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• Better Image Quality with Python OpenCV

  6 avril 2023, par bozolino

  I use OpenCV to capture webcam video as frames to a list variable, then write that list to disk both as image sequence and as a video file. The image quality is fine. But the video is horribly compressed, with a bitrate of less than 4mbit, sometimes even less than 3mbit.

  


  I've spent days and nights on Google finding solutions, tried many fourccs and other wrappers like WriteGear and ffmpeg-python, but to no avail.

  


  Can anyone please tell me how I

  


  a) specify the bitrate for my H.264 file, and

  


  b) choose a lossless compression codec ?

  


  (Python 3.10 on MacOS MacBook Pro M1 / MacOS 13.0.1)

  


  # ::::: import libraries and set variables

import cv2, time, os, shutil, datetime as dt
frames = []
frame_dimensions_known = False

# ::::: define file and folder names

output_folder_name = "output"
frame_folder_name = "frames"
video_file_name = "video.mp4"
frame_file_name = "frame_x.jpg"

# ::::: create output folders and paths

path_script = os.path.abspath(os.path.dirname(__file__))
path_output = os.path.join(path_script,output_folder_name)
if not os.path.exists(path_output):
    os.mkdir(path_output)
    path_session_fold
path_session_folder  = os.path.join(
    path_script,
    output_folder_name,
    dt.datetime.now().strftime("%y%m%d_%H%M%S"))
os.mkdir(path_session_folder)
path_video =  os.path.join(path_session_folder,video_file_name)
path_frames = os.path.join(path_session_folder,frame_folder_name)
os.mkdir(path_frames)


# ::::: open webcam stream

vcap = cv2.VideoCapture(0)
start_time = (time.time() * 1000)
if vcap.isOpened() is False:
    print("[Exiting]: Error accessing webcam stream.")
    exit(0)

# ::::: read frames

while True:
    _grabbed, _frame = vcap.read()
    if _grabbed is False:
        print('[Exiting] No more frames to read')
        exit(0)

    # ::::: get frame dimensions on first read
    if not frame_dimensions_known:
        height, width, channels = _frame.shape
        frame_dimensions_known = True

    # ::::: append frame to list
    frames.append(_frame)

    # ::::: process frames
    pass

    # ::::: display frame
    cv2.imshow("cam", _frame)
    if cv2.waitKey(1) == ord("q"):
        break

# ::::: close webcam stream

vcap.release()
cv2.destroyAllWindows()

# ::::: calculate frame rate

stop_time = (time.time() * 1000)
total_seconds = (stop_time - start_time) / 1000
fps = len(frames) / total_seconds

# ::::: open video writer

fourcc = cv2.VideoWriter_fourcc(*'mp4v')
video_writer = cv2.VideoWriter(
    path_video,
    fourcc,
    fps,
    (width, height)
)

# ::::: write frames to disk as files and video

frame_number = 0
for frame in frames:

    # ::::: write video

    video_writer.write(frame)  # Write out frame to video

    # ::::: construct image file path

    frame_number = frame_number + 1
    frame_number_file = str(frame_number).zfill(4)
    frame_name = frame_file_name.replace('x',frame_number_file)
    frame_path = os.path.join(path_frames,frame_name)

    # ::::: write image

    cv2.imwrite(
        frame_path,
        frame,
        [cv2.IMWRITE_JPEG_QUALITY, 100]
    )

# ::::: clean up

video_writer.release
print (f"Written {frame_number} frames at {fps} FPS.")



  


• Screenshot of video file in Electron Angular project without ffmpeg

  15 juin 2022, par Gary Klasen

  Within my Electron Angular project, I want to preview a video file which is stored locally on Windows / MacOS within a frame, like this :

  


  

  


  On the left side, currently, there is a placeholder image. But i want to have a snapshot out of the video, it is not important at which position of the video this is taken.

  


  Our attempt at the moment is to use fluent-ffmpeg library from npm :

  


  var ffmpeg = require('fluent-ffmpeg');

let command = new ffmpeg({source: "MY_VIDEO_PATH"}).inputOptions('-protocol_whitelist file,http,https,tcp,tls,crypto')

command.takeScreenshots({
    count: 1,
    timemarks: ['5%'],
    filename: "MY_FILENAME"
}, "DESTINATION_FOLDER_PATH_FOR_THUMB");


  


  It takes the screen after 5% of the video would have been played. However, this requires ffmpeg executable to be present, which actually costs more space for the application as we want to use.

