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• ffmpeg png to png quality loss

  13 avril 2018, par kilo

  I did a python script that managed to unshuffle a shuffled (png) image according to a specific pattern, that python script uses ffmpeg and does 12 encodes to unshuffling it (by cropping a specific part and pasting it over the existing picture).
  As such the same file is re-encoded into a new file each time, which shouldn’t be a problem since i am doing png conversion (lossless, right ?), but i still lose quality on it.

  Here are the pictures :

  • https://i.imgur.com/TMzBUGq.png (input)
  • https://i.imgur.com/FCwfViJ.png (output)

  Notice the loss of quality on the "ONE PUNCH MAN" text. The rest of the picture is, seemingly, literally identical. So the problem seems to be with the colors.

  Here are the ffmpeg commands i ran to get to the output :

  ffmpeg -loglevel panic -y -i "output/001.png" -i "001.png" -qscale:v 2 -filter_complex "[0:v]crop=200:280:200:0[t];[0:v][t]overlay=0:280" "output/001.png"
  
  ffmpeg -loglevel panic -y -i "output/001.png" -i "001.png" -qscale:v 2 -filter_complex "[0:v]crop=200:280:400:0[t];[0:v][t]overlay=0:560" "output/001.png"
  
  ffmpeg -loglevel panic -y -i "output/001.png" -i "001.png" -qscale:v 2 -filter_complex "[0:v]crop=200:280:600:0[t];[0:v][t]overlay=0:840" "output/001.png"
  
  ffmpeg -loglevel panic -y -i "output/001.png" -i "001.png" -qscale:v 2 -filter_complex "[1:v]crop=200:280:0:280[t];[0:v][t]overlay=200:0" "output/001.png"
  
  ffmpeg -loglevel panic -y -i "output/001.png" -i "001.png" -qscale:v 2 -filter_complex "[0:v]crop=200:280:400:280[t];[0:v][t]overlay=200:560" "output/001.png"
  
  ffmpeg -loglevel panic -y -i "output/001.png" -i "001.png" -qscale:v 2 -filter_complex "[0:v]crop=200:280:600:280[t];[0:v][t]overlay=200:840" "output/001.png"
  
  ffmpeg -loglevel panic -y -i "output/001.png" -i "001.png" -qscale:v 2 -filter_complex "[1:v]crop=200:280:0:560[t];[0:v][t]overlay=400:0" "output/001.png"
  
  ffmpeg -loglevel panic -y -i "output/001.png" -i "001.png" -qscale:v 2 -filter_complex "[1:v]crop=200:280:200:560[t];[0:v][t]overlay=400:280" "output/001.png"
  
  ffmpeg -loglevel panic -y -i "output/001.png" -i "001.png" -qscale:v 2 -filter_complex "[0:v]crop=200:280:600:560[t];[0:v][t]overlay=400:840" "output/001.png"
  
  ffmpeg -loglevel panic -y -i "output/001.png" -i "001.png" -qscale:v 2 -filter_complex "[1:v]crop=200:280:0:840[t];[0:v][t]overlay=600:0" "output/001.png"
  
  ffmpeg -loglevel panic -y -i "output/001.png" -i "001.png" -qscale:v 2 -filter_complex "[1:v]crop=200:280:200:840[t];[0:v][t]overlay=600:280" "output/001.png"
  
  ffmpeg -loglevel panic -y -i "output/001.png" -i "001.png" -qscale:v 2 -filter_complex "[1:v]crop=200:280:400:840[t];[0:v][t]overlay=600:560" "output/001.png"

  Anyone got any idea why is there this quality loss ?
  Strangely enough, there is no quality loss when i do it in an entirely different way (crop each square into an individual file, then each of them are put into a 1x2 vstack with the next one, then each of the resulting 1x2 files are vstacked with a second file to make a 1x4 file, then each of those are hstacked to make a 2x4 file, and finally we hstack the two resulting file for the resulting 4x4 output), even though there is more than double the amount of encodes.

• Produce waveform video from audio using FFMPEG

  30 novembre 2020, par RhythmicDevil

  I am trying to create a waveform video from audio. My goal is to produce a video that looks something like this

  


  

  


  For my test I have an mp3 that plays a short clipped sound. There are 4 bars of 1/4 notes and 4 bars of 1/8 notes played at 120bpm. I am having some trouble coming up with the right combination of preprocessing and filtering to produce a video that looks like the image. The colors dont have to be exact, I am more concerned with the shape of the beats. I tried a couple of different approaches using showwaves and showspectrum. I cant quite wrap my head around why when using showwaves the beats go past so quickly, but using showspectrum produces a video where I can see each individual beat.

  


  ShowWaves

  


  ffmpeg -i beat_test.mp3 -filter_complex "[0:a]showwaves=s=1280x100:mode=cline:rate=25:scale=sqrt,format=yuv420p[v]" -map "[v]" -map 0:a output_wav.mp4


  


  This link will download the output of that command.

  


  ShowSpectrum

  


  ffmpeg -i beat_test.mp3 -filter_complex "[0:a]showspectrum=s=1280x100:mode=combined:color=intensity:saturation=5:slide=1:scale=cbrt,format=yuv420p[v]" -map "[v]" -an -map 0:a output_spec.mp4


  


  This link will download the output of that command.

  


  I posted the simple examples because I didn't want to confuse the issue by adding all the variations I have tried.

  


  In practice I suppose I can get away with the output from showspectrum but I'd like to understand where/how I am thinking about this incorrectly. Thanks for any advice.

  


  Here is a link to the source audio file.

  


• ffmpeg x11grab moov atom not found

  30 mars 2021, par Jintor

  2 FFMPEG process

  


  (1) generating a ffmpeg x11grab to a .mp4
(2) take the .mp4 and restream it simultaneously to multiple rtmp endpoints

  


  ISSUE the generated file in (1) have this error "moov atom not found"

  


  This is the command that generate (1) :

  


  ffmpeg -re -y -f x11grab -draw_mouse 0 -framerate 30 
-video_size $RESOLUTION -i :$DISPLAY_NUM -c:a aac -c:v libx264 
-movflags +faststart -preset ultrafast -crf 28 -refs 4 -qmin 4 
-pix_fmt yuv420p -filter:v fps=30 file.mp4


  


  in the (2) => when I try to ffmpeg -i file.mp4 output somewhere : I get "moov atom not found" so the (2) can't read or open (1).

  


  What I'm I missing

  


  in (1) -movflags +faststart doesn't seem to fix the issue

  


  ••••••• EDIT : more details on the context ••••••

  


  I'm using openvidu : webrtc with kurento and coturn.

  


  The record feature creates a .mp4 on the fly as the chat is going on.

  


  To start the recording, there is an API call i can make to my server and it automatically stops when all users leaves the chatroom OR do an other api call to stop. see composed video in this link https://docs.openvidu.io/en/2.17.0/advanced-features/recording/

  


  openvidu have also webhooks.

  


  My problem is not how to stop ffmpeg, but getting FFMPEG to encode while the mp4 or other is being generated "on the fly".

  


  There is 2 options :

  


  OPTION 1 : individual => 1 .webm per camare => this .webm ffmpeg can restream as hls or RTMP => it's working.

  


  OPTION 2 : ** but the issue is with "Composed" video => it's using ffmpeg to x11grab the session... but it's mp4 without moov ato, so ffmpeg don't do anything with this.

  


  see the composed.sh script here
https://github.com/OpenVidu/openvidu/blob/master/openvidu-server/docker/openvidu-recording/scripts/composed.sh