echo-cancel: Do not bypass EC implementation when play stream is empty

When the play stream from the EC sink has not enough data available then
the EC implementation is currently bypassed by directly forwarding the
record bytes to the EC source. Since EC implementations maintain their
own buffers and cause certain latencies, a bypass leads to glitches as
the out stream stream jumps forth and back in time. Furthermore, some
EC implementations may also apply noise reduction or other sound
enhancing techniques, which are therefore bypassed, too.

Fix this by passing silence bytes to the EC implementation if the play
stream runs empty. Hence, this patch keeps the EC implementation running
even if the play stream has no data available.

diff --git a/src/modules/echo-cancel/module-echo-cancel.c b/src/modules/echo-cancel/module-echo-cancel.c
index 9d94a83..1e9af37 100644 (file)
--- a/src/modules/echo-cancel/module-echo-cancel.c
+++ b/src/modules/echo-cancel/module-echo-cancel.c
@@ -820,60 +820,61 @@ static void do_push(struct userdata *u) {
     plen = pa_memblockq_get_length(u->sink_memblockq);
 
     while (rlen >= u->source_blocksize) {
-        /* take fixed block from recorded samples */
-        pa_memblockq_peek_fixed_size(u->source_memblockq, u->source_blocksize, &rchunk);
 
-        if (plen >= u->sink_blocksize) {
-            /* take fixed block from played samples */
-            pa_memblockq_peek_fixed_size(u->sink_memblockq, u->sink_blocksize, &pchunk);
-
-            rdata = pa_memblock_acquire(rchunk.memblock);
-            rdata += rchunk.index;
-            pdata = pa_memblock_acquire(pchunk.memblock);
-            pdata += pchunk.index;
-
-            cchunk.index = 0;
-            cchunk.length = u->source_blocksize;
-            cchunk.memblock = pa_memblock_new(u->source->core->mempool, cchunk.length);
-            cdata = pa_memblock_acquire(cchunk.memblock);
-
-            if (u->save_aec) {
-                if (u->captured_file)
-                    unused = fwrite(rdata, 1, u->source_blocksize, u->captured_file);
-                if (u->played_file)
-                    unused = fwrite(pdata, 1, u->sink_blocksize, u->played_file);
-            }
+        /* take fixed blocks from recorded and played samples */
+        pa_memblockq_peek_fixed_size(u->source_memblockq, u->source_blocksize, &rchunk);
+        pa_memblockq_peek_fixed_size(u->sink_memblockq, u->sink_blocksize, &pchunk);
 
-            /* perform echo cancellation */
-            u->ec->run(u->ec, rdata, pdata, cdata);
+        /* we ran out of played data and pchunk has been filled with silence bytes */
+        if (plen < u->sink_blocksize)
+            pa_memblockq_seek(u->sink_memblockq, u->sink_blocksize - plen, PA_SEEK_RELATIVE, true);
 
-            if (u->save_aec) {
-                if (u->canceled_file)
-                    unused = fwrite(cdata, 1, u->source_blocksize, u->canceled_file);
-            }
+        rdata = pa_memblock_acquire(rchunk.memblock);
+        rdata += rchunk.index;
+        pdata = pa_memblock_acquire(pchunk.memblock);
+        pdata += pchunk.index;
 
-            pa_memblock_release(cchunk.memblock);
-            pa_memblock_release(pchunk.memblock);
-            pa_memblock_release(rchunk.memblock);
+        cchunk.index = 0;
+        cchunk.length = u->source_blocksize;
+        cchunk.memblock = pa_memblock_new(u->source->core->mempool, cchunk.length);
+        cdata = pa_memblock_acquire(cchunk.memblock);
 
-            /* drop consumed sink samples */
-            pa_memblockq_drop(u->sink_memblockq, u->sink_blocksize);
-            pa_memblock_unref(pchunk.memblock);
+        if (u->save_aec) {
+            if (u->captured_file)
+                unused = fwrite(rdata, 1, u->source_blocksize, u->captured_file);
+            if (u->played_file)
+                unused = fwrite(pdata, 1, u->sink_blocksize, u->played_file);
+        }
 
-            pa_memblock_unref(rchunk.memblock);
-            /* the filtered samples now become the samples from our
-             * source */
-            rchunk = cchunk;
+        /* perform echo cancellation */
+        u->ec->run(u->ec, rdata, pdata, cdata);
 
-            plen -= u->sink_blocksize;
+        if (u->save_aec) {
+            if (u->canceled_file)
+                unused = fwrite(cdata, 1, u->source_blocksize, u->canceled_file);
         }
 
-        /* forward the (echo-canceled) data to the virtual source */
-        pa_source_post(u->source, &rchunk);
-        pa_memblock_unref(rchunk.memblock);
+        pa_memblock_release(cchunk.memblock);
+        pa_memblock_release(pchunk.memblock);
+        pa_memblock_release(rchunk.memblock);
 
+        /* drop consumed source samples */
         pa_memblockq_drop(u->source_memblockq, u->source_blocksize);
+        pa_memblock_unref(rchunk.memblock);
         rlen -= u->source_blocksize;
+
+        /* drop consumed sink samples */
+        pa_memblockq_drop(u->sink_memblockq, u->sink_blocksize);
+        pa_memblock_unref(pchunk.memblock);
+
+        if (plen >= u->sink_blocksize)
+            plen -= u->sink_blocksize;
+        else
+            plen = 0;
+
+        /* forward the (echo-canceled) data to the virtual source */
+        pa_source_post(u->source, &cchunk);
+        pa_memblock_unref(cchunk.memblock);
     }
 }
 
@@ -1940,7 +1941,7 @@ int pa__init(pa_module*m) {
     u->source_memblockq = pa_memblockq_new("module-echo-cancel source_memblockq", 0, MEMBLOCKQ_MAXLENGTH, 0,
         &source_ss, 1, 1, 0, &silence);
     u->sink_memblockq = pa_memblockq_new("module-echo-cancel sink_memblockq", 0, MEMBLOCKQ_MAXLENGTH, 0,
-        &sink_ss, 1, 1, 0, &silence);
+        &sink_ss, 0, 1, 0, &silence);
 
     pa_memblock_unref(silence.memblock);