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• Fast movie creation using MATLAB and ffmpeg

  24 février 2018, par hyiltiz

  I have some time series data that I would like to create into movies. The data could be 2D (about 500x10000) or 3D (500x500x10000). For 2D data, the movie frames are simply line plot using plot, and for 3D data, we can use surf, imagesc, contour etc. Then we create a video file using these frames in MATLAB, then compress the video file using ffmpeg.

  To do it fast, one would try not to render all the images to display, nor save the data to disk then read it back again during the process. Usually, one would use getframe or VideoWriter to create movie in MATLAB, but they seem to easily get tricky if one tries not to display the figures to screen. Some even suggest plotting in hidden figures, then saving them as images to disk as .png files, then compress them using ffmpeg (e.g. with x265 encoder into .mp4). However, saving the output of imagesc in my iMac took 3.5s the first time, then 0.5s after. I also find it not fast enough to save so many files to disk only to ask ffmpeg to read them again. One could hardcopy the data as this suggests, but I am not sure whether it works regardless of the plotting method (e.g. plot, surf etc.), and how one would transfer data over to ffmpeg with minimal disk access.

  This is similiar to this, but immovie is too slow. This post 3 is similar, but advocates writing images to disk then reading them (slow IO).

• Regarding rotation information when rotating a movie in Avfoundation

  15 août 2017, par howmanylife

  I was able to rotate the movie with the following code

  videoCompositionTrack.preferredTransform = CGAffineTransform(rotationAngle: CGFloat(M_PI_2))

  I confirmed the information of the rotated video by ffmpeg. Rotate in the tag does not fluctuate as shown below, but a tag called side_data_list was generated and the value of rotation in side_data_list fluctuated, while keeping the information of rotate in tag unchanged.I want to change "tag" information.

  "tags": {
  
                  "rotate": "90"
  
          },
  
  "side_data_list": [
  
                  {
  
  "rotation": -90
  
                  }

  Are there any good advice on AVFoundation and ffmpeg ?

• ffmpeg yuvj422p color movie conversion avi2ogv

  28 juillet 2017, par 7Tonin

  While converting avi video to ogv, there is a color problem in output file.
  How can I solve this issue ?
  normal colors altered colors

  Actually a part of the problem is from the player - so weak question

  Command using ffmpeg-3.3.2-1.mga6.tainted :

  ffmpeg -i dscn0146.avi -pix_fmt yuv422p -s 640x480 dscn0146_hq.ogv -y

  And input metadata :

  Guessed Channel Layout for Input Stream #0.1 : mono
  
  Input #0, avi, from 'dscn0146.avi':
  
    Metadata:
  
      encoder         : 
  
      maker           : NIKON
  
      model           : COOLPIX S3500
  
      creation_time   : 2017-07-22 12:09:06
  
    Duration: 00:00:07.33, start: 0.000000, bitrate: 11091 kb/s
  
      Stream #0:0: Video: mjpeg (MJPG / 0x47504A4D), yuvj422p(pc, bt470bg/unknown/unknown), 640x480, 10770 kb/s, 30 fps, 30 tbr, 30 tbn, 30 tbc
  
      Stream #0:1: Audio: pcm_s16le ([1][0][0][0] / 0x0001), 22050 Hz, mono, s16, 352 kb/s
  
  Stream mapping:
  
    Stream #0:0 -> #0:0 (mjpeg (native) -> theora (libtheora))
  
    Stream #0:1 -> #0:1 (pcm_s16le (native) -> vorbis (libvorbis))

  Processes normaly, but fires a warning :

  [swscaler @ 0xd3c3a0] deprecated pixel format used, make sure you did set range correctly

  Output metadata :

  Output #0, ogv, to 'dscn0146_hq.ogv':
  
    Metadata:
  
      model           : COOLPIX S3500
  
      maker           : NIKON
  
      encoder         : Lavf57.71.100
  
      Stream #0:0: Video: theora (libtheora), yuv422p(progressive), 640x480, q=2-31, 200 kb/s, 30 fps, 30 tbn, 30 tbc
  
      Metadata:
  
        encoder         : Lavc57.89.100 libtheora
  
        model           : COOLPIX S3500
  
        maker           : NIKON
  
      Stream #0:1: Audio: vorbis (libvorbis), 22050 Hz, mono, fltp
  
      Metadata:
  
        encoder         : Lavc57.89.100 libvorbis
  
        model           : COOLPIX S3500
  
        maker           : NIKON