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• Algorithm to draw waveform from audio

  25 septembre 2024, par yayuj

  I'm trying to draw a waveform from a raw audio file. I demuxed/decoded an audio file using FFmpeg and I have those informations : samples buffer, the size of the samples buffer, the duration of the audio file (in seconds), sample rate (44100, 48000, etc), sample size, sample format (uint8, int16, int32, float, double), and the raw audio data itself.

  



  Digging on the Internet I found this algorithm (more here) :

  



  White Noise :

  



  

  



  The Algorithm

  



  


  All you need to do is randomize every sample from –amplitude to
 amplitude. We don’t care about the number of channels in most cases so
 we just fill every sample with a new random number.

  


  



  Random rnd = new Random();
short randomValue = 0;

for (int i = 0; i < numSamples; i++)
{
    randomValue = Convert.ToInt16(rnd.Next(-amplitude, amplitude));
    data.shortArray[i] = randomValue;
}


  



  It's really good but I don't want to draw that way, but this way :

  



  

  



  Is there any algorithm or idea of how I can be drawing using the informations that I have ?

  


• intrax8 : Use local destination buffers

  20 février 2016, par Vittorio Giovara

  intrax8 : Use local destination buffers
  These buffers are just a way to store frame pointers and be able to
  
  modify them without touching the original ones.
  The two dependent decoders (WMV2 and VC1) do not need special care for
  
  these fields : the former does not seem to use the dest buffers, while
  
  the latter reinits them every time to the current frame data buffers.
  So only keep a local copy rather than the one from mpegvideo.
  

  • [DBH] libavcodec/intrax8.c
  • [DBH] libavcodec/intrax8.h

• FFMPEG : Explain parameters of any codecs function pointers

  7 juillet 2014, par Zax

  I’m going through the article, How to integrate a codec in FFMPEG multimedia framework.
  According to it, every codec needs to have 3 basic functions to be defined and these functions are assigned to function pointers of the structure AVCodec.

  The 3 function pointers specified in the above article are :

  .init -> takes care of allocations and other initializations
  
  
  
  .close -> freeing the allocated memory and de-initializations
  
  
  
  .decode -> frame by frame decoding.

  For the function pointer .decode, the function assigned is :

  static int cook_decode_frame(AVCodecContext *avctx,
  
              void *data, int *data_size,
  
              uint8_t *buf, int buf_size) {
  
  ...

  The details of these parameters are specified in the above article. However, in the latest code, when the same function is taken as an example, its declaration is as shown below :

  static int cook_decode_frame(AVCodecContext *avctx, void *data,
  
                               int *got_frame_ptr, AVPacket *avpkt)

  I need to perform some mapping operations on the memory. So, i request if anyone could kindly explain the above parameters in the function declarations. Also, which parameter has the input buffer for decoding the frame ? And after decoding a frame, to which parameter is the decoded frame mapped ?