How to process video with OpenCV2 in Google Cloud function? - opencv

Question

Starting point:
There is video called myVideo.mp4 in a folder (/1_original_videos) in a Bucket called myBucket in Google Cloud Storage.
myBucket
-->/1_original_video
-->myVideo.mp4
Goal:
The goal is to take this video, split it into chunks in a Cloud Function myCloudFunction and save the chunks in a subfolder called chunks in myBucket. The part of dividing into chunks is not a problem. The problem is reading the video.
myCloudFunction must be triggered with an HTTP trigger.
_______________
myVideo.mp4 ---->|myCloudFunction|----> chunk0.mp4, chunk1.mp4, chunk2.mp4, ... , chunkN-1.mp4
‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾
^
|
|
|
HTTP trigger
If the video were on my local computer, in order to read it, the following would be enough:
import cv2
cap = cv2.VideoCapture("/some/path/in/my/local/computer/myVideo.mp4")
Attempts:
Path with authenticated URL:
import cv2
cap = cv2.VideoCapture("https://storage.cloud.google.com/myBucket/1_original_videos/myVideo.mp4")
When testing this approach, this is the resulting message (see complete code below):
"File Cannot be Opened"
Complete code:
import cv2
def video2chunks(request):
# Request:
REQUEST_JSON = request.get_json()
#If the HTTP contains a key called "start" (e.g. "{"start":"whatever"}"):
if REQUEST_JSON and 'start' in REQUEST_JSON:
try:
# Create VideoCapture object:
cap = cv2.VideoCapture("https://storage.cloud.google.com/myBucket/1_original_videos/myVideo.mp4")
# If no VideoCapture object is created:
if not cap.isOpened():
message = "File Cannot be Opened"
# If a Videocapture object is created, compute some of the video parameters:
else:
fps = int(cap.get(cv2.CAP_PROP_FPS))
size = (int(cap.get(cv2.CAP_PROP_FRAME_WIDTH)),int(cap.get(cv2.CAP_PROP_FRAME_HEIGHT)))
fourcc = int(cv2.VideoWriter_fourcc('X','V','I','D')) # XVID codecs
message = "Video downloaded successfully. Some params are: "
message += "FPS= " + str(fps) + " | size= " + str(size)
except Exception as e:
message = str(e)
else:
message = "You did not provide a key called start "
return message
I have been trying to find examples or a better way to do this in a Cloud Function but so far have been unsuccessful. Any alternatives would also be very much appreciated.

Answer 1

I'm not aware whether the cv2 library supports reading directly from Cloud Storage in some way. Nonetheless as Christoph points out you may download the file, process it and upload the results. The code will be essentially the same as running locally.
One thing to note is that Cloud Functions offer a temporal directory which is the way I chose to store the image. However it's important to know that any file stored there is actually consuming part of your function RAM, so the allocated function memory should be sized accordingly. Also you may notice the temp files are deleted before exiting the function, this is just a best practice in Cloud Functions.
import cv2
import os
from google.cloud import storage
def myfunc(request):
# Substitute the variables below for whatever suits your needs
# BUCKET_ID :: The bucket ID
# INPUT_IMAGE_GCS :: Path to GCS object
# OUTPUT_IMAGE_PATH :: Path to save the resulting image/video
# Read video and save to /tmp directory
bucket = storage.Client().bucket(BUCKET_ID)
blob = bucket.blob(INPUT_IMAGE_GCS)
blob.download_to_filename('/tmp/video.mp4')
# Video processing stuff
vidcap = cv2.VideoCapture('/tmp/video.mp4')
success, image = vidcap.read()
cv2.imwrite("/tmp/frame.jpg", image)
# Save results to GCS
img_blob = bucket.blob('potato/frame.jpg')
img_blob.upload_from_filename(OUTPUT_IMAGE_PATH)
# Delete tmp resources to free memory
os.remove('/tmp/video.mp4')
os.remove('/tmp/frame.jpg')
return '', 200