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• Evolution #2941 (Fermé) : RSS enclosure et media:content

  1er mars 2013, par marcimat -

  Fermé par

  r20221 et report r20225

  http://zone.spip.org/trac/spip-zone/changeset/70316 et report http://zone.spip.org/trac/spip-zone/changeset/70317 Merci :)

• fftools/ffmpeg : store stream media type in OutputStream

  11 avril 2023, par Anton Khirnov

  fftools/ffmpeg : store stream media type in OutputStream
  Reduces access to a deeply nested muxer property
  
  OutputStream.st->codecpar->codec_type for this fundamental and immutable
  
  stream property.
  Besides making the code shorter, this will allow making the AVStream
  
  (OutputStream.st) private to the muxer in the future.
  

  • [DH] fftools/ffmpeg.c
  • [DH] fftools/ffmpeg.h
  • [DH] fftools/ffmpeg_mux.c
  • [DH] fftools/ffmpeg_mux_init.c

• Python OpenCV VideoCapture Color Differs from ffmpeg and Other Media Players

  17 avril 2024, par cliffsu

  I’m working on video processing in Python and have noticed a slight color difference when using cv2.VideoCapture to read videos compared to other media players.

  


  

  


  I then attempted to read the video frames directly using ffmpeg, and despite using the ffmpeg backend in OpenCV, there are still differences between OpenCV’s and ffmpeg’s output. The frames read by ffmpeg match those from other media players.

  


  

  


  Below are the videos I’m using for testing :

  


  test3.webm

  


  test.avi

  


  Here is my code :

  


  import cv2
import numpy as np
import subprocess

def read_frames(path, res):
    """Read numpy arrays of video frames. Path is the file path
       and res is the resolution as a tuple."""
    args = [
        "ffmpeg",
        "-i",
        path,
        "-f",
        "image2pipe",
        "-pix_fmt",
        "rgb24",
        "-vcodec",
        "rawvideo",
        "-",
    ]

    pipe = subprocess.Popen(
        args,
        stdout=subprocess.PIPE,
        stderr=subprocess.DEVNULL,
        bufsize=res[0] * res[1] * 3,
    )

    while pipe.poll() is None:
        frame = pipe.stdout.read(res[0] * res[1] * 3)
        if len(frame) > 0:
            array = np.frombuffer(frame, dtype="uint8")
            break

    pipe.stdout.close()
    pipe.wait()
    array = array.reshape((res[1], res[0], 3))
    array = cv2.cvtColor(array, cv2.COLOR_RGB2BGR)
    return array

ORIGINAL_VIDEO = 'test3.webm'

array = read_frames(ORIGINAL_VIDEO, (1280, 720))

cap = cv2.VideoCapture(ORIGINAL_VIDEO, cv2.CAP_FFMPEG)
while cap.isOpened():
    ret, frame = cap.read()
    if not ret:
        break
    print(frame.shape)
    cv2.imshow("Opencv Read", frame)
    cv2.imshow("FFmpeg Direct Read", array)
    cv2.waitKeyEx()
    cv2.waitKeyEx()
    break
cap.release()


  


  I’ve attempted to use different media players to compare cv2.VideoCapture and ffmpeg’s frame reading, to confirm that the issue lies with opencv. I’m looking to determine whether it’s a bug in OpenCV or if there are issues in my code.

  


  EDIT :

  


  Just use the following code to check the difference between opencv read and ffmpeg read.

  


  cv2.imshow('test', cv2.absdiff(array, frame)*10)
cv2.waitKey(0)


  


  Here is the result :