Recherche avancée

Sur d’autres sites (11884)

• FFmpeg output video file much smaller than uncompressed input audio file, using option to preserve original audio quality

  17 mars 2021, par Jan

  I attempt to create a video slideshow from a number of image files and an audio file in 2 steps :

  


  

  1. Create a temporary video file from a sequence of image files

  


  2. Add an audio file to the temporary video file with a delay of 5 seconds

  


  


  The audio file is an uncompressed stereo wav file, encoded with a sample rate of 44100 Hz and a bit depth of 32 bits, with a size of 40.1 MB. To preserve the lossless quality of the input audio file I use the option -c:a aac -b:a 192k as per Slideshow Wiki. However, the final output video file has a size of only 4.49 MB.

  


  How can the output video file be about 10 times smaller than the input audio file and still preserve the original lossless quality ?

  


  My code :

  


  ffmpeg -f concat -i slide-sequence.txt -c:v libx264 -r 30 -filter_complex format=yuv420p temp.mp4
ffmpeg -i temp.mp4 -i audio.wav -af "adelay=5000|5000" -c:v copy -c:a aac -b:a 192k out.mp4


  


• ffmpeg - multiple output with thumbnails

  9 décembre 2016, par Thomas

  I would like ffmpeg to do the following :

  • read an input mp4 (-i movie.mp4)
  • skip the first 5 seconds (-ss 5)
  • find scene changes and display the frame numbers (-vf "select=gt(scene\, 0.4, showinfo))
  • output #1 - a gif file (output.gif)
  • output #2 - a contact sheet with all the thumbnails (-vf "select scale=320 :-1, tile=12x200" thumbnails.png)

  This will generate the thumbnails :

  ffmpeg -hide_banner -i d:/Test/movie01.mp4 -ss 5 -vf "select=gt(scene\,0.4), showinfo, scale=320:-1, tile=12x200" -vsync 0 thumbnails%03d.png

  this will generate the gif :

  ffmpeg -hide_banner -i d:/Test/movie01.mp4 -ss 5 -vf "select='not(mod(n,60))',setpts='N/(30*TB)', scale=320:-1" -vsync 0 output.gif

  I would like to do both at once with 2 more features :

  • set fps and resolution for the gif ; I would like the gif to represent the whole movie in X seconds, at Y fps (I know the duration of the input movie so I can calculate how often a frame needs to be captured)

  • set the width only for the thumbnail picture (tile=12 for example) and let ffmpeg determine the appropriate height

  I have tried to compose a command line from what I read on this page : https://trac.ffmpeg.org/wiki/Creating%20multiple%20outputs, using the split / map commands but I couldn’t get it to work

• Fast seeking ffmpeg multiple times for screenshots

  14 septembre 2021, par user3786834

  I have come across https://askubuntu.com/questions/377579/ffmpeg-output-screenshot-gallery/377630#377630, it's perfect. That has done exactly what I wanted.

  



  However, I'm using remote URLs to generate the screenshot timeline. I do know it's possible to fast seek with remote files using https://trac.ffmpeg.org/wiki/Seeking%20with%20FFmpeg (using -ss before the -i) but this only runs the once.

  



  I'm looking for a way to use the

  



  ./ffmpeg -i input -vf "select=gt(scene\,0.4),scale=160:-1,tile,scale=600:-1" \
-frames:v 1 -qscale:v 3 preview.jpg


  



  command but using the fast seek method as it's currently very slow when used with a remote file. I use PHP but I am aware that a C method exists by using av_seek_frame, I barely know C so I'm unable to implement this into a PHP script I'm writing. So hopefully, it is possible to do this directly with ffmpeg in the PHP system() function.

  



  Currently, I run seperate ffmpeg commands (with the -ss method) and then combine the screenshots together in PHP. However, with this method it will be refetching the metadata each time and a more optimized method would be to have it all happen in the same command line because I want to reduce the amount of requests made to the remote url so I can run more scripts in sequence with each other.

  



  Thank you for your help.