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I want to know how can I only capture desktop audio (means no mic!).

I am using this command:

$ ffmpeg -f x11grab -s 1360x768 -r 30 -i :0.0 -preset ultrafast ~/Videos/out.mp4
ffmpeg version 2.4.3-1ubuntu1~trusty6 Copyright (c) 2000-2014 the FFmpeg developers
  built on Nov 22 2014 17:07:19 with gcc 4.8 (Ubuntu 4.8.2-19ubuntu1)
  configuration: --prefix=/usr --extra-version='1ubuntu1~trusty6' --build-suffix=-ffmpeg --toolchain=hardened --extra-cflags= --extra-cxxflags= --libdir=/usr/lib/x86_64-linux-gnu --shlibdir=/usr/lib/x86_64-linux-gnu --incdir=/usr/include/x86_64-linux-gnu --enable-gpl --enable-shared --disable-stripping --enable-avresample --enable-avisynth --enable-fontconfig --enable-gnutls --enable-ladspa --enable-libass --enable-libbluray --enable-libbs2b --enable-libcaca --enable-libcdio --enable-libflite --enable-libfreetype --enable-libfribidi --enable-libgme --enable-libgsm --enable-libmodplug --enable-libmp3lame --enable-libopenjpeg --enable-libopus --enable-libpulse --enable-librtmp --enable-libschroedinger --enable-libshine --enable-libspeex --enable-libssh --enable-libtheora --enable-libtwolame --enable-libvorbis --enable-libvpx --enable-libwavpack --enable-libwebp --enable-opengl --enable-x11grab --enable-libxvid --enable-libx265 --enable-libdc1394 --enable-libiec61883 --enable-libzvbi --enable-libzmq --enable-frei0r --enable-libx264 --enable-libsoxr --enable-openal --enable-libopencv
  libavutil      54.  7.100 / 54.  7.100
  libavcodec     56.  1.100 / 56.  1.100
  libavformat    56.  4.101 / 56.  4.101
  libavdevice    56.  0.100 / 56.  0.100
  libavfilter     5.  1.100 /  5.  1.100
  libavresample   2.  1.  0 /  2.  1.  0
  libswscale      3.  0.100 /  3.  0.100
  libswresample   1.  1.100 /  1.  1.100
  libpostproc    53.  0.100 / 53.  0.100
[x11grab @ 0x16051e0] device: :0.0 -> display: :0.0 x: 0 y: 0 width: 1360 height: 768
[x11grab @ 0x16051e0] shared memory extension found
Input #0, x11grab, from ':0.0':
  Duration: N/A, start: 1444234613.435347, bitrate: 1002700 kb/s
    Stream #0:0: Video: rawvideo (BGR[0] / 0x524742), bgr0, 1360x768, 1002700 kb/s, 30 tbr, 1000k tbn, 30 tbc
File '/home/elderzz/Videos/out.mp4' already exists. Overwrite ? [y/N] ^A

I can capture mic with another app, but I need the mic audio to be in a different file. I only want to capture desktop audio!

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2 Answers 2

Reset to default
25

pavucontrol

enter image description here

  1. Install pavucontrol.
  2. Start recording with ffmpeg (see example commands below).
  3. Start pavucontrol.
  4. Go to the Recording tab and you'll find ffmpeg or Lavf56.15.102 (or similar) listed there.
  5. Change audio capture from Internal Audio Analog Stereo to Monitor of Internal Audio Analog Stereo.

Now it should record system and application audio instead of the microphone.

This setting will be remembered. The next time you want to capture with ffmpeg, it will automatically start recording system audio. If you want to revert this, use pavucontrol again to change back to microphone input.

The text above was adapted from HOWTO: Screencasting on Linux.

example ffmpeg commands

audio only

ffmpeg -f pulse -i default output.wav

with screen capture

ffmpeg -f x11grab -video_size 1360x768 -framerate 30 -i :0.0 -f pulse -i default -preset ultrafast -crf 18 -pix_fmt yuv420p out.mkv
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  • Will this recording be lossless?
    – Anmol Singh Jaggi
    Commented Jun 21, 2016 at 19:38
  • @AnmolSinghJaggi No. -crf 18 is lossy, and there is also loss due to RGB to YUV 4:2:0 colorspace conversion.
    – llogan
    Commented Jun 21, 2016 at 20:33
  • No I was talking about the audio only part.
    – Anmol Singh Jaggi
    Commented Jun 21, 2016 at 21:13
  • 1
    @AnmolSinghJaggi Yes, the audio should be lossless.
    – llogan
    Commented Jun 21, 2016 at 21:52
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    If you do not want to switch the source manually, you can use the command pactl list soruces to figure out the internal name of the monitor source and then use -f pulse -i NAME instead of default, e.g. -f pulse -i alsa_output.pci-0000_00_1f.3.analog-stereo.monitor The exact name will differ from system to system.
    – regnarg
    Commented Apr 3, 2020 at 14:33
1

You can also record to compressed MP3 (with a bit rate of your choice) such as:

ffmpeg -f alsa -ac 2 -i default -acodec libmp3lame -ab 320k ouput.mp3
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