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• FFMPEG : How to create a webp preview file with 16:9 aspect ratio without stretching

  30 août 2018, par A - O

  

  How to make something like this by using FFMPEG ?

  I’m trying to create a webp file for videos to show a quick preview of them like Youtube with 16:9 aspect ratio and black/blurred background

  This following script is what I have done and it works, But when the video’s width and height are like this [W:350 H:196] I get this following error.

  Error :

  [Parsed_crop_5 @ 000002438207c580] Invalid too big or non positive size for width '350' or height '196'

  ---

  FFMPEG script

  ffmpeg -r 16 -ss 0 -i <input file="file" /> -loop 0 -c:v libwebp -lavfi "[0:v]scale=ih*16/9:-1,boxblur=luma_radius=min(h\,w)/20:luma_power=1:chroma_radius=min(cw\,ch)/20:chroma_power=1[bg];[bg][0:v]overlay=(W-w)/2:(H-h)/2,setpts=0.3*PTS,scale=350:-1,crop=h=iw*9/16" -vb 800K -t 00:00:03 out.webp -y

  The main problem is this, Ignore other parameters like infinite loop,t, frame rate...

  crop=h=iw*9/16

  In my opinion, some quantities are large floats and that’s why I’m getting this error.

• Set Ratio for UDP Stream with VideoCapture in Opencv4nodejs

  31 juillet 2018, par Felix Bäder

  I currently try to analyse screenshots of a udp stream with opencv.

  Currently I’m using a shell script with ffmpeg to generate an image and saving this to my disk with 1 fps then I read this with opencv4nodejs. But i think this is not the best pratice.

  I’m using opencv4nodejs : https://github.com/justadudewhohacks/opencv4nodejs

  Now I tired to use the VideoCapture function of opencv.

  For debugging I currently open the stream, take a screenshot and save it to disk.

  const cv   = require('opencv4nodejs');
  
  const vCap = new cv.VideoCapture('udp://239.1.1.1:6670');
  
  
  
  let frame;
  
  
  
  class Streamer {
  
  
  
      streamTest () {
  
          frame = vCap.read();
  
          cv.imwrite('./resources/output.png', frame);
  
      };
  
  }
  
  
  
  module.exports = Streamer;

  If I’m using the UDP stream the ration aspect is wrong and always set to 4:3 but the stream displays an 16:9 image.

  I can resize the frame, but this isn’t a suitable solution for this case cause I also getting 4:3 images within this stream.

  How can I analyse the frames from the udp stream with right ratio ?

  btw. I also can’t change the fps for the udp stream using

  .set(cv.CAP_PROP_FPS, 1); 

  This only works, if I’m using the stream of a connected webcam.

  const vCap = new cv.VideoCapture(0);

• ffmpeg : thumbnail of frame, preserve aspect ratio, apply background / padding / fill colour

  4 juin 2018, par Pistos

  I already have found out how to scale the thumbnail to stay within specified bounding dimensions while maintaining aspect ratio. For example, to get the frame shown at 6 seconds into the input.mp4 video file, and scale it to fit into 96x60 (16:10 aspect ratio) :

  ffmpeg -y -i input.mp4 -ss 6 -vframes 1 -vf scale="'if(gt(a,16/10),96,-1)':'if(gt(a,16/10),-1,60)'" output.png

  This is fine, it works.

  Next, I would like to do the same, but if the video’s aspect ratio is not exactly 16:10, then I would like to force the output image to have an aspect ratio of 16:10 by taking the above transformation, and filling or padding the space with white. That is, I want the output to be as if I took, say, a 96x48 image, and laid it over a 96x60 white background, resulting in white bars above and below the 96x48 image.

  Ideally, I do not want to resort to using another tool or library, such as ImageMagick. It would be best if ffmpeg could do this on its own.