  


  So : Can i pick out a screenshot out of a video file without using additional executables like ffmpeg ? If there are some suitable npm libaries, this would be also fine, as they are a lot smaller.

  


• ffmpeg is failing to load shared libraries after a ./configure with a prefix inside a conda environment

  30 janvier 2024, par user3133806

  I am using conda and building ffmpeg from source within that environment.

  


  I ran the following commands :

  


  conda create --name my_conda_env
conda activate my_conda_env
# Now I am in the conda environment
# $CONDA_PREFIX is /home/myuser/.conda/envs/my_conda_env/bin/ffmpeg

# Checkout ffmpeg code
# git checkout ...

./configure --prefix=$CONDA_PREFIX --enable-shared --disable-static && make distclean && make -j 100 && make install

# The above command does install the newly built ffmpeg into:
# /home/myuser/.conda/envs/my_conda_env/bin/ffmpeg

# However it fails to execute:
ffmpeg
ffmpeg: error while loading shared libraries: libavdevice.so.58: cannot open shared object file: No such file or directory

# When I add the conda lib path to LD_LIBRARY_PATH it works:
LD_LIBRARY_PATH=$CONDA_PREFIX/lib:$LD_LIBRARY_PATH ffmpeg
ffmpeg version n4.2.9-4-gd7beb0c61f Copyright (c) 2000-2023 the FFmpeg developers

# I thought ./configure with a --prefix will build a binary that will search for libraries relative to itself, but that does not appear to be the case:

strace -o /tmp/strace.out ffmpeg
tail /tmp/strace.out

openat(AT_FDCWD, "/usr/lib64/haswell/x86_64/libavdevice.so.58", O_RDONLY|O_CLOEXEC) = -1 ENOENT (No such file or directory)
newfstatat(AT_FDCWD, "/usr/lib64/haswell/x86_64", 0x7fff65f56d90, 0) = -1 ENOENT (No such file or directory)
openat(AT_FDCWD, "/usr/lib64/haswell/libavdevice.so.58", O_RDONLY|O_CLOEXEC) = -1 ENOENT (No such file or directory)
newfstatat(AT_FDCWD, "/usr/lib64/haswell", 0x7fff65f56d90, 0) = -1 ENOENT (No such file or directory)
openat(AT_FDCWD, "/usr/lib64/avx512_1/x86_64/libavdevice.so.58", O_RDONLY|O_CLOEXEC) = -1 ENOENT (No such file or directory)
newfstatat(AT_FDCWD, "/usr/lib64/avx512_1/x86_64", 0x7fff65f56d90, 0) = -1 ENOENT (No such file or directory)
openat(AT_FDCWD, "/usr/lib64/avx512_1/libavdevice.so.58", O_RDONLY|O_CLOEXEC) = -1 ENOENT (No such file or directory)
newfstatat(AT_FDCWD, "/usr/lib64/avx512_1", 0x7fff65f56d90, 0) = -1 ENOENT (No such file or directory)
openat(AT_FDCWD, "/usr/lib64/x86_64/libavdevice.so.58", O_RDONLY|O_CLOEXEC) = -1 ENOENT (No such file or directory)
newfstatat(AT_FDCWD, "/usr/lib64/x86_64", 0x7fff65f56d90, 0) = -1 ENOENT (No such file or directory)
openat(AT_FDCWD, "/usr/lib64/libavdevice.so.58", O_RDONLY|O_CLOEXEC) = -1 ENOENT (No such file or directory)
newfstatat(AT_FDCWD, "/usr/lib64", {st_mode=S_IFDIR|0555, st_size=49526, ...}, 0) = 0
writev(2, [{iov_base="ffmpeg", iov_len=6}, {iov_base=": ", iov_len=2}, {iov_base="error while loading shared libra"..., iov_len=36}, {i
ov_base=": ", iov_len=2}, {iov_base="libavdevice.so.58", iov_len=17}, {iov_base=": ", iov_len=2}, {iov_base="cannot open shared object file", iov_len=30}, {iov_base=": ", iov_len=2}, {iov_base="No such file or directory", iov_len=25}, {iov_base="\n", iov_len=1}], 10) = 
123


  


  Conda documentation says not to use LD_LIBRARY_PATH here :

  


  https://docs.conda.io/projects/conda-build/en/stable/resources/use-shared-libraries.html#shared-libraries-in-macos-and-linux

  


  How can I build ffmpeg from source in a conda environment and have the binary find the .so file relative to itself ?