参考:
ffmpeg：提取音视频、合并音视频
ffmpeg音视频合并拆分压缩
比如：
$ ffmpeg -i 九品芝麻官.BD.720p.国粤双语中字.mkv
ffmpeg version 4.2.4-1ubuntu0.1 Copyright (c) 2000-2020 the FFmpeg developers
built with gcc 9 (Ubuntu 9.3.0-10ubuntu2)
configuration: --prefix=/usr --extra-version=1ubuntu0.1 --toolchain=hardened --libdir=/usr/lib/x86_64-linux-gnu --incdir=/usr/include/x86_64-linux-gnu --arch=amd64 --enable-gpl --disable-stripping --enable-avresample --disable-filter=resample --enable-avisynth --enable-gnutls --enable-ladspa --enable-libaom --enable-libass --enable-libbluray --enable-libbs2b --enable-libcaca --enable-libcdio --enable-libcodec2 --enable-libflite --enable-libfontconfig --enable-libfreetype --enable-libfribidi --enable-libgme --enable-libgsm --enable-libjack --enable-libmp3lame --enable-libmysofa --enable-libopenjpeg --enable-libopenmpt --enable-libopus --enable-libpulse --enable-librsvg --enable-librubberband --enable-libshine --enable-libsnappy --enable-libsoxr --enable-libspeex --enable-libssh --enable-libtheora --enable-libtwolame --enable-libvidstab --enable-libvorbis --enable-libvpx --enable-libwavpack --enable-libwebp --enable-libx265 --enable-libxml2 --enable-libxvid --enable-libzmq --enable-libzvbi --enable-lv2 --enable-omx --enable-openal --enable-opencl --enable-opengl --enable-sdl2 --enable-libdc1394 --enable-libdrm --enable-libiec61883 --enable-nvenc --enable-chromaprint --enable-frei0r --enable-libx264 --enable-shared
libavutil 56. 31.100 / 56. 31.100
libavcodec 58. 54.100 / 58. 54.100
libavformat 58. 29.100 / 58. 29.100
libavdevice 58. 8.100 / 58. 8.100
libavfilter 7. 57.100 / 7. 57.100
libavresample 4. 0. 0 / 4. 0. 0
libswscale 5. 5.100 / 5. 5.100
libswresample 3. 5.100 / 3. 5.100
libpostproc 55. 5.100 / 55. 5.100
Input #0, matroska,webm, from '九品芝麻官.BD.720p.国粤双语中字.mkv':
Metadata:
encoder : libebml v1.0.0 + libmatroska v1.0.0
creation_time : 2015-09-19T14:26:58.000000Z
Duration: 01:46:44.22, start: 0.000000, bitrate: 1703 kb/s
Stream #0:0(chi): Video: h264 (High), yuv420p(progressive), 1280x720 [SAR 1:1 DAR 16:9], 24 fps, 24 tbr, 1k tbn, 48 tbc (default)
Stream #0:1(chi): Audio: aac (HE-AAC), 48000 Hz, stereo, fltp (default)
Metadata:
title : 粤语
Stream #0:2(chi): Audio: aac (HE-AAC), 48000 Hz, stereo, fltp
Metadata:
title : 国语
下面实现的功能是将上面的视频文件的视频流和国语音频流提取出来，合并成新的文件：
$ ffmpeg -i 九品芝麻官.BD.720p.国粤双语中字.mkv -vcodec copy -map 0:0 -acodec copy -map 0:2 b.mkv
查看输出文件格式信息：
$ ffmpeg -i b.mkv
ffmpeg version 4.2.4-1ubuntu0.1 Copyright (c) 2000-2020 the FFmpeg developers
built with gcc 9 (Ubuntu 9.3.0-10ubuntu2)
configuration: --prefix=/usr --extra-version=1ubuntu0.1 --toolchain=hardened --libdir=/usr/lib/x86_64-linux-gnu --incdir=/usr/include/x86_64-linux-gnu --arch=amd64 --enable-gpl --disable-stripping --enable-avresample --disable-filter=resample --enable-avisynth --enable-gnutls --enable-ladspa --enable-libaom --enable-libass --enable-libbluray --enable-libbs2b --enable-libcaca --enable-libcdio --enable-libcodec2 --enable-libflite --enable-libfontconfig --enable-libfreetype --enable-libfribidi --enable-libgme --enable-libgsm --enable-libjack --enable-libmp3lame --enable-libmysofa --enable-libopenjpeg --enable-libopenmpt --enable-libopus --enable-libpulse --enable-librsvg --enable-librubberband --enable-libshine --enable-libsnappy --enable-libsoxr --enable-libspeex --enable-libssh --enable-libtheora --enable-libtwolame --enable-libvidstab --enable-libvorbis --enable-libvpx --enable-libwavpack --enable-libwebp --enable-libx265 --enable-libxml2 --enable-libxvid --enable-libzmq --enable-libzvbi --enable-lv2 --enable-omx --enable-openal --enable-opencl --enable-opengl --enable-sdl2 --enable-libdc1394 --enable-libdrm --enable-libiec61883 --enable-nvenc --enable-chromaprint --enable-frei0r --enable-libx264 --enable-shared
libavutil 56. 31.100 / 56. 31.100
libavcodec 58. 54.100 / 58. 54.100
libavformat 58. 29.100 / 58. 29.100
libavdevice 58. 8.100 / 58. 8.100
libavfilter 7. 57.100 / 7. 57.100
libavresample 4. 0. 0 / 4. 0. 0
