Changeset 495

Timestamp:

Jun 8, 2006 2:08:58 PM (18 years ago)

Author:

bennylp

Message:

Fixed bug in xoff calculation in PJMEDIA resample

File:

• pjproject/trunk/pjmedia/src/pjmedia/resample.c (modified) (6 diffs)

pjproject/trunk/pjmedia/src/pjmedia/resample.c

@@ -530 +530 @@
     resample->large_filter = large_filter;
     resample->high_quality = high_quality;
-    resample->xoff = large_filter ? 32 : 6;
     resample->frame_size = samples_per_frame;
 
@@ -537 +536 @@
         unsigned i;
 
+        /* This is a bug in xoff calculation, thanks Stephane Lussier
+         * of Macadamian dot com.
+         *   resample->xoff = large_filter ? 32 : 6;
+         */
+        if (large_filter)
+            resample->xoff = (LARGE_FILTER_NMULT + 1) / 2.0  *  
+                             MAX(1.0, 1.0/resample->factor);
+        else
+            resample->xoff = (SMALL_FILTER_NMULT + 1) / 2.0  *  
+                             MAX(1.0, 1.0/resample->factor);
+
+
         size = (samples_per_frame + 2*resample->xoff) * sizeof(pj_int16_t);
         resample->buffer = pj_pool_alloc(pool, size);
@@ -544 +555 @@
             resample->buffer[i] = 0;
         }
+
+
+    } else {
+        resample->xoff = 0;
     }
 
@@ -563 +578 @@
         const pj_int16_t *src_buf;
 
-        /* Buffer layout:
+        /* Okay chaps, here's how we do resampling.
+         *
+         * The original resample algorithm requires xoff samples *before* the
+         * input buffer as history, and another xoff samples *after* the
+         * end of the input buffer as lookahead. Since application can only
+         * supply framesize buffer on each run, PJMEDIA needs to arrange the
+         * buffer to meet these requirements.
+         *
+         * So here comes the trick.
+         *
+         * First of all, because of the history and lookahead requirement, 
+         * resample->buffer need to accomodate framesize+2*xoff samples in its
+         * buffer. This is done when the buffer is created.
+         *
+         * On the first run, the input frame (supplied by application) is
+         * copied to resample->buffer at 2*xoff position. The first 2*xoff
+         * samples are initially zeroed (in the initialization). The resample
+         * algorithm then invoked at resample->buffer+xoff ONLY, thus giving
+         * it one xoff at the beginning as zero, and one xoff at the end
+         * as the end of the original input. The resample algorithm will see
+         * that the first xoff samples in the input as zero.
+         *
+         * So here's the layout of resample->buffer on the first run.
          *
          * run 0 
@@ -572 +609 @@
          *     0    xoff  2*xoff       size+2*xoff 
          *
-         * run 01
+         * (Note again: resample algorithm is called at resample->buffer+xoff)
+         *
+         * At the end of the run, 2*xoff samples from the end of 
+         * resample->buffer are copied to the beginning of resample->buffer.
+         * The first xoff part of this will be used as history for the next
+         * run, and the second xoff part of this is actually the start of
+         * resampling for the next run.
+         *
+         * And the first run completes, the function returns.
+         *
+         * 
+         * On the next run, the input frame supplied by application is again
+         * copied at 2*xoff position in the resample->buffer, and the 
+         * resample algorithm is again invoked at resample->buffer+xoff 
+         * position. So effectively, the resample algorithm will start its
+         * operation on the last xoff from the previous frame, and gets the
+         * history from the last 2*xoff of the previous frame, and the look-
+         * ahead from the last xoff of current frame.
+         *
+         * So on this run, the buffer layout is:
+         *
+         * run 1
          *     +------+------+--------------+
          *     | frm0 | frm0 |  frame1...   |
@@ -578 +636 @@
          *     ^      ^      ^              ^
          *     0    xoff  2*xoff       size+2*xoff 
+         *
+         * As you can see from above diagram, the resampling algorithm is
+         * actually called from the last xoff part of previous frame (frm0).
+         *
+         * And so on the process continues for the next frame, and the next,
+         * and the next, ...
+         *
          */
         dst_buf = resample->buffer + resample->xoff*2;