Notify new frames via callbacks

Currently, a frame is available to the consumer as soon as it is pushed
by the producer (which can detect if the previous frame is skipped).

Notify the new frames (and frame skipped) via callbacks instead.

This paves the way to add (optional) buffering, which will introduce a
delay between the time when the frame is produced and the time it is
available to be consumed.

app/src/screen.c

@@ -274,14 +274,16 @@ screen_frame_sink_close(struct sc_frame_sink *sink) {
 static bool
 screen_frame_sink_push(struct sc_frame_sink *sink, const AVFrame *frame) {
     struct screen *screen = DOWNCAST(sink);
+    return sc_video_buffer_push(&screen->vb, frame);
+}
 
-    bool previous_frame_skipped;
-    bool ok = sc_video_buffer_push(&screen->vb, frame, &previous_frame_skipped);
-    if (!ok) {
-        return false;
-    }
+static void
+sc_video_buffer_on_new_frame(struct sc_video_buffer *vb, bool previous_skipped,
+                             void *userdata) {
+    (void) vb;
+    struct screen *screen = userdata;
 
-    if (previous_frame_skipped) {
+    if (previous_skipped) {
         fps_counter_add_skipped_frame(&screen->fps_counter);
         // The EVENT_NEW_FRAME triggered for the previous frame will consume
         // this new frame instead
@@ -293,8 +295,6 @@ screen_frame_sink_push(struct sc_frame_sink *sink, const AVFrame *frame) {
         // Post the event on the UI thread
         SDL_PushEvent(&new_frame_event);
     }
-
-    return true;
 }
 
 bool
@@ -304,7 +304,11 @@ screen_init(struct screen *screen, const struct screen_params *params) {
     screen->fullscreen = false;
     screen->maximized = false;
 
-    bool ok = sc_video_buffer_init(&screen->vb);
+    static const struct sc_video_buffer_callbacks cbs = {
+        .on_new_frame = sc_video_buffer_on_new_frame,
+    };
+
+    bool ok = sc_video_buffer_init(&screen->vb, &cbs, screen);
     if (!ok) {
         LOGE("Could not initialize video buffer");
         return false;

app/src/v4l2_sink.c

@@ -139,9 +139,27 @@ run_v4l2_sink(void *data) {
     return 0;
 }
 
+static void
+sc_video_buffer_on_new_frame(struct sc_video_buffer *vb, bool previous_skipped,
+                             void *userdata) {
+    (void) vb;
+    struct sc_v4l2_sink *vs = userdata;
+
+    if (!previous_skipped) {
+        sc_mutex_lock(&vs->mutex);
+        vs->has_frame = true;
+        sc_cond_signal(&vs->cond);
+        sc_mutex_unlock(&vs->mutex);
+    }
+}
+
 static bool
 sc_v4l2_sink_open(struct sc_v4l2_sink *vs) {
-    bool ok = sc_video_buffer_init(&vs->vb);
+    static const struct sc_video_buffer_callbacks cbs = {
+        .on_new_frame = sc_video_buffer_on_new_frame,
+    };
+
+    bool ok = sc_video_buffer_init(&vs->vb, &cbs, vs);
     if (!ok) {
         LOGE("Could not initialize video buffer");
         return false;
@@ -303,20 +321,7 @@ sc_v4l2_sink_close(struct sc_v4l2_sink *vs) {
 
 static bool
 sc_v4l2_sink_push(struct sc_v4l2_sink *vs, const AVFrame *frame) {
-    bool previous_skipped;
-    bool ok = sc_video_buffer_push(&vs->vb, frame, &previous_skipped);
-    if (!ok) {
-        return false;
-    }
-
-    if (!previous_skipped) {
-        sc_mutex_lock(&vs->mutex);
-        vs->has_frame = true;
-        sc_cond_signal(&vs->cond);
-        sc_mutex_unlock(&vs->mutex);
-    }
-
-    return true;
+    return sc_video_buffer_push(&vs->vb, frame);
 }
 
 static bool

app/src/video_buffer.c

@@ -7,8 +7,20 @@
 #include "util/log.h"
 
 bool
-sc_video_buffer_init(struct sc_video_buffer *vb) {
-    return sc_frame_buffer_init(&vb->fb);
+sc_video_buffer_init(struct sc_video_buffer *vb,
+                     const struct sc_video_buffer_callbacks *cbs,
+                     void *cbs_userdata) {
+    bool ok = sc_frame_buffer_init(&vb->fb);
+    if (!ok) {
+        return false;
+    }
+
+    assert(cbs);
+    assert(cbs->on_new_frame);
+
+    vb->cbs = cbs;
+    vb->cbs_userdata = cbs_userdata;
+    return true;
 }
 
 void
@@ -17,9 +29,15 @@ sc_video_buffer_destroy(struct sc_video_buffer *vb) {
 }
 
 bool
-sc_video_buffer_push(struct sc_video_buffer *vb, const AVFrame *frame,
-                  bool *previous_frame_skipped) {
-    return sc_frame_buffer_push(&vb->fb, frame, previous_frame_skipped);
+sc_video_buffer_push(struct sc_video_buffer *vb, const AVFrame *frame) {
+    bool previous_skipped;
+    bool ok = sc_frame_buffer_push(&vb->fb, frame, &previous_skipped);
+    if (!ok) {
+        return false;
+    }
+
+    vb->cbs->on_new_frame(vb, previous_skipped, vb->cbs_userdata);
+    return true;
 }
 
 void

app/src/video_buffer.h

@@ -12,17 +12,26 @@ typedef struct AVFrame AVFrame;
 
 struct sc_video_buffer {
     struct sc_frame_buffer fb;
+
+    const struct sc_video_buffer_callbacks *cbs;
+    void *cbs_userdata;
+};
+
+struct sc_video_buffer_callbacks {
+    void (*on_new_frame)(struct sc_video_buffer *vb, bool previous_skipped,
+                         void *userdata);
 };
 
 bool
-sc_video_buffer_init(struct sc_video_buffer *vb);
+sc_video_buffer_init(struct sc_video_buffer *vb,
+                     const struct sc_video_buffer_callbacks *cbs,
+                     void *cbs_userdata);
 
 void
 sc_video_buffer_destroy(struct sc_video_buffer *vb);
 
 bool
-sc_video_buffer_push(struct sc_video_buffer *vb, const AVFrame *frame,
-                     bool *skipped);
+sc_video_buffer_push(struct sc_video_buffer *vb, const AVFrame *frame);
 
 void
 sc_video_buffer_consume(struct sc_video_buffer *vb, AVFrame *dst);