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• 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.

  


• How to scale watermark based on video resolution in android using FFmpeg command ?

  16 février 2023, par Ravi Sorathiya

  I want to scale the watermark size based on the given video resolution. but this cmd scales the watermark without respect to the original video.

  


  I want to scale the watermark based on the resolution of the video. if
the video is in high resolution then the watermark will adjust that accordingly. visa versa in lower resolution it will scale accordingly.

  


  please suggest me FFmpeg cmd the dynamically cmd that helps to scale the watermark based on video's resolution

  


  val cmd = arrayOf(
            "-y",
            "-i",
            sourcePath,
            "-i",
            watermarkImagePath,
            "-filter_complex",
            "[1][0]scale2ref=w=oh*mdar:h=ih*0.06[logo][video];[video][logo]overlay=${position}",
            "-map",
            "0:a",
            "-c:v",
            "libx264",
            "-crf",
            "$bitrate",
            "-preset",
            "ultrafast",
            outputLocation.path
        )


  


• ffmpeg scaled output resolution is off by 1px for non-standard inputs [duplicate]

  14 janvier 2023, par GROVER.

  I'm using the ffmpeg CLI to scale user-submitted videos :

  


  ffmpeg -i path/to/file -vf scale=1920:-2 -c:v libx264 -r 30 output.mp4


  


  The scaling works fine with standard video sizes, such as 1920×1080 and 720×480. However, once we start using videos that do not have conventional resolutions, the output begins to scale incorrectly.

  


  For example, a video that has a resolution of 3360×1882 will output to 1921×1076, when the expected resolution should theoretically be : 1920×1075.

  


  Now, obviously ffmpeg is attempting to account for that remaining .42857px on the height, but I'd prefer it just get cropped off instead (doesn't matter if it's from the top or bottom).

  


  How would I go about doing this safely for every video ?

  


  For bonus points, how do I make it swap scaling depending on if the height is greater than the width (and vice versa). For example, if the video has a ratio of 2:1, it scales using a height of 1080px instead of a width of 1920px.