Method ProcessOne

libraries/lib-builtin-effects/ChangeSpeedBase.cpp:238–293

ProcessOne() takes a track, transforms it to bunch of buffer-blocks, and calls libsamplerate code on these blocks.

// ProcessOne() takes a track, transforms it to bunch of buffer-blocks,
// and calls libsamplerate code on these blocks.
bool ChangeSpeedBase::ProcessOne(
   const WaveChannel& track, WaveChannel& outputTrack, sampleCount start,
   sampleCount end)
{
   // Get the length of the selection (as double). len is
   // used simple to calculate a progress meter, so it is easier
   // to make it a double now than it is to do it later
   auto len = (end - start).as_double();

   // Initiate processing buffers, most likely shorter than
   // the length of the selection being processed.
   auto inBufferSize = track.GetMaxBlockSize();

   Floats inBuffer { inBufferSize };

   // mFactor is at most 100-fold so this shouldn't overflow size_t
   auto outBufferSize = size_t(mFactor * inBufferSize + 10);
   Floats outBuffer { outBufferSize };

   // Set up the resampling stuff for this track.
   Resample resample(true, mFactor, mFactor); // constant rate resampling

   // Go through the track one buffer at a time. samplePos counts which
   // sample the current buffer starts at.
   bool bResult = true;
   auto samplePos = start;
   while (samplePos < end)
   {
      // Get a blockSize of samples (smaller than the size of the buffer)
      auto blockSize = limitSampleBufferSize(
         track.GetBestBlockSize(samplePos), end - samplePos);

      // Get the samples from the track and put them in the buffer
      track.GetFloats(inBuffer.get(), samplePos, blockSize);

      const auto results = resample.Process(
         mFactor, inBuffer.get(), blockSize, ((samplePos + blockSize) >= end),
         outBuffer.get(), outBufferSize);
      const auto outgen = results.second;

      if (outgen > 0)
         outputTrack.Append((samplePtr)outBuffer.get(), floatSample, outgen);

      // Increment samplePos
      samplePos += results.first;

      // Update the Progress meter
      if (TrackProgress(mCurTrackNum, (samplePos - start).as_double() / len))
      {
         bResult = false;
         break;
      }
   }

   return bResult;
}