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• Aligning multiple words vertically with drawtext & ffmpeg

  26 mai 2023, par CRAIG

  I am needing to vertically align several drawtext chained commands that are of various font sizes off of a center point, but in a way where similar fonts/sizes will appear to be correctly aligned off of their baselines.

  


  The $centerline is a vertical top positioned line that theoretically is the vertical center that each text would sit upon regardless of total text height/font size so even differing fonts of differing sizes will look good together.

  


  But the max_glyph_a is to ensure that the same fonts with the same font size will sit on the same baseline. I would think this would do it, but no, it's off vertically.

  


   $y = '(' . $centerline . '+(text_h/2)-max_glyph_a)';


  


  I can't wrap my noggin around this. Any ideas ?

  


• How to add a watermark using FFmpeg ? [duplicate]

  19 février 2018, par eRROR.AuX

  This question already has an answer here :

  • How to add transparent watermark in center of a video with ffmpeg ?
    
    1 answer
    

  How to add watermark to this code :

   $shel = shell_exec(“$ffmpeg_b -y -i $video_file_full_path -vcodec
  
    libx264 -preset {$pt->config->convert_speed} -s 640×360 -crf 24
  
    $video_output_full_path_360 2>&1”);

• Gallery of VP8 Encoding Naivete

  15 octobre 2010, par Multimedia Mike — VP8

  I’ve been toiling away as a multimedia technology generalist for so long that it’s easy for me to forget that not everyone is as versed in the minutiae of the domain as I am. But I recently experienced what it’s like to be such an outsider when I posted about my toy VP8 encoder, expressing that it’s one of the hardest things I have ever tried to do. I heard of from number of people who do have extensive experience in video encoding, particularly with the H.264 and VP8 codecs. Their reactions were predictable : What’s so hard ? Look, you might be a little too immersed in the area to really understand a relative beginner’s perspective.

  And to all the people who suggested that I should get the encoder into FFmpeg ASAP : Are you crazy ?! Did you see what the first pass of the encoder produced ? Do you have lower standards than even I do ?

  
  
  

  Not Giving Up
  I worked a little more on the toy encoder. Remember that the above image is what I’m hoping to encode somewhat faithfully for this experiment. In my first pass, I attempted vertical prediction for all planes. For my next pass, I forced the chroma planes to mid-level (which results in a greyscale image) and played with the 16×16 luma prediction modes. When implementing an extremely naive algorithm to decide which 16×16 prediction mode would be the best for a particular block, this is what the program produced :

  
  
  

  For fun, here is what the image encodes to when forcing various prediction modes :
  

  I think the DC-only prediction mode actually looks a little better than the image that the naive algorithm produced :

  
  
  

  Vertical 16×16 prediction, similar to the image from the last post (just in black and white) :
  

  
  
  

  Horizontal 16×16 prediction :
  

  
  
  

  This is the 16×16 prediction mode unique to VP8, the TrueMotion mode (based on On2/Duck’s very first video codec) :
  

  
  
  

  Wow, these encodings really bring down the cheerful tone of the original image.

  Next Steps
  I have little reason to believe that I am encoding and subsequently reconstructing the image correctly (i.e., error is likely propagating through the entire encoding). If I have time, the next step is to validate my reconstruction against the encoder. Then I need to get the entropy considerations correct so that I actually get some compression out of this format.