swresample: add exact_rational option

give high quality resampling
as good as with linear_interp=on
as fast as without linear_interp=on
tested visually with ffplay
ffplay -f lavfi "aevalsrc='sin(10000*t*t)', aresample=osr=48000, showcqt=gamma=5"
ffplay -f lavfi "aevalsrc='sin(10000*t*t)', aresample=osr=48000:linear_interp=on, showcqt=gamma=5"
ffplay -f lavfi "aevalsrc='sin(10000*t*t)', aresample=osr=48000:exact_rational=on, showcqt=gamma=5"

slightly speed improvement
for fair comparison with -cpuflags 0
audio.wav is ~ 1 hour 44100 stereo 16bit wav file
ffmpeg -i audio.wav -af aresample=osr=48000 -f null -
        old         new
real    13.498s     13.121s
user    13.364s     12.987s
sys      0.131s      0.129s

linear_interp=on
        old         new
real    23.035s     23.050s
user    22.907s     22.917s
sys      0.119s     0.125s

exact_rational=on
real    12.418s
user    12.298s
sys      0.114s

possibility to decrease memory usage if soft compensation is ignored

Signed-off-by: Muhammad Faiz <mfcc64@gmail.com>

1 files changed, 22 insertions, 8 deletions

diff --git a/libswresample/resample_template.c b/libswresample/resample_template.c
index d71efd63c0..1636f4e95d 100644
--- a/libswresample/resample_template.c
+++ b/libswresample/resample_template.c
@@ -92,9 +92,13 @@ static int RENAME(resample_common)(ResampleContext *c,
     int dst_index;
     int index= c->index;
     int frac= c->frac;
-    int sample_index = index >> c->phase_shift;
+    int sample_index = 0;
+
+    while (index >= c->phase_count) {
+        sample_index++;
+        index -= c->phase_count;
+    }
 
-    index &= c->phase_mask;
     for (dst_index = 0; dst_index < n; dst_index++) {
         FELEM *filter = ((FELEM *) c->filter_bank) + c->filter_alloc * index;
 
@@ -111,8 +115,11 @@ static int RENAME(resample_common)(ResampleContext *c,
             frac -= c->src_incr;
             index++;
         }
-        sample_index += index >> c->phase_shift;
-        index &= c->phase_mask;
+
+        while (index >= c->phase_count) {
+            sample_index++;
+            index -= c->phase_count;
+        }
     }
 
     if(update_ctx){
@@ -132,12 +139,16 @@ static int RENAME(resample_linear)(ResampleContext *c,
     int dst_index;
     int index= c->index;
     int frac= c->frac;
-    int sample_index = index >> c->phase_shift;
+    int sample_index = 0;
 #if FILTER_SHIFT == 0
     double inv_src_incr = 1.0 / c->src_incr;
 #endif
 
-    index &= c->phase_mask;
+    while (index >= c->phase_count) {
+        sample_index++;
+        index -= c->phase_count;
+    }
+
     for (dst_index = 0; dst_index < n; dst_index++) {
         FELEM *filter = ((FELEM *) c->filter_bank) + c->filter_alloc * index;
         FELEM2 val=0, v2 = 0;
@@ -164,8 +175,11 @@ static int RENAME(resample_linear)(ResampleContext *c,
             frac -= c->src_incr;
             index++;
         }
-        sample_index += index >> c->phase_shift;
-        index &= c->phase_mask;
+
+        while (index >= c->phase_count) {
+            sample_index++;
+            index -= c->phase_count;
+        }
     }
 
     if(update_ctx){