Zmodo Viewer, bash: View multiple cams in a grid with MPlayer

zcam.sh

#!/bin/bash
server="securitysystem" # my router-defined hostname for my dvr, use ip instead
port=8000
res_x=960 # cam resolution, mine is 960H grabbed from running show_cam once w/o -really-silent and watching the output 
res_y=480
cams=(1 3 4) #show cams 1, 3, and 4, skipping 2 since mine isn't connected

function get_current_workspace() {
   workspace=`wmctrl -d | grep '*' | cut -d ' ' -f1`
}

function move_to_workspace() {
  local window_id=`wmctrl -lp | grep $1 | awk '{print $1}'`
  echo "Moving window $window_id (PID: $1) to workspace $workspace"
  wmctrl -i -r $window_id -t $workspace
}

function set_screen_res() {
  screenx=$(xrandr --current | grep '*' | uniq | awk '{print $1}' | cut -d 'x' -f1)
  screeny=$(xrandr --current | grep '*' | uniq | awk '{print $1}' | cut -d 'x' -f2)
}
function set_grid() { # args: $1 = number of cams, $2 = round to nearest
  local grid_size=$(( (($1 + $2 - 1) / $2) * $2 ))
  cols=$(( $grid_size / 2 )) # if you wanted, you could set a custom number of columns per row
  rows=$(( $grid_size / $cols )) # and a custom number of rows
}
function do_math(){ # does math in floating point and returns a regular int
  last_math=`echo "scale=6; x=$1; scale=0; x / 1" | bc`;
}

function set_cam_dimensions() { #  resize cams so they fit into their cell size, maintaining aspect ratio
  local cell_x=$(( $screenx / $cols ))
  local cell_y=$(( $screeny / $rows  ))
  do_math "(($cell_x / $cell_y) > ($res_x / $res_y))"
  if [ $last_math -eq 1 ]; then
    cam_y=$(( $cell_y ))
    do_math "($cell_y / $res_y) * $res_x"
    cam_x=$(( $last_math ))
  else
    cam_x=$(( $cell_x ))
    do_math "($cell_x / $res_x) * $res_y"
    cam_y=$(( $last_math ))
  fi
}
function show_cam() { # args: $1 = cam number, $2 = x position, #3 = y position
  local cam=$(($1 - 1))
  # send header requesting 720p stream for $cam
  # then trim first 12 bytes of received data, which is only an echo of what we sent
  # then add magic bytes to identify as the first NAL unit the h264 stream
  # finally, open borderless mplayer in stdin mode, with specific position and dimensions
  echo "Requesting cam $cam at $server:$port $cam_x by $cam_y $2:$3"
  echo -ne "\x55\x55\xaa\xaa\x00\x00\x00\x00\x00\x$cam\x00\x50" \
    | nc $server $port \
    | tail -c +12 \
    | (echo -ne '\x00\x00\x00\x01' && cat) \
    | mplayer -really-quiet -noborder -demuxer h264es -x $cam_x -y $cam_y -geometry "$2:$3" -fps 25 - &
  # mplayer is run in background to get it's PID, used to move to initial workspace
  # then we go back to synchrous mode by waiting on that PID
  local job_id=$!
  sleep 1
  move_to_workspace $job_id
  wait $job_id
    
}
function show_cam_persist() { # re-open cam if connection is lost
  while true; do
    show_cam $2 $3 $4
    if kill -0 $1 > /dev/null 2>&1 ; then # check parent process still exists
      echo "Cam connection closed, checking again in 10 seconds"
      sleep 10 # Zmodo DVR disconnects around midnight fsr, blocks connections that happen too soon after that.
      # i've experimented with 1s and 5s, both lead to infinite disconnects/reconnects. 10s works
    else
      echo "Parent process killed, ending session"
      break
    fi
  done
}
function main() { # args: $1 = parent PID, $2: boolean = persist
  local row=0
  local col=0
  local index=0
  local posx=0;
  local posy=0;

  for i in ${cams[@]}; do
    row=$(( $index / $cols ))
    col=$(( $index % $cols ))
    posx=$(( $col * $cam_x ))
    posy=$(( ($row * $cam_y) + 48 )) # offset y position by height of gnome title bar
    if $2; then
      show_cam_persist $1 $i $posx $posy &
    else
      show_cam $i $posx $posy &
    fi
    index=$(( $index + 1 ))
  done
}

get_current_workspace
set_screen_res
set_grid ${#cams[@]} 4 # 1-4 cams = 4 cells, 4-8 = 8 cells total, etc.
set_cam_dimensions

if [ "$1" == "--persist" ]; then
  persist=true
else
  persist=false
fi

main $$ $persist

wait

3-cam example. If you plan on having these running 24/7, I recommend you keep them in their own workspace. Run with --persist argument to reopen cams if connection closes.