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• Port r17546 from Tremor ; although pieces had made it over to libvorbis, a comprehensive

  3 février 2012, par Monty

  Port r17546 from Tremor ; although pieces had made it over to libvorbis, a comprehensive
  port and verification was called for.  This patch provided some additional floor0
  hardening :
    floor0 code could potentially use a book where the number of vals it
  
    needed to decode was not an integer number of dims wide.  This caused
  
    it to overflow the output vector as the termination condition was in
  
    the outer loop of vorbis_book_decodev_set.
    None of the various vorbis_book_decodeXXXX calls internally guard
  
    against this case either, but in every other use the calling code does
  
    properly guard (and avoids putting more checks in the tight inner
  
    decode loop).
    For floor0, move the checks into the inner loop as there’s little
  
    penalty for doing so.
  [an equivalent change was already in libvorbis, but I’ve
  
  harmonized the code with tremor]
    For floor0, move the checks into the inner loop as there’s little
  
    penalty for doing so.  Add commentary indicating where guarding is
  
    done for each call variant.
  git-svn-id : http://svn.xiph.org/trunk/vorbis@18183 0101bb08-14d6-0310-b084-bc0e0c8e3800
  

  • [DH] lib/codebook.c
  • [DH] lib/floor0.c

• How To Write An Oscilloscope

  29 avril 2012, par Multimedia Mike — General, gme, oscilloscope, visualization

  I’m trying to figure out how to write a software oscilloscope audio visualization. It’s made more frustrating by the knowledge that I am certain that I have accomplished this task before.

  In this context, the oscilloscope is used to draw the time-domain samples of an audio wave form. I have written such a plugin as part of the xine project. However, for that project, I didn’t have to write the full playback pipeline— my plugin was just handed some PCM data and drew some graphical data in response. Now I’m trying to write the entire engine in a standalone program and I’m wondering how to get it just right.

  
  
  

  This is an SDL-based oscilloscope visualizer and audio player for Game Music Emu library. My approach is to have an audio buffer that holds a second of audio (44100 stereo 16-bit samples). The player updates the visualization at 30 frames per second. The o-scope is 512 pixels wide. So, at every 1/30th second interval, the player dips into the audio buffer at position ((frame_number % 30) * 44100 / 30) and takes the first 512 stereo frames for plotting on the graph.

  It seems to be working okay, I guess. The only problem is that the A/V sync seems to be slightly misaligned. I am just wondering if this is the correct approach. Perhaps the player should be performing some slightly more complicated calculation over those (44100/30) audio frames during each update in order to obtain a more accurate graph ? I described my process to an electrical engineer friend of mine and he insisted that I needed to apply something called hysteresis to the output or I would never get accurate A/V sync in this scenario.

  Further, I know that some schools of thought on these matters require that the dots in those graphs be connected, that the scattered points simply won’t do. I guess it’s a stylistic choice.

  Still, I think I have a reasonable, workable approach here. I might just be starting the visualization 1/30th of a second too late.

• FFmpeg - How to scale a video then apply a watermark ?

  28 août 2016, par Olibanum

  Im trying to scale a video so that it is always 512 wide where the height changes in proportion to the original video.
  Once scaled, I then want to apply a watermark/overlay to the video, therefore the video will scale but the watermark wont.

  I am able to achieve each of these separately using the following filters :

  Scale

  -vf "scale=512:-1"

  Watermark

  -vf "movie=watermark.png [watermark]; [in][watermark] overlay=(main_w-overlay_w)/2:(main_h-overlay_h)/2 [out]"

  They work successfully on their own.

  However when trying to combine the two, Im having a bit of trouble.

  Having both as parameters of course does not work as one will override the other.

  Ive tried :

  -vf "scale=512:-1,movie=watermark.png [watermark]; [in][watermark] overlay=(main_w-overlay_w)/2:(main_h-overlay_h)/2 [out]"

  my thinking was that the scale would be applied first then the watermark but all I get is an error

  Too many inputs specified for the "movie" filter.

  Error opening filters !

  Then changing the , to a ; resulted in :

  Simple filtergraph ’scale=512 :-1 ;
  movie=watermark.png
  [watermark] ; [in][watermark]
  overlay=(main_w-overlay_w)/2 :(main_h-overlay_h)/2 [out]’ does not have
  exactly one input and output.

  Error opening filters !

  I presume I need to do something more with filterchains but Im struggling to figure it out.

  Any ideas anyone ?

  Many thanks in advance.