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• swresample/resample : speed up upsampling by precomputing sines

  9 novembre 2015, par Ganesh Ajjanagadde

  swresample/resample : speed up upsampling by precomputing sines
  When upsampling, factor is set to 1 and sines need to be evaluated only
  
  once for each phase, and the complexity should not depend on the number
  
  of filter taps. This does the desired precomputation, yielding
  
  significant speedups. Hard guarantees on the gain are not possible, but gains
  
  themselves are obvious and are illustrated below.
  Sample benchmark (x86-64, Haswell, GNU/Linux)
  
  test : fate-swr-resample-dblp-2626-44100
  
  old :
  
  29161085 decicycles in build_filter (loop 1000),     256 runs,      0 skips
  
  28821467 decicycles in build_filter (loop 1000),     512 runs,      0 skips
  
  28668201 decicycles in build_filter (loop 1000),    1000 runs,     24 skips
  new :
  
  14351936 decicycles in build_filter (loop 1000),     256 runs,      0 skips
  
  14306652 decicycles in build_filter (loop 1000),     512 runs,      0 skips
  
  14299923 decicycles in build_filter (loop 1000),    1000 runs,     24 skips
  Note that this does not statically allocate the sin lookup table. This
  
  may be done for the default 1024 phases, yielding a 512*8 = 4kB array
  
  which should be small enough.
  
  This should yield a small improvement. Nevertheless, this is separate from
  
  this patch, is more ambiguous due to the binary increase, and requires a
  
  lut to be generated offline.
  Reviewed-by : Michael Niedermayer <michael@niedermayer.cc>
  
  Signed-off-by : Ganesh Ajjanagadde <gajjanagadde@gmail.com>
  

  • [DH] libswresample/resample.c

• vulkan_decode : remove informative queries

  24 décembre 2024, par Lynne

  vulkan_decode : remove informative queries
  We queried the decoder whether it was able to decode sucessfully, but
  
  since we operated asynchronously, we weren't able to do anything with
  
  this information but let the user know decoding failed for the previous
  
  frame(s).
  Since we parse the slice headers ourselves and we're reasonably sure we
  
  can decode before actually starting to decode, this was rarely triggered
  
  on corrupt data, and hardware's understanding of whether there was an error
  
  or not is vague.
  There's also a semantic problem with our use of the queries - if there's
  
  a seek, we flush, but what happens to the queries is vague according to
  
  the spec. Most hardware dealt fine, since queries are nothing more than
  
  GPU memory with integers stored. But with Intel, they seem to be more of
  
  a register to which a driver must keep track of, leading to issues if there's
  
  been a reset (seek) and we query the previous submission before the seek.
  Just get rid of them. The query code is still used in encoding.
  This fixes seeking with HEVC and AV1 on Intel.
  

  • [DH] libavcodec/vulkan_decode.c

• Segmentation fault in samplerate conversion function

  17 juin 2014, par user3749290

  playmp3() using libmpg123

  if (isPaused==0 && mpg123_read(mh, buffer, buffer_size, &done) == MPG123_OK)
  
  {
  
      char * resBuffer=&buffer[0]; //22100=0,5s
  
      buffer = resample(resBuffer,22100,22100);
  
      if((ao_play(dev, (char*)buffer, done)==0)){
  
          return 1;
  
  }

  resample() Using avcodec from ffmpeg

  #define LENGTH_MS 500       // how many milliseconds of speech to store
  
  #define RATE 44100      // the sampling rate (input)
  
  #define FORMAT PA_SAMPLE_S16NE  // sample size: 8 or 16 bits
  
  #define CHANNELS 2      // 1 = mono 2 = stereo
  
  
  
  struct AVResampleContext* audio_cntx = 0;
  
  
  
  char * resample(char in_buffer[(LENGTH_MS*RATE*16*CHANNELS)/8000],int out_rate,int nsamples)
  
  {
  
      char out_buffer[ sizeof( in_buffer ) * 4];
  
      audio_cntx = av_resample_init( out_rate, //out rate
  
          RATE, //in rate
  
          16, //filter length
  
          10, //phase count
  
          0, //linear FIR filter
  
          1.0 ); //cutoff frequency
  
      assert( audio_cntx && "Failed to create resampling context!");
  
      int samples_consumed;
  
      int samples_output = av_resample( audio_cntx, //resample context
  
          (short*)out_buffer, //buffout
  
          (short*)in_buffer,  //buffin
  
          &samples_consumed,  //&consumed
  
          nsamples,       //nb_samples
  
          sizeof(out_buffer)/2,//lenout
  
          0);//is_last
  
      assert( samples_output > 0 && "Error calling av_resample()!" );
  
      av_resample_close( audio_cntx );
  
      //*resample = malloc(sizeof(out_buffer));
  
      return &out_buffer[0];  
  
  }

  When i run this code i get 3393 Segmentation fault (core dump created). Why ?

  For example, the use of pointers is correct ?
  and 22100 are the samples that are contained in 0.5 seconds of the song ?