gistfile1.sh

# First we will create the splash video part in a lossless format
SPLASH_TEMP=$(mktemp --suffix=.mp4)
$FFMPEG -loop 1 -i "$INPUT_SPLASH" -t $SPLASH_LENGTH -c:v libx264 -pix_fmt yuv420p -preset ultrafast -qp 0 -y "$SPLASH_TEMP"

# Then create the final timelapse
$FFMPEG \
    -i "$SPLASH_TEMP" \
    -i "$INPUT_VIDEO" \
    -i "$INPUT_AUDIO" \
    -filter_complex "[1:v]setpts=$PTS*PTS [tl]; [0:v] [tl] concat=n=2:v=1:a=0 [v]" \
    -map '[v]' -map 2:0 \
    -codec:v libx264 -pix_fmt yuv420p -profile:v high -preset slow -b:v 4m -maxrate 4m -bufsize 8m -threads 0  \
    -codec:a libvo_aacenc -b:a 192k -ac 2 -ar 48000 \
    -shortest \
    -y \
    "$OUTPUT_FILE"