Develop Reference

How to extract all the frames from a video?

Hey so I wanted to know how I can extract all frames from a vide using MoviePy
Currently I am doing it in open-cv which is really really slow. My current code :-
vidObj = cv2.VideoCapture("./video.mp4")
count = 0
flag = 1
while flag:
flag, image = vidObj.read()
try:
cv2.imwrite(f"./images/frame{count}.jpg", image)
except:
break
count += 1
Can someone tell me how to achieve the same in MoviePy please?

You can use the write_images_sequence() method.
%05d represents a 5 digit frame index.
from moviepy.editor import VideoFileClip
video = VideoFileClip('video.mp4')
video.write_images_sequence('frame%05d.png', logger='bar')

Parse video at lower frame rate

I currently am working on a project where I need to parse a video and pass it through several models. The videos come in at 60fps. I do not need to run every frame through the models. I am running into some issue when trying to skip the unneeded frames. I have tried two methods which are both fairly slow.
Method 1 code snippet:
The issue here is that I am still reading every frame of the video. Only every 4th frames is run through my model.
cap = cv2.VideoCapture(self.video)
while cap.isOpened():
success, frame = cap.read()
if count % 4 !=0:
count += 1
continue
if success:
''Run frame through models''
else:
break
Method 2 code snippet:
This method is slower. I am trying to avoid reading unnecessary frames in this case.
cap = cv2.VideoCapture(video)
count=0
while True:
if count % 4 != 0:
cap.set(cv2.CV_CAP_PROP_POS_FRAMES, count*15)
count+=1
success, frame = cap.read()
Any advice on how to achieve this in the most efficient way would be greatly appreciated.

Getting and setting frames by changing CV_CAP_PROP_POS_FRAMES is not accurate (and slow) due to how video compression works: by using keyframes.
It might help to not use the read() function at all. Instead use grab() and only retrieve() the needed frames. From the documentation: The (read) methods/functions combine VideoCapture::grab() and VideoCapture::retrieve() in one call.
grab() gets the frame data, and retrieve() decodes it (the computationally heavy part). What you might want to do is only grab frames you want to skip but not retrieve them.
Depending on your system and opencv build, you could also have ffmpeg decode video using hardware acceleration.

As I get it you are trying to process every fourth frame. You are using the condition:
if count % 4 != 0
which is triggered 3 out of 4 frames instead (you are processing frames 1, 2, 3, 5, 6, 7 etc)! Use the opposite:
if count % 4 == 0
Also although code snippets the two method does not seem to process the same frames. Although in both cases your counter seems to increase by 1 in each frame you actually point to the 15xframe of that counter in the second case (cap.set(cv2.CV_CAP_PROP_POS_FRAMES, count*15).
Some comments on your code also (maybe I misunderstood something):
Case 1:
while cap.isOpened():
success, frame = cap.read()
if count % 4 !=0:
count += 1
continue
here you seem to count only some frames (3 out of 4 as mentioned) since frames which are multiples of 4 are skipped: condition count % 4 !=0 is not met in that case and your counter is not updated although you read a frame. So, you have an inaccurate counter here. It's not shown how and where do you process you frames to judge that part though.
Case 2:
while True:
if count % 4 != 0:
cap.set(cv2.CV_CAP_PROP_POS_FRAMES, count*15)
count+=1
success, frame = cap.read()
here you read frames only if condition is met so in this code snippet you don't actually read any frame since frame 0 does not trigger the condition! If you update the counter outside the if scope it's not clear here. But if you do you should also read a frame there. Anyway more code should be revealed to tell.
As a general advice you should update the counter everytime you read a frame.

Instead putting a threshold on number of frames, which would make opencv process ALL the frames (which you rightly pointed out, slows the video processing), it's better to use CAP_PROP_POS_MSEC link and offload that processing to cv2. By using this option you can configure cv2 to sample 1 frame every nth Millisecond. So setting subsample_rate=1000 in vidcap.set(cv2.CAP_PROP_POS_MSEC, (frame_count * subsample_rate)) would sample 1 frame every 1 second (as 1000 milliseconds equals 1 second). Hopefully this improves your video processing speed.
def extractImagesFromVideo(path_in, subsample_rate, path_out, saveImage, resize=(), debug=False):
vidcap = cv2.VideoCapture(path_in)
if not vidcap.isOpened():
raise IOError
if debug:
length = int(vidcap.get(cv2.cv2.CAP_PROP_FRAME_COUNT))
width = int(vidcap.get(cv2.cv2.CAP_PROP_FRAME_WIDTH))
height = int(vidcap.get(cv2.cv2.CAP_PROP_FRAME_HEIGHT))
fps = vidcap.get(cv2.cv2.CAP_PROP_FPS)
print 'Length: %.2f | Width: %.2f | Height: %.2f | Fps: %.2f' % (length, width, height, fps)
success, image = vidcap.read() #extract first frame.
frame_count = 0
while success:
vidcap.set(cv2.CAP_PROP_POS_MSEC, (frame_count*subsample_rate))
success, image = vidcap.read()
if saveImage and np.any(image):
cv2.imwrite(os.path.join(path_out, "%s_%d.png" % (frame_count)), image)
frame_count = frame_count + 1
return frame_count

How to read the first frame of video using OpenCV in python?

