How to use GoPlantUML?
goplantuml generates code in PlantUML format that represents a diagram of the relationships between the Go receiver structs, they are analogous to …
ffmpeg is a cli-tool that in addition to allowing multimedia file format conversion you can also record screen video starting from the terminal interface.
I wrote this tutorial with the version n4.1.4, to know it use the flag -version:
$ ffmpeg -version
ffmpeg version n4.1.4 Copyright (c) 2000-2019 the FFmpeg developers
built with gcc 7 (Ubuntu 7.4.0-1ubuntu1~18.04.1)
configuration: --prefix= --prefix=/usr --disable-debug --disable-doc --disable-static --enable-avisynth --enable-cuda --enable-cuvid --enable-libdrm --enable-ffplay --enable-gnutls --enable-gpl --enable-libass --enable-libfdk-aac --enable-libfontconfig --enable-libfreetype --enable-libmp3lame --enable-libopencore_amrnb --enable-libopencore_amrwb --enable-libopus --enable-libpulse --enable-sdl2 --enable-libspeex --enable-libtheora --enable-libtwolame --enable-libv4l2 --enable-libvorbis --enable-libvpx --enable-libx264 --enable-libx265 --enable-libxcb --enable-libxvid --enable-nonfree --enable-nvenc --enable-omx --enable-openal --enable-opencl --enable-runtime-cpudetect --enable-shared --enable-vaapi --enable-vdpau --enable-version3 --enable-xlib
libavutil 56. 22.100 / 56. 22.100
libavcodec 58. 35.100 / 58. 35.100
libavformat 58. 20.100 / 58. 20.100
libavdevice 58. 5.100 / 58. 5.100
libavfilter 7. 40.101 / 7. 40.101
libswscale 5. 3.100 / 5. 3.100
libswresample 3. 3.100 / 3. 3.100
libpostproc 55. 3.100 / 55. 3.100
Record only video
Get a .mp4 file ideal for generic players:
$ ffmpeg -f x11grab -r 30 -s 1024x768 -i :0.0 record1.mp4
Explanation:
ffmpeg // we init ffmpeg
-f x11grab // source for the screen
-r 30 // frames per seconds
-s 1024x768 // screen resolution
-i :0.0 // screen input
record1.mp4 // title of video with its respective format
You can add -pix_fmt yuv420p, it makes the ffmpeg output in a standar pixel format that all players can display:
$ ffmpeg -f x11grab -r 30 -s 1024x768 -i :0.0 -pix_fmt yuv420p output.mp4
Record video with internal audio and microphone
Firts, you need to know the audio sources with $ ffmpeg -sources command, then it will show you with * for alsa (if installed) or pulse (pulseaudio), example:
$ ffmpeg -sources
Auto-detected sources for pulse:
* alsa_output.pci-0000_00_1b.0.analog-stereo.monitor [Monitor of Audio Interno Estéreo analógico]
alsa_input.pci-0000_00_1b.0.analog-stereo [Audio Interno Estéreo analógico]
alsa_output.pci-0000_01_00.0.analog-stereo.monitor [Monitor of CMI8738/CMI8768 PCI Audio (CMI8738/C3DX PCI Audio Device) Estéreo analógico]
alsa_input.pci-0000_01_00.0.analog-stereo [CMI8738/CMI8768 PCI Audio (CMI8738/C3DX PCI Audio Device) Estéreo analógico]
If you check with the graphical audio mixer, you will see that audio input is received from the microphone in ‘Analog Stereo Internal Audio’.
ffmpeg // we init ffmpeg
-f pulse // audio backend instance
-i alsa_input.pci-0000_00_1b.0.analog-stereo // select the first audio source
-f pulse // instantiate the audio backend again
-i alsa_output.pci-0000_00_1b.0.analog-stereo.monitor // seleccione segunda fuente de audio
-f x11grab // source for the screen
-r 30 // fps (sometimes it can be 60)
-s 1024x768 // screen resolution
-i :0.0 // screen input
-c:a mp3 // audio codec (tt's not necesary)
-b:i 5M // recording speed (5mps)
-ac 2 // audio channels (2 for estereo, although it already comes like this by default)
-async 25 // audio and video sync (sometimes 1 or 1000 recommended)
-filter_complex amix=inputs=2 // synchronize the two audio sources
-pix_fmt yuv420p // standard pixel format that all players can show
record1.mkv // name of the video with its respective format
- Version 1 (it worked):
$ ffmpeg -f pulse -i alsa_input.pci-0000_00_1b.0.analog-stereo -f x11grab -r 30 -s 1024x768 -i :0.0 -ac 2 -async 25 -filter_complex amix=inputs=1 record3.mp4
It records microphone audio fine but not internal audio, eg: playback from YouTube.
- Version 2 (it worked):
$ ffmpeg -f pulse -i alsa_input.pci-0000_00_1b.0.analog-stereo -f pulse -i alsa_output.pci-0000_00_1b.0.analog-stereo.monitor -f x11grab -r 30 -s 1024x768 -i :0.0 -ac 2 -async 25 -filter_complex amix=inputs=2 record1.mp4
Record both audios.
- Version 3 (it worked):
$ ffmpeg -f pulse -i alsa_input.pci-0000_00_1b.0.analog-stereo -f x11grab -r 60 -s 1024x768 -i :0.0 -ac 2 -async 25 -filter_complex amix=inputs=2 record2.mp4
Sure by -filter_complex amix=inputs=2 since there are not two audio sources.
References
Purga Linux. (2020, January 7). Grabar pantalla, micro y audio interno con FFMPEG [Video]. YouTube. https://www.youtube.com/watch?v=vJ5WznUk4Qs
How to Install and Use FFmpeg on Ubuntu 18.04. (2019, December 20). Linuxize. https://linuxize.com/post/how-to-install-ffmpeg-on-ubuntu-18-04/
Use -pix_fmt yuv420p to forced ffmpeg’s output to a standard pixel format that all players can show: https://stackoverflow.com/questions/44102207/ffplay-shows-video-but-ffmpeg-just-shows-black
engineerRed. (2019, March 16). ffmpeg black screen recording [Comment on the article “ffmpeg black screen recording”]. Ask Ubuntu. https://askubuntu.com/a/1126289
