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• How to set the value of an arbitrary pixel in ffmpeg ?

  14 mai 2017, par Neb

  I want to modify the rgb value of each pixel inside ffmpeg.

  I need to implement the following function :

  A[x + expr_1][y] = expr_2

  where x and y are the current sampled pixel, A is the input frame whose pixel need to be modified and expr_1, expr_2 are two independent expressions.

  I tried using the geq filter but it seems there no way to set the value of a pixel other than from that currently sampled. For istance, the function p(x,y) only returns the value of the pixel at the specified location, but doesn’t allow to set a value for that pixel. In other word, ffmpeg seems allowing only something like :

  A[x][y] = expr

  Is there a way to tell ffmpeg to set the value of a specific pixel ?

  Thanks for your time.

• Using ffmpeg to convert mp3 to mp4 - how to draw filename on generated video ?

  22 mai 2020, par akouris

  Using trial and error I am using the following script on an OSX, to bulk convert a whole folder full of mp3 files, to mp4, by looping a specific video file :

  



  for i in *.mp3; do /usr/local/bin/ffmpeg -stream_loop -1 -i /path_to_filename.mp4 -c copy -v 0 -f nut - | /usr/local/bin/ffmpeg -thread_queue_size 10K -i - -i "$i" -c copy -map 0:v -map 1:a -shortest "$(basename "$i" )".mp4 ; done; for f in *.mp3.mp4; do mv -v "$f" "${f/.mp3.mp4/.mp4}"; done


  



  How can I also print/add/burn the mp3 filename, without the extension (.mp3), as an additional video layer at the bottom of the generated video screen, and with the added difficulty of word wrapping the text if is too long ?

  


• Is H.264 used with CRF 0 really strictly lossless ?

  23 décembre 2017, par Mephisto

  I am surprised by how small files are when encoded in ffmpeg with the libx264 codec in Constant Rate Factor mode equals zero (-crf 0) that, according to the documentation, is "lossless".

  I would like to make sure what the word "lossless" here means. I would like to know if it follows my personal definition of lossless video : After encoding a video, you can confidently bet the life of your mother that, once you play it, the numerical values in the pixels of the restored video will be identically equal (within maybe a factor 0.00001 due to the floating point arithmetic) to the original.

  Does the H.264 lossless encoding follow my definition, or do they call it "lossless" because it is visually very close, very beautiful, whatever... ?