Use a callback to notify a new frame

Make the decoder independant of the SDL even mechanism, by registering a
callback on the video_buffer.

app/src/decoder.c

@@ -19,13 +19,7 @@ push_frame(struct decoder *decoder) {
                                       &previous_frame_skipped);
     if (previous_frame_skipped) {
         fps_counter_add_skipped_frame(decoder->fps_counter);
-        // the previous EVENT_NEW_FRAME will consume this frame
-        return;
     }
-    static SDL_Event new_frame_event = {
-        .type = EVENT_NEW_FRAME,
-    };
-    SDL_PushEvent(&new_frame_event);
 }
 
 void

app/src/scrcpy.c

@@ -267,6 +267,19 @@ av_log_callback(void *avcl, int level, const char *fmt, va_list vl) {
     free(local_fmt);
 }
 
+static void
+video_buffer_on_frame_available(struct video_buffer *vb, void *userdata) {
+    (void) vb;
+    (void) userdata;
+
+    static SDL_Event new_frame_event = {
+        .type = EVENT_NEW_FRAME,
+    };
+
+    // Post the event on the UI thread
+    SDL_PushEvent(&new_frame_event);
+}
+
 bool
 scrcpy(const struct scrcpy_options *options) {
     if (!server_init(&server)) {
@@ -333,7 +346,12 @@ scrcpy(const struct scrcpy_options *options) {
         }
         fps_counter_initialized = true;
 
-        if (!video_buffer_init(&video_buffer, options->render_expired_frames)) {
+        static const struct video_buffer_callbacks video_buffer_cbs = {
+            .on_frame_available = video_buffer_on_frame_available,
+        };
+
+        if (!video_buffer_init(&video_buffer, options->render_expired_frames,
+                               &video_buffer_cbs, NULL)) {
             goto end;
         }
         video_buffer_initialized = true;

app/src/video_buffer.c

@@ -7,7 +7,9 @@
 #include "util/log.h"
 
 bool
-video_buffer_init(struct video_buffer *vb, bool wait_consumer) {
+video_buffer_init(struct video_buffer *vb, bool wait_consumer,
+                  const struct video_buffer_callbacks *cbs,
+                  void *cbs_userdata) {
     vb->producer_frame = av_frame_alloc();
     if (!vb->producer_frame) {
         goto error_0;
@@ -43,6 +45,11 @@ video_buffer_init(struct video_buffer *vb, bool wait_consumer) {
     // there is initially no frame, so consider it has already been consumed
     vb->pending_frame_consumed = true;
 
+    assert(cbs);
+    assert(cbs->on_frame_available);
+    vb->cbs = cbs;
+    vb->cbs_userdata = cbs_userdata;
+
     return true;
 
 error_3:
@@ -95,10 +102,17 @@ video_buffer_producer_offer_frame(struct video_buffer *vb,
 
     video_buffer_swap_producer_frame(vb);
 
-    *previous_frame_skipped = !vb->pending_frame_consumed;
+    bool skipped = !vb->pending_frame_consumed;
+    *previous_frame_skipped = skipped;
     vb->pending_frame_consumed = false;
 
     sc_mutex_unlock(&vb->mutex);
+
+    if (!skipped) {
+        // If skipped, then the previous call will consume this frame, the
+        // callback must not be called
+        vb->cbs->on_frame_available(vb, vb->cbs_userdata);
+    }
 }
 
 const AVFrame *

app/src/video_buffer.h

@@ -39,10 +39,20 @@ struct video_buffer {
 
     sc_cond pending_frame_consumed_cond;
     bool pending_frame_consumed;
+
+    const struct video_buffer_callbacks *cbs;
+    void *cbs_userdata;
+};
+
+struct video_buffer_callbacks {
+    // Called when a new frame can be consumed by
+    // video_buffer_consumer_take_frame(vb)
+    void (*on_frame_available)(struct video_buffer *vb, void *userdata);
 };
 
 bool
-video_buffer_init(struct video_buffer *vb, bool wait_consumer);
+video_buffer_init(struct video_buffer *vb, bool wait_consumer,
+                  const struct video_buffer_callbacks *cbs, void *cbs_userdata);
 
 void
 video_buffer_destroy(struct video_buffer *vb);