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• Yes or no, will ffmpeg api do hardware decoding on iOS ?

  15 janvier 2019, par Fattie

  There seems to be conflicting information on this.

  https://trac.ffmpeg.org/wiki/HWAccelIntro

  notice the first diagram, it firmly marks iOS as “Y” on VideoToolbox

  

  however in the comments down the bottom it says

  VideoToolbox. ​VideoToolbox, only supported on macOS. H.264 decoding is available in FFmpeg/libavcodec.

  And in the confusing second diagram it says "Standalone" is not done for VideoToolbox.

  We have found that using ffmpeg compiled in to iOS .... it seems to not use hardware decoding, which is really a pain.

  1. With avcodec_get_hw_config() we get AV_PIX_FMT_VIDEOTOOLBOX, AV_HWDEVICE_TYPE_VIDEOTOOLBOX which is seemingly correct.

  2. But usage and framerates clearly shows everything is being done in CPU. The code is in ff_hevc_hls_residual_coding all the time. (That’s fffmpeg’s software decoder.)

  3. This very diff very long git.videolan.org URL here seems to suggest again it should all be working.

  4. Have tried every iPhone etc. of course

• FFmpeg LGPL build

  27 février 2014, par user1149520

  Hello I'm trying to build ffmpeg under the LGPL license but I'm having trouble creating the dll's.

  I'm building the source on the Windows platform using MinGW and I use the configure options below to build the latest snapshot

  ./configure --enable-memalign-hack --enable-pthreads --disable-shared

  However when I make and install from this I only get the "avdevice-53.dll" and none of the others such as avcodec or avformat. Is there something else I need to do to be able to make these files ?

• 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.