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• How to make high smooth, high resolution particle motion animations

  5 décembre 2019, par algae

  For some time I have been having trouble with producing short movies/animations/gifs which are of sufficiently high resolution. I’m going to use R to generate some frames as a random example, but if there is somewhere else I should be creating frames from to give better results I would be interested in that too.

  Creating frames

  The kinds of animations I’m interested involve some cloud of ’particles’ moving about the page. There are usually a large number of particles and I would like their motion be as smooth as possible. As a random example, consider the R code (using base graphics and not ggplot2 as it is far quicker for saving a large number of frames)

  N <- 500
  
  nFrames <- 250
  
  points <- pracma::randp(n=N, r=1)
  
  rot <- function(p, a) { return(cbind(p[,1]*cos(a) - p[,2]*sin(a), p[,1]*sin(a) + p[,2]*cos(a))) }
  
  cols <- colorRampPalette(c("red", "green", "blue"))(nFrames)
  
  ang <- seq(0, pi, length=N)
  
  
  
  # Save frames
  
  png(filename="%d.png")
  
  par(mar=c(0,0,0,0))
  
  for (i in seq(1,N,length=nFrames)) 
  
          plot(sqrt(i)*rot(points, ang[i]), xlim=sqrt(N)*c(-1,1),  ylim=sqrt(N)*c(-1,1), cex=0.5, pch=19, col=cols[i], asp=1, xaxs="i")
  
  
  
  dev.off()

  Frames to animation

  There are a number of tools available to chain each frame together into an animation (in R there are also things like gganimate which I have tried but did not find convenient or better than the following). I also don’t have any requirements for the resulting file size or time taken to get everything looking as crisp as possible.

  convert

  For short gif style animations a common solution is to do something like convert -delay 1 -loop 0 *.png g.gif which gives

  

  gifski

  Running gifski -o g.gif *.png produces

  

  There is an annoying amount of ’jitter’ happening in the transition between frames in both of the above (though less noticeable with gifski).

  ffmpeg

  Being gifs, the above will be have limited options for tweaking so I suspect part of the solution lies in using ffmpeg. All I would like to know is how to make the animation appear totally smooth without any kind of noticeable blurriness. Here the resulting movies tend to be quite smooth, but resolution is lacking.. e.g. after setting height=1080 and width=1080 in png() of the above code we can run

  fmpeg -i %d.png -s 1080x1080 -c:v libx264 -vf fps=250 -pix_fmt yuv444p out.mp4

  If the particles move on a time/space scale smaller than is visible to the naked eye, and we set the frames per second to be the total number of frames, the transition between frames should be seamless, right ? At around the 2 second mark in out.mp4 you will see some kind of frame drop and similarly right at the beginning. Why does this happen ?

  Questions

  1. Is there a standard documented approach to generating high quality animations/movies involving large numbers of ’point-like’ particles ? Do we need more an more frames ?
  2. How to improve resolution of movies using ffmpeg ? Should I change from .png format to something vectorised (if so, how) ?

  Running Fedora v31.

• Python - playing video using ffplay displays file in larger resolution

  10 décembre 2019, par derBrain

  I’m working on a simple script that plays a video using ffplay.
  The problem I’m running into is that the output file has a larger resolution than it should have.
  The resolution of the file to be played is 1280x720, however, when I open the file with ffplay, the output is scaled to 1920x1080.
  I even tried to downscale the output by factor 1.5 (to get it to play in 1280x720), but the quality is noticeably worse compared to playing the same file in VLC player.
  What am I missing here ?

  This is the code I’m using :

  dbFile = "file.mp4"
  
  open_dbFile = "ffplay {0} -window_title {1} -left 50 -top 50 -nostats".format(dbFile, "DB_file")
  
  sub.Popen(open_dbFile)

  this is the log :

  ffplay version N-95171-g6ca3d34ff8 Copyright (c) 2003-2019 the FFmpeg developers
  
    built with gcc 9.2.1 (GCC) 20190918
  
  
  
  configuration: --enable-gpl --enable-version3 --enable-sdl2 --enable-fontconfig --enable-gnutls --enable-iconv --enable-libass --enable-libdav1d --enable-libbluray --enable-libfreetype --enable-libmp3lame --enable-libopencore-amrnb --enable-libopencore-amrwb --enable-libopenjpeg --enable-libopus --enable-libshine --enable-libsnappy --enable-libsoxr --enable-libtheora --enable-libtwolame --enable-libvpx --enable-libwavpack --enable-libwebp --enable-libx264 --enable-libx265 --enable-libxml2 --enable-libzimg --enable-lzma --enable-zlib --enable-gmp --enable-libvidstab --enable-libvorbis --enable-libvo-amrwbenc --enable-libmysofa --enable-libspeex --enable-libxvid --enable-libaom --enable-libmfx --enable-ffnvcodec --enable-cuvid --enable-d3d11va --enable-nvenc --enable-nvdec --enable-dxva2 --enable-avisynth --enable-libopenmpt --enable-amf
  
    libavutil      56. 35.100 / 56. 35.100
  
    libavcodec     58. 59.101 / 58. 59.101
  
    libavformat    58. 33.100 / 58. 33.100
  
    libavdevice    58.  9.100 / 58.  9.100
  
    libavfilter     7. 59.100 /  7. 59.100
  
    libswscale      5.  6.100 /  5.  6.100
  
    libswresample   3.  6.100 /  3.  6.100
  
    libpostproc    55.  6.100 / 55.  6.100
  
  
  
  Metadata:
  
      major_brand     : mp42
  
      minor_version   : 0
  
      compatible_brands: isommp42
  
      creation_time   : 2017-12-24T15:03:27.000000Z
  
    Duration: 00:08:36.83, start: 0.000000, bitrate: 588 kb/s
  
      Stream #0:0(und): Video: h264 (Main) (avc1 / 0x31637661), yuv420p(tv, bt709), 1280x720 [SAR 1:1 DAR 16:9], 459 kb/s, 29.97 fps, 29.97 tbr, 90k tbn, 59.94 tbc (default)
  
      Metadata:
  
        creation_time   : 2017-12-24T15:03:27.000000Z
  
        handler_name    : ISO Media file produced by Google Inc. Created on: 12/24/2017.
  
      Stream #0:1(und): Audio: aac (LC) (mp4a / 0x6134706D), 44100 Hz, stereo, fltp, 125 kb/s (default)
  
      Metadata:
  
        creation_time   : 2017-12-24T15:03:27.000000Z
  
        handler_name    : ISO Media file produced by Google Inc. Created on: 12/24/2017.
  
     1.59 A-V: -0.014 fd=   0 aq=   19KB vq=   30KB sq=    0B f=0/0

  Thanks for your help !
  db

• ffmpeg set output resolution by resizing image

  3 janvier 2020, par Martin

  I’m trying to use ffmpeg for rendering video where an audio file and image are taken as inputs, and turned into a video (basically a music video) with the audio file playing for the duration of the video.

  My current working command :

  ffmpeg -loop 1 -framerate 2 -i "front.png" -i "testWAVfile.wav" -vf "scale=2*trunc(iw/2):2*trunc(ih/2),setsar=1,format=yuv420p" -c:v libx264 -preset medium -tune stillimage -crf 18 -c:a aac -shortest -vf scale=1920:1080  "outputVideo.mp4"

  Will set the output resolution of the video to whatever the resolution of the image is. Is there a way I can resize the image to enlarge it by a couple multiplications so that the output video resolution will be higher ?

  Like if my front.png image was 800x800 pixels, I could add something to my ffmpeg command to triple the resolution, so that the output video resolution is 2400x2400 ?