_version   : 1144     compatible_brands: isomavc1145     encoder         : Lavf57.25.100146     Stream #0:0, 0, 1/1000: Video: flv1 (flv) ([2][0][0][0] / 0x0002), yuv420p, 640x360 [SAR 1:1 DAR 16:9], q=2-31, 200 kb/s, 25 fps, 1k tbn, 25 tbc (default)147     Metadata:148       encoder         : Lavc57.24.102 flv149     Side data:150       unknown side data type 10 (24 bytes)151     Stream #0:1(und), 0, 1/1000: Audio: mp3 (libmp3lame) ([2][0][0][0] / 0x0002), 44100 Hz, stereo, fltp (default)152     Metadata:153       creation_time   : 2014-03-13 21:31:57154       handler_name    : sound155       encoder         : Lavc57.24.102 libmp3lame156 Stream mapping:157   Stream #0:0 (h264) -> overlay:main (graph 0)158   Stream #1:0 (png) -> colorkey (graph 0)159   overlay (graph 0) -> Stream #0:0 (flv)160   Stream #0:1 -> #0:1 (aac (native) -> mp3 (libmp3lame))

使用ffprobe分析输出视频

./ffprobe test_out1.flv
ffprobe version 3.0-static32: Copyright (c) 2007-2016 the FFmpeg developers32:configuration: --enable-gpl --enable-nonfree --disable-shared --enable-postproc --enable-bzlib --enable-zlib --enable-parsers --enable-libx264 --enable-libx265 --enable-libmp3lame --enable-libfaac --enable-libfdk-aac --enable-pthreads --extra-ldflags=-static --disable-ffserver --enable-ffplay --enable-asm --enable-yasm --enable-optimizations --pkg-config-flags=--static --extra-cflags=--static --extra-version=static --enable-libspeex --extra-ldflags=-L/usr/local/lib --extra-cflags=-I/usr/local/include --extra-libs=-lrtmplibavutil      55. 17.103 / 55. 17.103built with gcc 4.4.7 (GCC) 20120313 (Red Hat 4.4.7-16)libavcodec     57. 24.102 / 57. 24.102libavformat    57. 25.100 / 57. 25.100libavdevice    57.  0.101 / 57.  0.101libavfilter     6. 31.100 /  6. 31.100libswscale      4.  0.100 /  4.  0.100libswresample   2.  0.101 /  2.  0.101libpostproc    54.  0.100 / 54.  0.100
[flv @ 0x30202e0] decoding video .......
Input #0, flv, from 'test_out1.flv':Metadata:major_brand     : isomminor_version   : 1compatible_brands: isomavc1encoder         : Lavf57.25.10032:Duration: 00:00:10.0032:, start: 0.00000032:, bitrate: 603 kb/s32:Stream #0:0: Video: flv1, yuv420p, 640x360, 200 kb/s, 25 fps, 25 tbr, 1k tbn, 1k tbcStream #0:1: Audio: mp3, 44100 Hz, stereo, s16p, 128 kb/s

结论：

即使设置了vn，但是在有滤镜的情况下，仍然会输出视频数据。

2. 有vn，没有滤镜

./ffmpeg -i likeyou.mp4 -i adium.png -vn -report  -t 10 -y -f flv test_out1.flv -v 48103 [AVFilterGraph @ 0x26ff340] query_formats: 5 queried, 12 merged, 0 already done, 0 delayed104 Output #0, flv, to 'test_out1.flv':105   Metadata:106     major_brand     : isom107     minor_version   : 1108     compatible_brands: isomavc1109     encoder         : Lavf57.25.100110     Stream #0:0(und), 0, 1/1000: Audio: mp3 (libmp3lame) ([2][0][0][0] / 0x0002), 44100 Hz, stereo, fltp (default)111     Metadata:112       creation_time   : 2014-03-13 21:31:57113       handler_name    : sound114       encoder         : Lavc57.24.102 libmp3lame115 Stream mapping:116   Stream #0:1 -> #0:0 (aac (native) -> mp3 (libmp3lame))

3. 没有滤镜，没有vn

./ffmpeg -i likeyou.mp4 -i adium.png -report  -t 10 -y -f flv test_out1.flv -v 48114 [flv @ 0x30a9e80] intra_quant_bias = 0 inter_quant_bias = -64115 Output #0, flv, to 'test_out1.flv':116   Metadata:117     major_brand     : isom118     minor_version   : 1119     compatible_brands: isomavc1120     encoder         : Lavf57.25.100121     Stream #0:0(und), 0, 1/1000: Video: flv1 (flv), 1 reference frame ([2][0][0][0] / 0x0002), yuv420p(left), 640x360 [SAR 1:1 DAR 16:9], 1/25, q=2-31, 200 kb/s, 25 fps, 1k tbn, 25 tbc (default)122     Metadata:123       creation_time   : 2014-03-13 21:31:56124       handler_name    : video125       encoder         : Lavc57.24.102 flv126     Side data:127       unknown side data type 10 (24 bytes)128     Stream #0:1(und), 0, 1/1000: Audio: mp3 (libmp3lame) ([2][0][0][0] / 0x0002), 44100 Hz, stereo, fltp (default)129     Metadata:130       creation_time   : 2014-03-13 21:31:57131       handler_name    : sound132       encoder         : Lavc57.24.102 libmp3lame133 Stream mapping:134   Stream #0:0 -> #0:0 (h264 (native) -> flv1 (flv))135   Stream #0:1 -> #0:1 (aac (native) -> mp3 (libmp3lame))