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• grab_image is not working for HD videos ?

  21 février 2012, par user1222769

  I am using ffmpeg command for grab_image of converted videos which are in flv format. All videos images are created except for HD videos. The code which i have written is as follws. Thanks in advance.

  function grab_image($filename, $rootpath, $inputpath,$outputpath, $no_of_thumbs, $frame_number, $image_format, $width, $height)
  
  
  
  
  
      $_rootpath = $rootpath."\ffmpeg";
  
      // Media Size
  
      $size = $width."x".$height;
  
  
  
      // I am using static image, you can dynamic it with your own choice.
  
      $out=explode(".",$filename);
  
  
  
      $outfile = $out[0].".jpg";
  
  
  
      //$ffmpegcmd1="ffmpeg -i ".$inputpath."/".$filename." -ss 1.4 -vframes 1 -f image2 ". $outputpath."/".$outfile;
  
  
  
          // in local
  
  
  
             $ffmpegcmd1="D:/xampp/htdocs/abc/ffmpeg -i ".$inputpath."/".$filename." -r 1 -ss 1.4 -vframes 1 -f image2 ". $outputpath."/".$outfile;
  
      $ret = exec($ffmpegcmd1);
  
  
  
      // Execute this command using exec command or any other tool to grab image from converted flv file.
  
      return $ffmpegcmd1;
  
  }
  

• ffmpeg for merging vfr videos

  20 avril 2021, par Rupsha Chaudhuri

  I'm trying to generate a timelapse with images taken roughly at 10 Hz and for about an hour. Maintaining the relative timestamps is important. So I've split the images into roughly 1 min chunks and I generated 60 small videos in parallel (I've handled the duration for the boundary images). After that I stitch the videos. However when I look at the final contiguous video I realize that at the chunk boundaries after stitching the video either has an extra frame or falls behind the images.. the timestamps don't line up.

  


  The smaller videos are variable frame rate, so I convert them to mpeg-ts before applying the concat protocol to merge them.

  


  


  


  Generate small video:
ffmpeg -f concat -safe 0 -i input.txt -vsync vfr -pix_fmt yuv420p output.mp4

Convert to mpeg-ts
ffmpeg -i output.mp4 -c copy -bsf h264_mp4toannexb output.ts

Merge multiple small mpeg-ts videos
ffmpeg -i input.txt -c copy final_output.mp4

  


  


  



• What are good settings for transcoding videos uploaded to my app ?

  14 mai 2020, par Dmitry Minkovsky

  I am working on an app that allows users to share videos. The problem is that many videos are very high bitrate. For example, A 4-minute H264 video from an old iPhone is encoded at 1080p and runs 17,000 kb/s ( 500 megabytes). Accepting and distributing such videos at this bitrate/resolution is not practical for a social application.

  



  I have been playing with ffmpeg to transcode videos to smaller sizes and higher compression, but have not achieved acceptable results. For example :

  



  ffmpeg \
    -i in.mov \
    -vf scale=w='if(gt(iw\,ih)\,780\,-2)':h='if(gt(iw\,ih)\,-2\,780)' \ 
    -c:v libx264 \
    -crf 28 \
    -preset medium \
    -pix_fmt yuv420p \
    -movflags +faststart \
    out.mp4


  



  This command transcodes the above-mentioned 500MB file down to 70MB. It scales the larger dimension of the video to 780 pixels and compresses the video quite a bit. The results are okay, but the file is still large.

  



  Taking the longer dimension down to 480 pixels, the file is reduced to 40MB. Still quite large, and now significantly degraded. Also, the transcoding still takes quite a long time : about 1-1.5x on my 4 year old i7 Macbook Pro with 16GB RAM.

  



  I'm not sure how to improve on this. H265 is not supported in browsers. I am wondering :

  



  

  • How can I reduce size further ?

  


  • How can I transcode faster than 1x without significantly reducing quality ? Even 2-3x doesn't seem great ?

  


  



  Is this as good as it gets ?