#This Python + OvenCV code adds a string to a video in Typewriter style. That
#is 1 character at a time.  The user can specifiy the start time and the speed
#at which text should be added to the video.
#------------------------------------------------------------------------------
import cv2, sys

#Provide input video and name of the output video
inVidName = 'in.mp4'
outVidName = 'out.mp4'

#Create a video capture object and read from input video file. If the input is
#the camera, pass 0 instead of the video file name
cap = cv2.VideoCapture(inVidName)

#Check if camera opened sucessfully
if (cap.isOpened() == False):
	print("Error Opening Video Stream of the File, exiting")
	sys.exit()
	
#Specifiy start time after which text should get added
tS = 0.5

#Specify duration in seconds between two characters to be added to the video
tTxt = 0.25

#Spcify the string (text) to be added
txt = "Rotating Wheel"

#Specify the font colour in BGR format
fc = (0, 0, 255)

#Speify the font scale: this value scales base size of the text 
fs = 1

#Specify font type
fo = cv2.FONT_HERSHEY_SIMPLEX

#Specify font thickness
ft = 1

#Specify width, height location factor: x,y value at which text start appearing
xW = 0.10
xH = 0.80

# -----------------------No Futher Inputs from User is Needed------------------
#Get frame height and width of the video and calculate x,y coordinate of text
FW = int(cap.get(cv2.CAP_PROP_FRAME_WIDTH))
FH = int(cap.get(cv2.CAP_PROP_FRAME_HEIGHT))
x = int(FW * xW)
y = int(FH * xH)

#Get total number of frames in the video and duration of the video
fps = int(cap.get(cv2.CAP_PROP_FPS))
nframe = int(cap.get(cv2.CAP_PROP_FRAME_COUNT))
duration = nframe/fps
minutes = int(duration/60)
seconds = duration % 60

#Check that width of the text does not exceed width of the video frame
nT = len(txt)
txtWidth, _ = cv2.getTextSize(txt, fo, fs, ft)
if (x + txtWidth[0]) >= FW:
	print("\n All text cannot be printed in the width of the video, exiting")
	print("\n Width of the video: ", FW)
	print("\n Width of the text excluding start location: ", txtWidth[0])
	print("\n Excess width in pixels: ", x + txtWidth[0] - FW, "\n")
	sys.exit()
	
#Check if the time taken to add the video does not exceed video duration
tTxtDura = nT * tTxt
if (tS + tTxtDura) > duration:
	print("\n Text cannot be added before end of video, exiting")
	sys.exit()
	
#Get frame numbers at which text should start to appear and stops appearing
nS = int(tS * fps)
nE = int(nS + nT * (fps * tTxt))

#Create a video writter object and start the loop to add 1 character at a time
codec = cv2.VideoWriter_fourcc(*'mp4v')
video = cv2.VideoWriter(outVidName, codec, fps, (FW, FH))

#Start the counter for frames in the video
i = 1

#Start the counter for number of characters in the text
j = 0

#Read the video till last frame, add text based on specified conditions
while (cap.isOpened() == True):
	#Capture each frame of the video
	ret, frm = cap.read()
	if (ret == True):
		#Write the frame as it is if falls before start of text addition
		if (i < nS):
			video.write(frm)
			
		#Write the text after start time of the text addition
		if (i > nS and i < nE):
			#Calculate number of frames between two characters
			m = int((i - nS) / (fps * tTxt))
			j = m
			if (j <= nT):
				for k in range(j+1):
					cv2.putText(frm,txt[0:k],(x,y),fo,fs,fc,ft)
				j = j + 1
				video.write(frm)
		
		#Write the entire text once all text added with Typewritter Effect
		if (i > nE):
			cv2.putText(frm,txt[0:nT],(x,y),fo,fs,fc,ft,cv2.LINE_4)
			video.write(frm)
		i = i + 1
	#Break the loop once end of video is reached
	else:
		break
		
#Release the video capture and writer objects and close all frames
cap.release()
video.release()
cv2.destroyAllWindows()