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• Android OpenCV - How can i read video files with using jni ?

  20 juin 2017, par Tiga

  I am developing an application using Android Opencv.

  This app, which I am developing, offers two operations.

  • The frame read from the camera is passed to Jni using native function
    Mat.getNativeObjAddr (), and the new image is returned through
    javaCameraView’s onCameraFrame() function
  • It reads a video clip inside Storage, processes each frame the same
    as # 1, and returns the resulting image via the onCameraFrame()
    function.

  First,function is implemented as simple as the following and works normally :

     @Override
  
      public Mat onCameraFrame(CameraBridgeViewBase.CvCameraViewFrame inputFrame) 
  
      {
  
          if(inputFrame!=null){
  
                  Detect(inputFrame.rgba().getNativeObjAddr(), boardImage.getNativeObjAddr());
  
              }
  
              return boardImage;
  
          }
  
      }

  However, the problem occurred in the second operation.
  As far as I know, the files inside Java Storage are not readable by jni.

  I already tried FFmpegMediaPlayer or MediaMetadataRetriever through Google search. However, the getFrameAtTime () function provided by this MetadataRetriever took an average of 170ms when grabbing a bitmap to a specific frame of 1920 * 1080 image. What I have to develop is to show the video results in real time at 30 fps. In # 1, the native function Detect () takes about 2ms to process one frame.

  For these reasons, I want to do this.

  java sends a video’s path (eg : /storage/emulated/0/download/video.mp4) to jni, and native functions process the video one frame at a time, and display the result image on ’onCameraFrame’.

  Is there a proper way ? I look forward to your reply. Thank you !

• Webcam streaming from Mac using FFmpeg

  13 décembre 2019, par Galaxy

  I want to stream my webcam from Mac using FFmpeg.

  First I checked the supported devices using ffmpeg -f avfoundation -list_devices true -i ""

  Output :

  [AVFoundation input device @ 0x7fdf1bd03000] AVFoundation video devices:
  
  [AVFoundation input device @ 0x7fdf1bd03000] [0] USB 2.0 Camera #2
  
  [AVFoundation input device @ 0x7fdf1bd03000] [1] FaceTime HD Camera
  
  [AVFoundation input device @ 0x7fdf1bd03000] [2] Capture screen 0
  
  [AVFoundation input device @ 0x7fdf1bd03000] [3] Capture screen 1
  
  [AVFoundation input device @ 0x7fdf1bd03000] AVFoundation audio devices:
  
  [AVFoundation input device @ 0x7fdf1bd03000] [0] Built-in Microphone

  The device[0] is the webcam I want to use.

  ---

  Then I tried to capture the webcam using ffmpeg -f avfoundation -i "0" out.mpg

  Output :

  [avfoundation @ 0x7fe7f3810600] Selected framerate (29.970030) is not supported by the device
  
  [avfoundation @ 0x7fe7f3810600] Supported modes:
  
  [avfoundation @ 0x7fe7f3810600]   320x240@[120.101366 120.101366]fps
  
  [avfoundation @ 0x7fe7f3810600]   640x480@[120.101366 120.101366]fps
  
  [avfoundation @ 0x7fe7f3810600]   800x600@[60.000240 60.000240]fps
  
  [avfoundation @ 0x7fe7f3810600]   1024x768@[30.000030 30.000030]fps
  
  [avfoundation @ 0x7fe7f3810600]   1280x720@[60.000240 60.000240]fps
  
  [avfoundation @ 0x7fe7f3810600]   1280x1024@[30.000030 30.000030]fps
  
  [avfoundation @ 0x7fe7f3810600]   1920x1080@[30.000030 30.000030]fps
  
  [avfoundation @ 0x7fe7f3810600]   320x240@[30.000030 30.000030]fps
  
  [avfoundation @ 0x7fe7f3810600]   640x480@[30.000030 30.000030]fps
  
  [avfoundation @ 0x7fe7f3810600]   800x600@[20.000000 20.000000]fps
  
  [avfoundation @ 0x7fe7f3810600]   1024x768@[6.000002 6.000002]fps
  
  0: Input/output error

  ---

  After that, I tried stream this webcam from my Mac using ffmpeg -f avfoundation -framerate 30 -i "0" -f mpeg1video -b 200k -r 30 -vf scale=1920:1080 http://127.0.0.1:8082/

  Output :

  [avfoundation @ 0x7f8515012800] An error occurred: The activeVideoMinFrameDuration passed is not supported by the device.  Use -activeFormat.videoSupportedFrameRateRanges to discover valid ranges.0: Input/output error

  ---

  I cannot capture or stream this webcam. However when I used the Facetime camera instead of this webcam, everything was OK. I’ve been searching for this problem for a few days, but still cannot fix it. Does anyone have experience with webcam and FFmpeg on Mac ?

• FFMPEG filtergraph 'warning, too many B-frames in a row' [on hold]

  26 juin 2017, par Leif Andersen

  I am trying to append two videos together with FFmpeg’s filtergraph. One video is sized 1920x1080 at 30fps, and another 1280x720 at 25fps. Both use yuv420p, and have the same pixel densities. I am currently ignoring the audio tracks. The following is my filtergraph :

  [video2]fifo[video3];
  
  [video3]pad=width=1920:height=1080[video9];
  
  [video9]fps=fps=25[video11];
  
  [video11]setpts=expr=PTS-STARTPTS[video17];
  
  
  
  [video6]fifo[video7];
  
  [video7]pad=width=1920:height=1080[video13];
  
  [video13]fps=fps=25[video15];
  
  [video15]setpts=expr=PTS-STARTPTS[video19];
  
  
  
  [video17][video19]concat=v=1:a=0:n=2[video21];
  
  [video21]pad=width=1920:height=1080[video23];
  
  [video23]fps=fps=25[video25];
  
  [video25]format=pix_fmts=yuv420p[video27]

  The first chain tries to convert the first video into a common format, that starts at 0 for the concat filter. The second chain does the same as the first. Finally, the third chain concatenates them videos together, and sets some properties for the resulting playlist.

  Unfortunately, when I run this error, ffmpeg repeatedly outputs :

  [mpeg4 @ 0x7fc16a810600] warning, too many B-frames in a row

  When finished, I see the first video, padded to the correct resolution and frame rate, but instead of the second Video I see black. Additionally, the entire video is several days in length, starting with the first Video and ending in several days of just black.

  I cannot figure out why I am getting this error, as it seems like I am setting the videos to have identical properties. What am I missing ?

  Also, for what its worth, I am using FFmpeg’s C API rather than the command line tool. I am using libavformat/libavcodec/libavutil to do the encoding/decoding and libavfilter for the filtergraph.