libswscale 5. 5.100 / 5. 5.100
libswresample 3. 5.100 / 3. 5.100
libpostproc 55. 5.100 / 55. 5.100
Input #0, matroska,webm, from 'b.mkv':
Metadata:
ENCODER : Lavf58.29.100
Duration: 01:46:44.22, start: 0.000000, bitrate: 1640 kb/s
Stream #0:0(chi): Video: h264 (High), yuv420p(progressive), 1280x720 [SAR 1:1 DAR 16:9], 24 fps, 24 tbr, 1k tbn, 48 tbc (default)
Metadata:
DURATION : 01:46:44.083000000
Stream #0:1(chi): Audio: aac (HE-AAC), 48000 Hz, stereo, fltp
Metadata:
title : 国语
DURATION : 01:46:44.223000000
交换国语和粤语音轨：
$ ffmpeg -i 九品芝麻官.BD.720p.国粤双语中字.mkv -vcodec copy -map 0:0 -acodec copy -map 0:2 -acodec copy -map 0:1 b.mkv
下面是音视频流的映射信息：
Input #0, matroska,webm, from '九品芝麻官.BD.720p.国粤双语中字.mkv':
Metadata:
encoder : libebml v1.0.0 + libmatroska v1.0.0
creation_time : 2015-09-19T14:26:58.000000Z
Duration: 01:46:44.22, start: 0.000000, bitrate: 1703 kb/s
Stream #0:0(chi): Video: h264 (High), yuv420p(progressive), 1280x720 [SAR 1:1 DAR 16:9], 24 fps, 24 tbr, 1k tbn, 48 tbc (default)
Stream #0:1(chi): Audio: aac (HE-AAC), 48000 Hz, stereo, fltp (default)
Metadata:
title : 粤语
Stream #0:2(chi): Audio: aac (HE-AAC), 48000 Hz, stereo, fltp
Metadata:
title : 国语
Output #0, matroska, to 'b.mkv':
Metadata:
encoder : Lavf58.29.100
Stream #0:0(chi): Video: h264 (High) (H264 / 0x34363248), yuv420p(progressive), 1280x720 [SAR 1:1 DAR 16:9], q=2-31, 24 fps, 24 tbr, 1k tbn, 1k tbc (default)
Stream #0:1(chi): Audio: aac (HE-AAC) ([255][0][0][0] / 0x00FF), 48000 Hz, stereo, fltp
Metadata:
title : 国语
Stream #0:2(chi): Audio: aac (HE-AAC) ([255][0][0][0] / 0x00FF), 48000 Hz, stereo, fltp (default)
Metadata:
title : 粤语
Stream mapping:
Stream #0:0 -> #0:0 (copy)
Stream #0:2 -> #0:1 (copy)
Stream #0:1 -> #0:2 (copy)
查看格式信息：
$ ffmpeg -i b.mkv
ffmpeg version 4.2.4-1ubuntu0.1 Copyright (c) 2000-2020 the FFmpeg developers
built with gcc 9 (Ubuntu 9.3.0-10ubuntu2)
configuration: --prefix=/usr --extra-version=1ubuntu0.1 --toolchain=hardened --libdir=/usr/lib/x86_64-linux-gnu --incdir=/usr/include/x86_64-linux-gnu --arch=amd64 --enable-gpl --disable-stripping --enable-avresample --disable-filter=resample --enable-avisynth --enable-gnutls --enable-ladspa --enable-libaom --enable-libass --enable-libbluray --enable-libbs2b --enable-libcaca --enable-libcdio --enable-libcodec2 --enable-libflite --enable-libfontconfig --enable-libfreetype --enable-libfribidi --enable-libgme --enable-libgsm --enable-libjack --enable-libmp3lame --enable-libmysofa --enable-libopenjpeg --enable-libopenmpt --enable-libopus --enable-libpulse --enable-librsvg --enable-librubberband --enable-libshine --enable-libsnappy --enable-libsoxr --enable-libspeex --enable-libssh --enable-libtheora --enable-libtwolame --enable-libvidstab --enable-libvorbis --enable-libvpx --enable-libwavpack --enable-libwebp --enable-libx265 --enable-libxml2 --enable-libxvid --enable-libzmq --enable-libzvbi --enable-lv2 --enable-omx --enable-openal --enable-opencl --enable-opengl --enable-sdl2 --enable-libdc1394 --enable-libdrm --enable-libiec61883 --enable-nvenc --enable-chromaprint --enable-frei0r --enable-libx264 --enable-shared
libavutil 56. 31.100 / 56. 31.100
libavcodec 58. 54.100 / 58. 54.100
libavformat 58. 29.100 / 58. 29.100
libavdevice 58. 8.100 / 58. 8.100
libavfilter 7. 57.100 / 7. 57.100
libavresample 4. 0. 0 / 4. 0. 0
libswscale 5. 5.100 / 5. 5.100
libswresample 3. 5.100 / 3. 5.100
libpostproc 55. 5.100 / 55. 5.100
Input #0, matroska,webm, from 'b.mkv':
Metadata:
ENCODER : Lavf58.29.100
Duration: 01:46:44.22, start: 0.000000, bitrate: 1705 kb/s
Stream #0:0(chi): Video: h264 (High), yuv420p(progressive), 1280x720 [SAR 1:1 DAR 16:9], 24 fps, 24 tbr, 1k tbn, 48 tbc (default)
Metadata:
DURATION : 01:46:44.083000000
Stream #0:1(chi): Audio: aac (HE-AAC), 48000 Hz, stereo, fltp
Metadata:
title : 国语
DURATION : 01:46:44.223000000
Stream #0:2(chi): Audio: aac (HE-AAC), 48000 Hz, stereo, fltp (default)
Metadata:
title : 粤语
DURATION : 01:46:44.223000000
完。