hello i’m testing opencv with video. I can normally capture image from camera but i think there is a codec issue cause when i save the stream from camera or when i try to load a video from a file it doesn’t work

i’m using mac os Catalina 10.15.7, python 3.8.5, ffmpeg 4.3.1

this is my code

import cv2
import numpy as np 
vid = cv2.VideoCapture('trailer.mp4')
while(vid.isOpened()):
    ret, frame = vid.read()
    cv2.imshow('frame',frame)
    k = cv2.waitKey(25)
    if k == 27:
        break
vid.release()
cv2.destroyAllWindows()
The error i get is OpenCV: Couldn’t read video stream from file
what’s the problem?? is it a codec error?
that precise string does not occur within OpenCV (edit: I was mistaken. it’s related to AVFoundation, MacOS). nor can it apply to your code. your code reads from a camera device, not a file. your code writes to a file, it doesn’t read.
please be precise and complete in the error messages you get.
ok i’m a damn stupid… i forgot I had moved the path! when i used ur code it gave me false so i realized it…
Thanks a lot…
considering im there, why does code saved from cam won’t open even if the file is saved?
VideoWriter needs .release() at the end to finalize the file
the container type (mp4) and codec (XVID??) you specified aren’t possible
opencv seems to pick the avfoundation backend. it may not know what XVID is. try “MP42”, “AVC1”, “HVC1”/“HEVC”, …
cam = cv2.VideoCapture(0) #get the first webcam
####defining the codec and creating the VideoWriter Obj
fourcc = cv2.VideoWriter_fourcc(*'XVID')
out=cv2.VideoWriter('./assets/output.avi',fourcc,20.0,(1280,960))
while(cam.isOpened()):
    ret, frame = cam.read()
    if ret==True:
        out.write(frame)
        cv2.imshow('frame',frame)
        if cv2.waitKey(1) & 0xFF == ord('q'):
            break
    else:
        break
cam.release()
out.release()
cv2.destroyAllWindows()
this is the code (the one i posted by mistake) i can change XVID with MP42 AVC1, but what would be the file extension in the name? is there a way to check which is the right codec? i tried to check the list of codec with ffmpeg -encoders
              
if you want to be sure to get ffmpeg, you need to pass cv2.CAP_FFMPEG as apiPreference argument to the VideoWriter constructor
if you can get ffmpeg, I’d recommend making “.mkv” files.