Here is some code I am using which should succeed in returning the first frame of a video. The relevant bits here I think are lines 2:5 and the second to last one where count=2.
def define_bounds(video_file, threshold_value, index_value):
vidcap = cv2.VideoCapture(video_file)
count=0
while count <1:
success,color_img = vidcap.read()
blkwht_img = np.asarray(Image.fromarray(color_img).convert('L'))[index_value]
retval, final_img = cv2.threshold(blkwht_img, threshold_value, 200, cv2.ADAPTIVE_THRESH_GAUSSIAN_C)
for pixel_row in range(139,-1,-1):
if np.median(final_img[pixel_row,:]) <10:
silenced = pixel_row - 2
upmotion = pixel_row - 16
destination = pixel_row - 44
downmotion = pixel_row - 31
break
count=2
return silenced, upmotion, destination, downmotion
I do know for a fact that vidcap.read() succeeds in reading frames from the first to the last (I have other code I use to determine this, where it just exports all frames from first to last).
But this code above fails in reading the first frame... it reads SOME frame but I don't know which. It's not the first, second or last as the output of the function does not match when I manually input the first, second and last frames.
Is there something stupidly wrong in my code? Also: am I using break correctly? I'm still new to this. Thanks!

How to verify that two images are exactly identical?

I am writing an opencv program where I track position of an object by use of a usb camera. To make sure I get as high frame rate as possible with the camera I am using I made a threaded process that read the images from the camera. The image processing is done in another loop which also writes the object position to the file.
Now I want a way to avoid processing the same frame multiple times. So I thought I could compare the image just processed with that available from the the video stream thread.
First I tried to use if frame1 == frame2, but got error message that "the truth value of an array with more than one element is ambiguous. Use a.any() or a.all()."
After some googling I found cv2.compare and the flag CMP_EQ. Made a sample code, and made it work in some way. However, my question is. How could this be done in an easier or better way?
import cv2
cv2.namedWindow('image1', cv2.WINDOW_NORMAL)
cv2.namedWindow('image2', cv2.WINDOW_NORMAL)
frame1 = cv2.imread("sample1.png")
frame2 = frame1
frame3 = cv2.imread("sample2.png")
compare1 = cv2.compare(frame1,frame2,0)
compare2 = cv2.compare(frame1,frame3,0)
cv2.imshow('image1', compare1)
cv2.imshow('image2', compare2)
if compare1.all():
print "equal"
else:
print "not equal"
if compare2.all():
print "equal"
else:
print "not equal"
cv2.waitKey(0)
cv2.destroyAllWindows()

open("image1.jpg","rb").read() == open("image2.jpg","rb").read()
should tell you if they are exactly the same ...

I was doing something close to what you are doing; I was trying to get the difference. I used the subtract function. It may help you.
UPDATE:
import cv2
import numpy as np
a = cv2.imread("sample1.png")
b = cv2.imread("sample2.png")
difference = cv2.subtract(a, b)
result = not np.any(difference)
if result is True:
print "Pictures are the same"
else:
cv2.imwrite("ed.jpg", difference )
print "Pictures are different, the difference is stored as ed.jpg"

How about giving your Images an index?
Pseudocode:
class Frame
{
cvImage img;
uint idx;
}
Than simply check if the current index is greater than the last one you processed.
It is simple and definitely faster than any image processing based approach.

You can compare the size of two image files as the first level of check for reduced computational complexity. With compression, it is highly unlikely for two different image files to have the same size to the accuracy of the number of bytes. With equal file size, you can then compare the image contents.

You should try something like this.
import cv2
import numpy as np
original = cv2.imread("rpi1.jpg")
duplicate = cv2.imread("rpi2.jpg")
if original.shape == duplicate.shape:
print("The images have same size and channels")
difference = cv2.subtract(original, duplicate)
b, g, r = cv2.split(difference)
if cv2.countNonZero(b) == 0 and cv2.countNonZero(g) == 0 and
cv2.countNonZero(r) == 0:
print("The images are completely Equal")
else:
print("images are different")

More problems extracting frames from GIFs

Following my previous question (Gifs opened with python have broken frames) I now have code that works sometimes.
For example, this code
from PIL import Image
img = Image.open('pigs.gif')
counter = 0
collection = []
current = img.convert('RGBA')
while True:
try:
current.save('original%d.png' % counter, 'PNG')
img.seek(img.tell()+1)
current = Image.alpha_composite(current, img.convert('RGBA'))
counter += 1
except EOFError:
break
…works on most GIFs perfectly, but on others it produces weird results. For example, when applied to this 2-frame GIF:
It produces these two frames:
The first one is ok, the second one not so much.
What now?

Sounds like you want to do this:
while True:
try:
current.save('original%d.gif' % counter)
img.seek(img.tell()+1)
current = img.convert('RGBA')
counter += 1
except EOFError:
break

try Wand (Wand is a ctypes-based simple ImageMagick binding for Python.)
from wand.image import Image
def extract_frames(gif_file):
with Image(filename=gif_file) as gif:
for i, single_img in enumerate(gif.sequence):
with Image(image=single_img) as frame:
frame.format = 'PNG'
frame.save(filename='frame-%d.png' % i)
extract_frames('test.gif')
frame-0.png
frame-1.png