#Python script to convert PNG files to a MOVIE (MP4) file.  Make sure that PNG
#files are of nearly equal size. Alternatively, you can specify size of GIF file
#[H x W] = Height x Width.  Apply argument -s to scale [rescale] the images.  To
#disable scaling, set n < 0 in case you are code is run from command line.
#-------------------------------------------------------------------------------
import cv2
import os, sys
from PIL import Image
import glob

imgFolder = "Images"
vidName = "Video.mp4"
#Specify size of the video if different from image size: 848x480, 1280x720
W = 640
H = 360
#Define number of frames (images) per second. A frame rate refers to the number 
#of individual frames or images that are displayed/second of film or TV display.
#Slow motion effects are created by recording hundreds of frames per second and 
#then playing them back at slower rate.  An example would be a bullet shattering 
#a light bulb. It may only take a fraction of a second but if the camera records
#the light bulb a 500 [frame/second]. When plays back at 25 FPS, this movie on 
#screen will take [500/25 = ] 20 times as long. If you shoot the bullet travel  
#for 0.1 [s] at 500 FPS and then play it back at 25 FPS it will take 0.1x500/25
#= 2 [s] to watch the video even though the scene only took 0.1 [s] to record.
nfs = 0.5

#Specify toggle variable to scale the images
n = 1

#images = [img for img in os.listdir(imagFolder) if img.endswith(".png")]
#glob.glob(Pathname) fetches all file with extension PNG in that folder
images = glob.glob(os.path.join(imgFolder, "*.png"))
images.sort()

width, height = Image.open(images[0]).size
size = (width, height)
codec = cv2.VideoWriter_fourcc(*'mp4v') #DIVX, DIVD
if (len(sys.argv) < 2 and n > 0):
    video = cv2.VideoWriter(vidName, codec, nfs, (W, H))
else:
    video = cv2.VideoWriter(vidName, codec, nfs, size)

#Do not open images in 'Image' as well as 'CV2', else following error occurs
#<built-in function imread> returned NULL without setting an error
for img in images:
    #In case images are of different size, resize them to user specified values
    if (len(sys.argv) < 2 and n > 0):
        newImg = cv2.imread(img)
        newImg = cv2.resize(newImg, (W, H))
        video.write(newImg)
    else:
        video.write(img)

video.release()
cv2.destroyAllWindows()