audio: avoid unnecessary silence padding in read_buffer()

Not all callers of read_buffer() require the buffer to be padded with
silence.

audio/out/buffer.c

@@ -114,7 +114,8 @@ struct mp_async_queue *ao_get_queue(struct ao *ao)
 }
 
 // Special behavior with data==NULL: caller uses p->pending.
-static int read_buffer(struct ao *ao, void **data, int samples, bool *eof)
+static int read_buffer(struct ao *ao, void **data, int samples, bool *eof,
+                       bool pad_silence)
 {
     struct buffer_state *p = ao->buffer_state;
     int pos = 0;
@@ -160,23 +161,25 @@ static int read_buffer(struct ao *ao, void **data, int samples, bool *eof)
     }
 
     // pad with silence (underflow/paused/eof)
-    for (int n = 0; n < ao->num_planes; n++) {
-        af_fill_silence((char *)data[n] + pos * ao->sstride,
-                        (samples - pos) * ao->sstride,
-                        ao->format);
+    if (pad_silence) {
+        for (int n = 0; n < ao->num_planes; n++) {
+            af_fill_silence((char *)data[n] + pos * ao->sstride,
+                    (samples - pos) * ao->sstride,
+                    ao->format);
+        }
     }
 
     ao_post_process_data(ao, data, pos);
     return pos;
 }
 
 static int ao_read_data_unlocked(struct ao *ao, void **data, int samples,
-                                 int64_t out_time_ns)
+                                 int64_t out_time_ns, bool pad_silence)
 {
     struct buffer_state *p = ao->buffer_state;
     assert(!ao->driver->write);
 
-    int pos = read_buffer(ao, data, samples, &(bool){0});
+    int pos = read_buffer(ao, data, samples, &(bool){0}, pad_silence);
 
     if (pos > 0)
         p->end_time_ns = out_time_ns;
@@ -205,7 +208,7 @@ int ao_read_data(struct ao *ao, void **data, int samples, int64_t out_time_ns)
 
     mp_mutex_lock(&p->lock);
 
-    int pos = ao_read_data_unlocked(ao, data, samples, out_time_ns);
+    int pos = ao_read_data_unlocked(ao, data, samples, out_time_ns, true);
 
     mp_mutex_unlock(&p->lock);
 
@@ -221,7 +224,7 @@ int ao_read_data_nonblocking(struct ao *ao, void **data, int samples, int64_t ou
     if (mp_mutex_trylock(&p->lock))
             return 0;
 
-    int pos = ao_read_data_unlocked(ao, data, samples, out_time_ns);
+    int pos = ao_read_data_unlocked(ao, data, samples, out_time_ns, false);
 
     mp_mutex_unlock(&p->lock);
 
@@ -623,7 +626,7 @@ static bool ao_play_data(struct ao *ao)
     bool got_eof = false;
     if (ao->driver->write_frames) {
         TA_FREEP(&p->pending);
-        samples = read_buffer(ao, NULL, 1, &got_eof);
+        samples = read_buffer(ao, NULL, 1, &got_eof, false);
         planes = (void **)&p->pending;
     } else {
         if (!realloc_buf(ao, space)) {
@@ -640,7 +643,7 @@ static bool ao_play_data(struct ao *ao)
         }
 
         if (!samples) {
-            samples = read_buffer(ao, planes, space, &got_eof);
+            samples = read_buffer(ao, planes, space, &got_eof, true);
             if (p->paused || (ao->stream_silence && !p->playing))
                 samples = space; // read_buffer() sets remainder to silent
         }