How to put a webcam recording and a desktop recording side by side with ffmpeg

Question

I want to directly put 2 ffmpeg outut side by side in order to output a video that has both videos.

The recording ares

1. a 640x480 webcam recording with:

   ffmpeg -f v4l2 -framerate 25 -video_size 640x480 -i /dev/video0 webcam.mkv
   

2. a desktop recording video of 1600x900 with

   ffmpeg -f x11grab -r 100 -s 1600x900 -i :0.0 -acodec pcm_s16le -vcodec libx264 -preset ultrafast -threads 3 desktop.mkv
   
                 ---------------
                 |             |
      |----------|   desktop   |
      |  webcam  |             |
      --------------------------
   

Answer 1

ffmpeg \
-f v4l2 -framerate 25 -video_size 640x480 -i /dev/video0 \
-f x11grab -framerate 100 -video_size 1600x900 -i :0.0 \
-filter_complex "[0:v]pad=iw:900:0:(oh-ih)/2[left];[left][1:v]hstack" \
output

• Use -framerate instead of -r and -video_size instead of -s for x11grab.
• The hstack filter will use the frame rate of the first input, so you may add the fps filter after the pad filter if desired.
• -framerate 100 seems high and may not be sustainable.