shithub: audio-stretch

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improve speed of "fast" mode (when stretch > 1.5X) by fully consuming each period pair

- note that this can generate more output for each call, so might require client change
- may slightly reduce subjective quality, so use "normal" mode if that's paramount

--- a/main.c

+++ b/main.c

@@ -338,7 +338,7 @@

     write_pcm_wav_header (outfile, 0, WaveHeader.NumChannels, 2, scaled_rate);

     short *inbuffer = malloc (BUFFER_SAMPLES * WaveHeader.BlockAlign);

-    short *outbuffer = malloc ((BUFFER_SAMPLES * 2 + max_period * 3) * WaveHeader.BlockAlign);

+    short *outbuffer = malloc ((BUFFER_SAMPLES * 2 + max_period * 4) * WaveHeader.BlockAlign);

     while (1) {

         int samples_read = fread (inbuffer, WaveHeader.BlockAlign,

--- a/stretch.c

+++ b/stretch.c

@@ -98,8 +98,8 @@

  * range 0.5 to 2.0). Note that the number of samples refers to total samples for

  * both channels in stereo and can be as large as desired (samples are buffered

  * here). The exact number of samples output is not possible to determine in

- * advance, but it will be close to the number of input samples times the ratio

- * plus or minus 3X the longest period.

+ * advance, but the maximum will be the number of input samples times the ratio

+ * plus 3X the longest period (or 4X the longest period in "fast" mode).

  */

 int stretch_samples (StretchHandle handle, const short *samples, int num_samples, short *output, float ratio)

@@ -133,7 +133,7 @@

         /* while there are enough samples to process, do so */

-        while (cnxt->tail >= cnxt->longest && cnxt->head - cnxt->tail >= cnxt->longest * 2) {

+        while (cnxt->tail >= cnxt->longest && cnxt->head - cnxt->tail >= cnxt->longest * (cnxt->fast_mode ? 3 : 2)) {

             int period = cnxt->fast_mode ? find_period_fast (cnxt, cnxt->inbuff + cnxt->tail) :

                 find_period (cnxt, cnxt->inbuff + cnxt->tail);

             float process_ratio;

@@ -183,6 +183,15 @@

                 cnxt->outsamples_error += (period * 2.0) - (period * ratio);

                 out_samples += period * 2;

                 cnxt->tail += period;

+

+                if (cnxt->fast_mode) {

+                    merge_blocks (output + out_samples, cnxt->inbuff + cnxt->tail,

+                        cnxt->inbuff + cnxt->tail - period, period * 2);

+

+                    cnxt->outsamples_error += (period * 2.0) - (period * ratio);

+                    out_samples += period * 2;

+                    cnxt->tail += period;

+                }

             }

             else

                 fprintf (stderr, "stretch_samples: fatal programming error: process_ratio == %g\n", process_ratio);