Take a bunch of input video clips and turn them into a video mosaic

clips_to_mosaic.sh

#######################
#  clips_to_mosaic.sh #
#  Requires ffmpeg    #
#######################

# This file contains video paths, one per line
FILE="infile.txt"

# Square tile size (pixels)
TILE_SIDE=108
# Video tiles are populated top-to-bottom and left-to-right
TILE_COLS=16

# "Initialize" vars
INPUTS=""
SOURCES=""
LAYERS=""
COUNTER=0
while read line
do
	# Prevent appending `[tmpX];` to first and last layer
	if [ $(($COUNTER)) -ne 0 ]
	then
		LAYERS+=" [tmp$(($COUNTER))]; "
	fi

	INPUTS+="-i $line "

	# ~> [3:v] setpts=PTS-STARTPTS, scale=128x128 [stream3];
	SOURCES+="[$COUNTER:v] setpts=PTS-STARTPTS, scale=$(($TILE_SIDE))x$(($TILE_SIDE)) [stream$COUNTER]; "

	# ~> [tmp3][stream3] overlay=shortest=1:x=324:y=0"
	# Note: for COUNTER == 0, the `tmpX` is replaced with `base`
	LAYERS+="[tmp$COUNTER][stream$COUNTER] overlay=shortest=1:x=$(($COUNTER%$TILE_COLS*$TILE_SIDE)):y=$(($COUNTER/$TILE_COLS*$TILE_SIDE))"

	let COUNTER+=1
done < $FILE

# Undo the last increment
let COUNTER-=1

# Now that we have the total count of videos, calculate video size
TILE_ROWS=$(($COUNTER/$TILE_COLS+1))
OUT_WIDTH=$(($TILE_COLS*$TILE_SIDE))
OUT_HEIGHT=$(($TILE_ROWS*$TILE_SIDE))

# Create base (null source) and black color sources
SOURCES="nullsrc=size=$(($OUT_WIDTH))x$OUT_HEIGHT [base]; color=c=black, scale=$(($OUT_WIDTH))x$OUT_HEIGHT [black]; $SOURCES"

# Apply black color source on top of the base null source
LAYERS="[base][black] overlay=shortest=1 [tmp0]; $LAYERS"

# Combine intro a filter graph
FILTER_GRAPH="\"$SOURCES $LAYERS\""


# Run ffmpeg command to generate mosaic
eval ffmpeg $INPUTS -filter_complex $FILTER_GRAPH -c:v libx264 -preset fast -crf 18 output.mp4