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• How to add escape characters to a filename to be consumed later by a shell command ?

  9 mars 2023, par nhershy

  I am trying to find out which of my video files are corrupted. I loop through a directory, grab each video file, and check if it is corrupt/healthy. If the filename has no spaces nor special characters, it will work. Unfortunately, many of my files have spaces or parenthesis in the name, and this causes my shell command ffmpeg within my python script to fail. How can I retrieve the filenames in abs_file_path with the escape characters preceding the special characters ?

  


  Example filename : Movie Name (1080p)

  


  Goal : Movie\ Name\ \(1080p\)

  


  for filename in os.listdir(directory):
    if filename.endswith(tuple(VIDEO_EXTENSIONS)):
        print(f'PROCESSING: {filename}...')

        abs_file_path = os.path.join(directory, filename)

        proc = subprocess.Popen(f'./ffmpeg -v error -i {abs_file_path} -f null - 2>&1', shell=True, stdout=subprocess.PIPE)
        output = proc.communicate()[0]

        row = ''
        if not output:
            # Healthy
            print("\033[92m{0}\033[00m".format("HEALTHY -> {}".format(filename)), end='\n')  # red
            row = [filename, 0]
        else:
            # Corrupt
            print("\033[31m{0}\033[00m".format("CORRUPTED -> {}".format(filename)), end='\n')  # red
            row = [filename, 1]

        results_file_writer.writerow(row)
        results_file.flush()

results_file.flush()
results_file.close()


  


• ffmpeg - escaping special characters

  21 février 2023, par Riz

  I want to record screen using ffmpeg. Here is a simple command which I use and works fine

  


  ffmpeg -f dshow -i audio="Microphone Array (Full HD 1080P PC Camera Audio)" -f gdigrab -offset_x 0 -offset_y 0 -video_size 500x500 -framerate 30 -i desktop -pix_fmt yuv420p -vcodec libx264 -crf 28 -preset ultrafast -tune zerolatency  -movflags +faststart  "recording.mp4"


  


  But I have another USB mic (Microphone 1:2 (USB PnP Sound Device)), which has a colon ( :) in its name. When I use it for recording, it gives error

  


  [dshow @ 0000028f718db740] Malformed dshow input string.
audio=Microphone 1:2 (USB PnP Sound Device): I/O error


  


  I have tried to escape colon sign with & \ but still get same error. How to fix this ?

  


• Best logical formula to determine perceptual / "experienced" quality of a video, given resolution / fps and bitrate ?

  20 mars 2023, par JamesK

  I am looking for a formula that can provide me with a relatively decent approximation of a Video's playback quality that can be calculated based off of four metrics : width, height, fps, and bitrate (bits/sec). Alternatively, I can also use FFMPEG or similar tools to calculate a Video's playback quality, if any of those tools provide something like what I am looking for here.

  


  An example of what a Video might look like in my problem is as follows :

  


  interface Video {
  /** The width of the Video (in pixels). */
  width: number
  /** The height of the Video (in pixels). */
  height: number
  /** The frame rate of the Video (frames per second). */
  fps: number
  /** The bitrate of the video, in bits per second (e.g. 5_000_000 = 5Mbit/sec) */
  bitrate: number
}


  


  I came up with the following function to compute the average amount of bits available for any given pixel per second :

  


  const computeVideoQualityScalar = (video: Video): number => {
  // The amount of pixels pushed to the display, per frame.
  const pixelsPerFrame = video.width * video.height
  
  // The amount of pixels pushed to the display, per second.
  const pixelsPerSecond = pixelsPerFrame * video.fps
  
  // The average amount of bits used by each pixel, each second,
  // to convey all data relevant to that pixel (e.g. color data, etc)
  const bitsPerPixelPerSecond = video.bitrate / pixelsPerSecond
  
  return bitsPerPixelPerSecond
}


  


  While my formula does do a good job of providing a more-or-less "standardized" assessment of mathematical quality for any given video, it falls short when I try to use it to compare videos of different resolutions to one another. For example, a 1080p60fps video with a bitrate of 10Mbit/sec has a greater visual fidelity (at least, subjectively speaking, to my eyes) than a 720p30fps video with a bitrate of 9Mbit/sec, but my formula would score the 720p30fps video significantly higher than the 1080p60fps video because the 720p video has more bits available per pixel per second than the 1080p video.

  


  I am struggling to come up with ideas as to how to either come up with a different way to calculate the "subjective video quality" for a given video, or extend upon my existing idea here.