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• Is there a way to apply a curve bend in ffmpeg ?

  25 mars 2020, par stevendesu

  I have four cameras each feeding me a different portion of a basketball court. Due to the slight offset of the cameras physical locations and lens distortion around the edges of the camera, I cannot simply stitch the videos together without some kind of correction.

  I’ve looked into ffmpeg’s perspective filter, as well as the lenscorrection filter. In the former case it was only able to create a trapezoid, not the curved image I want. In the latter case using negative values to k1 and k2 seemed to be heading in the right direction, but it either disorted the top and bottom of the image to the point of being nonsensical noise, or it zoomed in to the image so much that I lost important details.

  For the sample picture below, ultimately I want the midcourt line (the blue vertical line on the right side) to be vertical, and I want the mess of wires on the white desk at the bottom to remain visible and identifiable.

  Given a video which looks like the following :

  

  I wish to produce something like the following :

  

  This image was made using the "Curve Bend" filter in GIMP, but I just eye-balled it - so it’s not perfect. Ideally once I get the exact parameters the midcourt line will be perfectly vertical

  When using the lenscorrection filter, no values for k1 and k2 seemed to get the effect I want :

  Negative k1, negative k2 :

  

  Negative k1, positive k2 :

  

  Positive k1, negative k2 :

  

  Positive k1, positive k2 :

  

  In general :

  • negative / negative distorted the image beyond recognition
  • negative / positive looked alright, but the midcourt line was off the screen and it wasn’t clear if any distortion had been applied
  • positive / negative looked the best, but while the top and bottom curved in the middle of the left and right actually bulged out, leaving the midcourt line distorted
  • positive / positive was the opposite of the desired effect

• piping stderr/stdout to textfield from outside a process function

  29 octobre 2019, par NCrusher

  I’m trying to create a method to pipe stderr and stdout from a process to a text display. The example I borrowed a lot of the code from was written for the code to be INSIDE the method that was running the process.

  I’m trying to move the code to its own separate method so that I can use it on two different processes (one running ffprobe and one running ffmpeg with arguments built on some of the output from the ffprobe process) without repeating a huge, virtually identical chunk of code in each process.

  In each of the two processes, I’ve included this :

      let ffPipe = Pipe()
  
      probeTask.standardError = ffPipe
  
      probeTask.standardOutput = ffPipe
  
      getFfOutput(pipe: ffPipe)

  I figured I would run my ffprobe process, parse the output strings and use it to construct the ffmpeg arguments, then run the ffmpeg process and display the output just as a sort of "hey, the app is doing the thing, stand by !" heads-up to the user.

  My function for piping the output to the text display is as follows :

  func getFfOutput(pipe: Pipe) {
  
      let outHandle = pipe.fileHandleForReading
  
      outHandle.waitForDataInBackgroundAndNotify()
  
      var obs1 : NSObjectProtocol!
  
      obs1 = NotificationCenter.default
  
                               .addObserver(
  
          forName: NSNotification.Name.NSFileHandleDataAvailable,
  
          object: outHandle, queue: nil) {
  
  
  
              notification -> Void in
  
              let data = outHandle.availableData
  
              if data.count > 0 {
  
                  if let str = NSString(data: data, encoding: String.Encoding.utf8.rawValue) {
  
                      self.ffmpegLogOutput.string += ("\(str)")
  
                      let range = NSRange(location:self.ffmpegLogOutput.string.count,length:0)
  
                      self.ffmpegLogOutput.scrollRangeToVisible(range)
  
              }
  
              outHandle.waitForDataInBackgroundAndNotify()
  
              }
  
          else {
  
              print("EOF on stderr from process")
  
              NotificationCenter.default.removeObserver(obs1!)
  
          }
  
      }
  
  
  
      var obs2 : NSObjectProtocol!
  
      obs2 = NotificationCenter.default.addObserver(forName: Process.didTerminateNotification,
  
      object: probeTask, queue: nil) {
  
          notification -> Void in
  
          print("terminated")
  
          NotificationCenter.default.removeObserver(obs2!)
  
      }
  
  }

  And I think I’ve almost got it, until I get to the end.

  Specifically, the line that says object: probeTask, queue: nil). probeTask is specific to the ffprobe process. The ffmpeg process would be convertTask.

  I’m not sure how to write this so that it will return output for both processes. I’m not even sure the direction I’m heading in will work once applied to both, or if I’m going to have to repeat the output-to-display code.

  What is the best way to handle this ?

• avformat/flacdec : Remove useless packet

  8 octobre 2019, par Andreas Rheinhardt

  avformat/flacdec : Remove useless packet
  flac_read_timestamp() applied av_init_packet() to a packet (which
  
  initializes all fields of the packet except for data and size) and then
  
  went on to use only the data and size fields. In other words : Said
  
  packet can be removed and replaced by an uint8_t * and an int.
  Signed-off-by : Andreas Rheinhardt <andreas.rheinhardt@gmail.com>
  
  Reviewed-by : Paul B Mahol <onemda@gmail.com>
  
  Signed-off-by : Michael Niedermayer <michael@niedermayer.cc>
  

  • [DH] libavformat/flacdec.c