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• using ffmpeg to create a wavefile image from opus

  29 décembre 2015, par edwardsmarkf

  I have been trying to use ffmpeg to create a wavefile image from an opus file. so far i have found three different methods but cannot seem to determine which one is the best.

  The end result is hopefully to have a sound-wave that is only approx. 55px in height. The image will become part of a css background-image.

  Adapted from Generating a waveform using ffmpeg :

  ffmpeg -i file.opus -filter_complex
  "showwavespic,colorbalance=bs=0.5:gm=0.3:bh=-0.5,drawbox=x=(iw-w)/2:y=(ih-h)/2:w=iw:h=1:color=black@0.5"
  file.png

  which produces this image :
  

  Next, I found this one (and my favorite because of the simplicity) :

  ffmpeg -i test.opus -lavfi showwavespic=split_channels=1:s=1024x800 test.png

  And here is what that one looks like :

  

  Finally, this one from FFmpeg Wiki : Waveform, but it seems less efficient using a second utility (gnuplot) rather than just ffmpeg :

  ffmpeg -i file.opus -ac 1 -filter:a
  aresample=4000 -map 0:a -c:a pcm_s16le -f data - | \
  gnuplot -e "set
  terminal png size 525,050 ;set output
  ’file.png’ ;unset key ;unset tics ;unset border ; set
  lmargin 0 ;set rmargin 0 ;set tmargin 0 ;set bmargin 0 ; plot ’

  

  Option two is my favorite, but i dont like the margins on the top and bottom of the waveforms.

  Option three (using gnuplot) makes the best ’shaped’ image for our needs, since the initial spike in sound seems to make the rest almost too small to use (lines tend to almost disappear) when the image is sized at only 50 pixels high.

  Any suggestions how might best approach this ? I really understand very little about any of the options I see, except of course for the size. Note too i have 10’s of thousands to process, so naturally i want to make a wise choice at the very beginning.

• Embedding many small movies in page (gif vs mp4 vs webm vs ?)

  25 mars 2017, par genekogan

  I am making a webpage which will contain around 20-25 small-resolution ( 56x56) and short-length ( 3 sec) movies which will be set to autoplay and loop, so they will be looping on the page at all times. They are mostly dispersed throughout the page, so cannot easily be merged into bigger movies.

  I’m trying to decide on the right format to use, balancing filesize, quality, and processor overhead.

  mp4 seems the best option in terms of quality and filesize, however embedding many small mp4s on the page felt to me slow and made my computer get hot. Despite the fact that if they were one mp4, it would be only around 300x240 — it seems there is a lot of CPU overhead if they are divided.

  gif is lower quality and bigger filesize, but the CPU performance felt smoother. I can’t prove it though because I didn’t measure it — are gif’s known to be better performance than mp4 ?

  I have not tried other formats (webm, avi, ogg, etc) but I am unsure of how supported all of these formats are by most browsers and I want the webpage to be viewable from multiple browsers/countries.

  How can I determine the best format to use for these videos ? Is there a tool which can measure the CPU performance of my webpage so I can quantify the performance issues ?

• ffmpeg selects shortest movie but leaves full length audio

  26 octobre 2015, par Stan James

  I’ve created a tool to create a grid of movies, like in the Brady Bunch opening. It’s a cool, funny effect.

  Here’s a sample movie showing the grid.

  

  The problem is that ffmpeg is choosing the shortest movie to determine the maximum length of overlaid videos, but still using the full length of the first audio track to determine the overall output movie length.

  So all my videos stop moving when the shortest one ends, but the audio plays on for full length of the first movie.

  How can I either (1) set the length of the output movie to the longest input movie or (2) match the audio length to the shortest movie length as well ?

  Gist of my script.

  Based on this ffmpeg example usage which exhibits the same audio problem :

  ffmpeg
  
      -i 1.avi -i 2.avi -i 3.avi -i 4.avi
  
      -filter_complex "
  
          nullsrc=size=640x480 [base];
  
          [0:v] setpts=PTS-STARTPTS, scale=320x240 [upperleft];
  
          [1:v] setpts=PTS-STARTPTS, scale=320x240 [upperright];
  
          [2:v] setpts=PTS-STARTPTS, scale=320x240 [lowerleft];
  
          [3:v] setpts=PTS-STARTPTS, scale=320x240 [lowerright];
  
          [base][upperleft] overlay=shortest=1 [tmp1];
  
          [tmp1][upperright] overlay=shortest=1:x=320 [tmp2];
  
          [tmp2][lowerleft] overlay=shortest=1:y=240 [tmp3];
  
          [tmp3][lowerright] overlay=shortest=1:x=320:y=240
  
      "
  
      -c:v libx264 output.mkv