#------------------------------------------------------------------------------
#Ref: karobben.github.io/2021/04/10/Python/opencv-v-paste
#Code adapted to add videos up/down and side. The second to fourth videos are
# scaled to width of first video. FPS of all videos changed to that of first.
# Arrangement of videos is 
#   First    Second
#   Third    Fourth
# Code was tested on a video of resolution 1280x720 and the resultant video 
# having size 2560x1440 could be opened without any error on Ubuntu LTS 22.0, 
# 15.4" monitor (1366x768) of resolution 100 DPI.
#------------------------------------------------------------------------------
import cv2
import numpy as np
#Read the input videos and specify name of the output video
Vid1 = "v1.mp4"
Vid2 = "v2.mp4"
Vid3 = "v1.mp4"
Out = "vid-3-in-2x2.mp4"

cap1 = cv2.VideoCapture(Vid1) 
cap2 = cv2.VideoCapture(Vid2)
cap3 = cv2.VideoCapture(Vid3) 
Window = None  #or '1920x1080' or '1280x720' - check Aspect Ratio of input

#Get the fps and the size of the Video one
fps_c1 = cap1.get(cv2.CAP_PROP_FPS)
h1 = cap1.get(cv2.CAP_PROP_FRAME_HEIGHT)
w1 = cap1.get(cv2.CAP_PROP_FRAME_WIDTH)

def frameConnect(f1, f2, f3, img4, h1, w1):
	f2 = cv2.resize(f2, (int(w1), int(h1)), interpolation = cv2.INTER_AREA)
	f3 = cv2.resize(f3, (int(w1), int(h1)), interpolation = cv2.INTER_AREA)
	BG = cv2.resize(f1, (int(w1*2), int(2*h1)), interpolation=cv2.INTER_AREA)
	BG[0:int(h1),0:int(w1)] = f1
	BG[0:int(h1),int(w1):int(w1*2)] = f2
	BG[int(h1):int(h1*2),0:int(w1)] = f3
	BG[int(h1):int(h1*2),int(w1):int(w1*2)] = img4
	return (BG)

# Set argument for Video Output
fps = fps_c1

if Window == None:
	size = (int(w1*2), int(h1*2))
else:
	size = (int(Window.split("x")[0]), int(Window.split("x")[1]))

fourcc = cv2.VideoWriter_fourcc('m','p','4','v')
videowriter = cv2.VideoWriter(Out,fourcc,fps,size)

img4 = np.ones((int(h1),int(w1),3), np.uint8) * 255

while (True):
	ret,f1=cap1.read()
	ret,f2=cap2.read()
	ret,f3=cap3.read()
	#Prevent resize of a Null image, which is the LAST frame of the video
	if ret == True:
		img = frameConnect(f1, f2, f3, img4, h1, w1)
		img = cv2.resize(img, size, interpolation = cv2.INTER_AREA)
		videowriter.write(img)
	else:
		break

cap1.release()
cap2.release()
cap3.release()
videowriter.release()
cv2.destroyAllWindows()