#!/bin/bash
# A simple script to grab a screencast of a window using ffmpeg
# Once started, select the window you want to record, and start 
# talking/using the indicated program

# Select window to grab info from
INFO=$(xwininfo -frame)

# Get the window size
WIN_SIZE=$(echo $INFO | grep -oEe 'geometry [0-9]+x[0-9]+' | grep -oEe '[0-9]+x[0-9]+')
# Get the window position
WIN_XY=$(echo $INFO | grep -oEe 'Corners: \+[0-9]+\+[0-9]+' | grep -oEe '[0-9]+\+[0-9]+' | sed -e 's/\+/,/')
# Determine window width and window height, and adjust to be divisible by two
WIN_WIDTH=$(echo $WIN_SIZE | cut -d "x" -f 1 | awk '{print $1+$1%2}')
WIN_HEIGHT=$(echo $WIN_SIZE | cut -d "x" -f 2 | awk '{print $1+$1%2}')

# Run ffmpeg
# Audio from alsa, using one channel, using the default pulse input device
# Video from X11, framerate 30
# Use the libx264 video encoder with the lossless_ultrafast preset
# Use the libmp3lame audio encoder
# Output to a file in the user's homedir, using current date and time

ffmpeg \
-f alsa -ac 1 -i pulse \
-f x11grab -r 30 -s ${WIN_WIDTH}x${WIN_HEIGHT} -i :0.0+${WIN_XY} \
-vcodec libx264 -vpre lossless_ultrafast \
-acodec libmp3lame \
${HOME}/screencast-$(date +%F-%H-%M-%S).mkv