ffmpeg下载地址：http://ffmpeg.zeranoe.com/builds/
参数说明：
-i表示输入文件
-acodec copy -vcodec copy 表示音频、视频不进行编解码，直接复制源视频
-ss表示起始时间，-t表示时长，格式均为“小时：分钟：秒”
-t：截取视频的结束时间
输入测试命令：
./ffmpeg -y -i ../../ca4bedca5d034d3f8cb0353e1efc68be.mp4 -ss 00:10:00.0 -acodec copy -vcodec copy -async 1 ../../aa.mp4
输出：
ffmpeg version git-2020-03-12-675bb1f Copyright (c) 2000-2020 the FFmpeg developers
built with Apple clang version 11.0.0 (clang-1100.0.33.8)
configuration: --enable-gpl --enable-version3 --enable-sdl2 --enable-fontconfig --enable-gnutls --enable-iconv --enable-libass --enable-libdav1d --enable-libbluray --enable-libfreetype --enable-libmp3lame --enable-libopencore-amrnb --enable-libopencore-amrwb --enable-libopenjpeg --enable-libopus --enable-libshine --enable-libsnappy --enable-libsoxr --enable-libtheora --enable-libtwolame --enable-libvpx --enable-libwavpack --enable-libwebp --enable-libx264 --enable-libx265 --enable-libxml2 --enable-libzimg --enable-lzma --enable-zlib --enable-gmp --enable-libvidstab --enable-libvorbis --enable-libvo-amrwbenc --enable-libmysofa --enable-libspeex --enable-libxvid --enable-libaom --enable-appkit --enable-avfoundation --enable-coreimage --enable-audiotoolbox
libavutil 56. 42.100 / 56. 42.100
libavcodec 58. 75.100 / 58. 75.100
libavformat 58. 41.100 / 58. 41.100
libavdevice 58. 9.103 / 58. 9.103
libavfilter 7. 77.100 / 7. 77.100
libswscale 5. 6.101 / 5. 6.101
libswresample 3. 6.100 / 3. 6.100
libpostproc 55. 6.100 / 55. 6.100
Input #0, mov,mp4,m4a,3gp,3g2,mj2, from '../../ca4bedca5d034d3f8cb0353e1efc68be.mp4':
Metadata:
major_brand : isom
minor_version : 512
compatible_brands: isomiso2avc1mp41
encoder : Lavf57.71.100
Duration: 02:16:47.08, start: 0.000000, bitrate: 710 kb/s
Stream #0:0(und): Video: h264 (High) (avc1 / 0x31637661), yuv420p, 640x1130 [SAR 113:36 DAR 16:9], 639 kb/s, 25 fps, 25 tbr, 90k tbn, 50 tbc (default)
Metadata:
handler_name : VideoHandler
Stream #0:1(und): Audio: aac (LC) (mp4a / 0x6134706D), 44100 Hz, stereo, fltp, 64 kb/s (default)
Metadata:
handler_name : SoundHandler
Output #0, mp4, to '../../aa.mp4':
Metadata:
major_brand : isom
minor_version : 512
compatible_brands: isomiso2avc1mp41
encoder : Lavf58.41.100
Stream #0:0(und): Video: h264 (High) (avc1 / 0x31637661), yuv420p, 640x1130 [SAR 113:36 DAR 16:9], q=2-31, 639 kb/s, 25 fps, 25 tbr, 90k tbn, 90k tbc (default)
Metadata:
handler_name : VideoHandler
Stream #0:1(und): Audio: aac (LC) (mp4a / 0x6134706D), 44100 Hz, stereo, fltp, 64 kb/s (default)
Metadata:
handler_name : SoundHandler
Stream mapping:
Stream #0:0 -> #0:0 (copy)
Stream #0:1 -> #0:1 (copy)
Press [q] to stop, [?] for help
frame=42219 fps=0.0 q=-1.0 size= 145152kB time=00:28:09.86 bitrate= 703.7kbits/frame=89329 fps=89329 q=-1.0 size= 306688kB time=00:59:34.41 bitrate= 702.9kbitframe=135368 fps=90245 q=-1.0 size= 465408kB time=01:30:15.94 bitrate= 704.0kbiframe=180497 fps=90248 q=-1.0 size= 620032kB time=02:00:21.11 bitrate= 703.4kbiframe=190144 fps=87433 q=-1.0 Lsize= 660361kB time=02:06:47.04 bitrate= 711.1kbits/s speed=3.5e+03x
video:593743kB audio:59757kB subtitle:0kB other streams:0kB global headers:0kB muxing overhead: 1.049856%
例子：
剪切的同时，格式不变，音视频参数不变：
ffmpeg -y -i bb.mp4 -ss 00:00:00.0 -t 00:01:00.0 -acodec copy -vcodec copy -async 1 aa.mp4
剪切的同时，音视频参数不变，只转换格式：
ffmpeg -y -i bb.mp4 -ss 00:00:00.0 -t 00:01:00.0 -acodec copy -vcodec copy -async 1 aa.flv
剪切的同时，格式不变，只转换音视频参数：
ffmpeg -y -i bb.mp4 -ss 00:00:00.0 -t 00:01:00.0 -ab 56k -ar 44100 -b:v 2200k -r 29.97 -s 640x360 aa.mp4
剪切的同时，既转换格式又转换音视频参数：
ffmpeg -y -i bb.mp4 -ss 00:00:00.0 -t 00:01:00.0 -ab 56k -ar 44100 -b:v 2200k -r 29.97 -s 640x360 aa.flv
