Optionally do not delay the first frame

A delay buffer delayed all the frames except the first one, to open the
scrcpy window immediately and get a picture.

Make this feature optional, so that the delay buffer might also be used
for audio (especially for simulating a high delay for debugging).

PR #3757 <https://github.com/Genymobile/scrcpy/pull/3757>

app/src/delay_buffer.c

@@ -194,10 +194,8 @@ sc_delay_buffer_frame_sink_push(struct sc_frame_sink *sink,
     sc_clock_update(&db->clock, sc_tick_now(), pts);
     sc_cond_signal(&db->wait_cond);
 
-    if (db->clock.count == 1) {
+    if (db->first_frame_asap && db->clock.count == 1) {
         sc_mutex_unlock(&db->mutex);
-        // First frame, push it immediately, not to delay the opening of the
-        // scrcpy window
         return sc_frame_source_sinks_push(&db->frame_source, frame);
     }
 
@@ -227,10 +225,12 @@ sc_delay_buffer_frame_sink_push(struct sc_frame_sink *sink,
 }
 
 void
-sc_delay_buffer_init(struct sc_delay_buffer *db, sc_tick delay) {
+sc_delay_buffer_init(struct sc_delay_buffer *db, sc_tick delay,
+                     bool first_frame_asap) {
     assert(delay > 0);
 
     db->delay = delay;
+    db->first_frame_asap = first_frame_asap;
 
     sc_frame_source_init(&db->frame_source);
 

app/src/delay_buffer.h

@@ -29,6 +29,7 @@ struct sc_delay_buffer {
     struct sc_frame_sink frame_sink; // frame sink trait
 
     sc_tick delay;
+    bool first_frame_asap;
 
     sc_thread thread;
     sc_mutex mutex;
@@ -49,8 +50,11 @@ struct sc_delay_buffer_callbacks {
  * Initialize a delay buffer.
  *
  * \param delay a (strictly) positive delay
+ * \param first_frame_asap if true, do not delay the first frame (useful for
+                           a video stream).
  */
 void
-sc_delay_buffer_init(struct sc_delay_buffer *db, sc_tick delay);
+sc_delay_buffer_init(struct sc_delay_buffer *db, sc_tick delay,
+                     bool first_frame_asap);
 
 #endif

app/src/scrcpy.c

@@ -669,7 +669,8 @@ aoa_hid_end:
 
         struct sc_frame_source *src = &s->video_decoder.frame_source;
         if (options->display_buffer) {
-            sc_delay_buffer_init(&s->display_buffer, options->display_buffer);
+            sc_delay_buffer_init(&s->display_buffer, options->display_buffer,
+                                 true);
             sc_frame_source_add_sink(src, &s->display_buffer.frame_sink);
             src = &s->display_buffer.frame_source;
         }
@@ -686,7 +687,7 @@ aoa_hid_end:
 
         struct sc_frame_source *src = &s->video_decoder.frame_source;
         if (options->v4l2_buffer) {
-            sc_delay_buffer_init(&s->v4l2_buffer, options->v4l2_buffer);
+            sc_delay_buffer_init(&s->v4l2_buffer, options->v4l2_buffer, true);
             sc_frame_source_add_sink(src, &s->v4l2_buffer.frame_sink);
             src = &s->v4l2_buffer.frame_source;
         }