Creating & Programming Robots

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**ffmpeg** is a very powerful command line tool to manipulate audio and video. Here are some command to acquire, cut, split, copy, transcode, compose video and audio files. The following commands assume using Linux.

To capture the content of a part of a the screen of   with the upper left corner x=50,y=150  :
<code bash>
ffmpeg -video_size 1024x768 -framerate 25 -f x11grab -i :0.0+50,150 output.mp4
</code>

To capture the content of a specific window, it's a bit complicated on linux as we can use the window's title (-title argurment). So, we first need to know the id of the window :
<code bash>
wmctrl -l
0x02200002  0 rizen5 XdndCollectionWindowImp
0x02200003  0 rizen5 unity-launcher
0x02200004  0 rizen5 unity-panel
0x02200005  0 rizen5 unity-dash
0x02200006  0 rizen5 Hud
0x01a0000a -1 rizen5 Desktop
0x058000af  0 rizen5 emacs@rizen5
0x06400015  0    N/A V-REP PRO EDU - New file - rendering: 2 ms (8.0 fps) - SIMULATION STOPPED
</code>
The first field is the id of the windows. For example, here, we will record the content of the V-REP window, so the id is 0x06400015. The location on the screen and the size of the window is given by :
<code bash>
xwininfo -shape -id 0x06400015

xwininfo: Window id: 0x6400015 "V-REP PRO EDU - New file - rendering: 2 ms (8.0 fps) - SIMULATION STOPPED"

  Absolute upper-left X:  241
  Absolute upper-left Y:  196
  Relative upper-left X:  0
  Relative upper-left Y:  0
  Width: 1545
  Height: 810
  Depth: 24
  Visual: 0x27
  Visual Class: TrueColor
  Border width: 0
  Class: InputOutput
  Colormap: 0x6400014 (not installed)
  Bit Gravity State: NorthWestGravity
  Window Gravity State: NorthWestGravity
  Backing Store State: NotUseful
  Save Under State: no
  Map State: IsViewable
  Override Redirect State: no
  Corners:  +241+196  -134+196  -134-74  +241-74
  -geometry 1545x810+241-74

  No window shape defined
  No border shape defined
</code>

The window as a size of 1545x810 and starts at (241,196)
<code bash>
ffmpeg -video_size 1545x810 -framerate 25 -f x11grab -i :0.0+241,196 output.mp4
</code>

It can be wise to change to a common video display size , e.g. 1366x768, 1600x900 or 1920x1200. this can be done
by either two ways, using the name (title) of the window :
<code bash>
# change the size and location
wmctrl -r "V-REP PRO EDU" -e 0,100,100,1600,900
# or change only size
xdotool search --name "V-REP PRO EDU" windowsize 1600 900

# when not working with window's name (not resizing the right window)
# use id instead of name
wmctrl -i -r 0x06800015 -e 0,100,100,1600,900
</code>

Then do not forget to re run **xwininfo** as the location and the size might have been changed by the display manager.

Get the audio device:
<code bash> 
arecord -l
</code> 
<code text> 
**** List of CAPTURE Hardware Devices ****
card 1: Device [USB Audio Device], device 0: USB Audio [USB Audio]
  Subdevices: 1/1
  Subdevice #0: subdevice #0
card 2: Generic [HD-Audio Generic], device 0: ALC892 Analog [ALC892 Analog]
  Subdevices: 1/1
  Subdevice #0: subdevice #0
card 2: Generic [HD-Audio Generic], device 2: ALC892 Alt Analog [ALC892 Alt Analog]
  Subdevices: 1/1
  Subdevice #0: subdevice #0
</code> 


Recording 30 seconds with with audio:
<code bash> 
xcorn=100
ycorn=80
duration=00:00:30
soundcard=hw:2 # hw:1
nbchan=2 # 1
ffmpeg -y -video_size 1600x900 -f x11grab -i ${DISPLAY}.0+${xcorn},${ycorn} -f alsa -thread_queue_size 16384 -ac ${nbchan} -i ${soundcard} -acodec aac -strict experimental -t ${duration} ./output.mp4
</code>

Fullscreen recording with audio for 30 seconds:
<code bash> 
duration=00:00:30
soundcard=hw:2 # hw:1
nbchan=2 # 1
ffmpeg -y -video_size 1920x1050 -f x11grab -i ${DISPLAY}.0+0,0 -f alsa -thread_queue_size 16384 -ac ${nbchan} -i ${soundcard} -acodec aac -strict experimental -t ${duration} ./output.mp4
</code>

It may turn out that it does not record anything in the audio channel ?!? in this case you can try **pulse** :

<code bash> 
duration=00:00:30
nbchan=2 # 1
ffmpeg -y -video_size 1920x1050 -f x11grab -i ${DISPLAY}.0+0,0 -f alsa -thread_queue_size 16384 -ac ${nbchan} -i pulse  -t ${duration} ./output.mp4
</code>




Comprehensive information is available in the [[https://trac.ffmpeg.org/wiki|ffmpeg wiki]].

Back to [[ffmpeg:main-ffmpeg|top]].