Move producer/consumer frames out of video buffer

The video buffer held 3 frames:
 - the producer frame (for decoding)
 - the pending frame (to exchange between the producer and consumer)
 - the consumer frame (for rendering)

It worked well, but it prevented video buffers to be chained, because
the consumer frame of the first video buffer must be the same as the
producer frame of the second video buffer.

To solve this problem, make the decoder and the screen handle their own
frames, and keep only the pending frame in the video_buffer.

This paves the way to support asynchronous swscale.

app/src/decoder.c

@@ -30,11 +30,20 @@ decoder_open(struct decoder *decoder, const AVCodec *codec) {
         return false;
     }
 
+    decoder->frame = av_frame_alloc();
+    if (!decoder->frame) {
+        LOGE("Could not create decoder frame");
+        avcodec_close(decoder->codec_ctx);
+        avcodec_free_context(&decoder->codec_ctx);
+        return false;
+    }
+
     return true;
 }
 
 void
 decoder_close(struct decoder *decoder) {
+    av_frame_free(&decoder->frame);
     avcodec_close(decoder->codec_ctx);
     avcodec_free_context(&decoder->codec_ctx);
 }
@@ -49,11 +58,11 @@ decoder_push(struct decoder *decoder, const AVPacket *packet) {
         LOGE("Could not send video packet: %d", ret);
         return false;
     }
-    ret = avcodec_receive_frame(decoder->codec_ctx,
+    ret = avcodec_receive_frame(decoder->codec_ctx, decoder->frame);
-                                decoder->video_buffer->producer_frame);
     if (!ret) {
         // a frame was received
-        video_buffer_producer_offer_frame(decoder->video_buffer);
+        video_buffer_producer_offer_frame(decoder->video_buffer,
+                                          &decoder->frame);
     } else if (ret != AVERROR(EAGAIN)) {
         LOGE("Could not receive video frame: %d", ret);
         return false;
@@ -61,7 +70,7 @@ decoder_push(struct decoder *decoder, const AVPacket *packet) {
 #else
     int got_picture;
     int len = avcodec_decode_video2(decoder->codec_ctx,
-                                    decoder->video_buffer->decoding_frame,
+                                    decoder->frame,
                                     &got_picture,
                                     packet);
     if (len < 0) {

app/src/decoder.h

@@ -12,6 +12,7 @@ struct decoder {
     struct video_buffer *video_buffer;
 
     AVCodecContext *codec_ctx;
+    AVFrame *frame;
 };
 
 void

app/src/screen.c

@@ -356,6 +356,15 @@ screen_init(struct screen *screen, struct video_buffer *vb,
         return false;
     }
 
+    screen->frame = av_frame_alloc();
+    if (!screen->frame) {
+        LOGC("Could not create screen frame");
+        SDL_DestroyTexture(screen->texture);
+        SDL_DestroyRenderer(screen->renderer);
+        SDL_DestroyWindow(screen->window);
+        return false;
+    }
+
     // Reset the window size to trigger a SIZE_CHANGED event, to workaround
     // HiDPI issues with some SDL renderers when several displays having
     // different HiDPI scaling are connected
@@ -373,6 +382,7 @@ screen_show_window(struct screen *screen) {
 
 void
 screen_destroy(struct screen *screen) {
+    av_frame_free(&screen->frame);
     SDL_DestroyTexture(screen->texture);
     SDL_DestroyRenderer(screen->renderer);
     SDL_DestroyWindow(screen->window);
@@ -480,7 +490,8 @@ update_texture(struct screen *screen, const AVFrame *frame) {
 
 static bool
 screen_update_frame(struct screen *screen) {
-    const AVFrame *frame = video_buffer_consumer_take_frame(screen->vb);
+    video_buffer_consumer_take_frame(screen->vb, &screen->frame);
+    AVFrame *frame = screen->frame;
 
     fps_counter_add_rendered_frame(screen->fps_counter);
 

app/src/screen.h

@@ -36,6 +36,8 @@ struct screen {
     bool fullscreen;
     bool maximized;
     bool mipmaps;
+
+    AVFrame *frame;
 };
 
 struct screen_params {

app/src/video_buffer.c

@@ -8,24 +8,14 @@
 
 bool
 video_buffer_init(struct video_buffer *vb, bool wait_consumer) {
-    vb->producer_frame = av_frame_alloc();
-    if (!vb->producer_frame) {
-        goto error_0;
-    }
-
     vb->pending_frame = av_frame_alloc();
     if (!vb->pending_frame) {
-        goto error_1;
+        goto error_0;
-    }
-
-    vb->consumer_frame = av_frame_alloc();
-    if (!vb->consumer_frame) {
-        goto error_2;
     }
 
     bool ok = sc_mutex_init(&vb->mutex);
     if (!ok) {
-        goto error_3;
+        goto error_1;
     }
 
     vb->wait_consumer = wait_consumer;
@@ -33,7 +23,7 @@ video_buffer_init(struct video_buffer *vb, bool wait_consumer) {
         ok = sc_cond_init(&vb->pending_frame_consumed_cond);
         if (!ok) {
             sc_mutex_destroy(&vb->mutex);
-            goto error_2;
+            goto error_1;
         }
         // interrupted is not used if wait_consumer is disabled since offering
         // a frame will never block
@@ -49,12 +39,8 @@ video_buffer_init(struct video_buffer *vb, bool wait_consumer) {
 
     return true;
 
-error_3:
-    av_frame_free(&vb->consumer_frame);
-error_2:
-    av_frame_free(&vb->pending_frame);
 error_1:
-    av_frame_free(&vb->producer_frame);
+    av_frame_free(&vb->pending_frame);
 error_0:
     return false;
 }
@@ -65,9 +51,7 @@ video_buffer_destroy(struct video_buffer *vb) {
         sc_cond_destroy(&vb->pending_frame_consumed_cond);
     }
     sc_mutex_destroy(&vb->mutex);
-    av_frame_free(&vb->consumer_frame);
     av_frame_free(&vb->pending_frame);
-    av_frame_free(&vb->producer_frame);
 }
 
 static inline void
@@ -89,7 +73,7 @@ video_buffer_set_consumer_callbacks(struct video_buffer *vb,
 }
 
 void
-video_buffer_producer_offer_frame(struct video_buffer *vb) {
+video_buffer_producer_offer_frame(struct video_buffer *vb, AVFrame **pframe) {
     assert(vb->cbs);
 
     sc_mutex_lock(&vb->mutex);
@@ -101,7 +85,7 @@ video_buffer_producer_offer_frame(struct video_buffer *vb) {
     }
 
     av_frame_unref(vb->pending_frame);
-    swap_frames(&vb->producer_frame, &vb->pending_frame);
+    swap_frames(pframe, &vb->pending_frame);
 
     bool skipped = !vb->pending_frame_consumed;
     vb->pending_frame_consumed = false;
@@ -116,13 +100,13 @@ video_buffer_producer_offer_frame(struct video_buffer *vb) {
     }
 }
 
-const AVFrame *
+void
-video_buffer_consumer_take_frame(struct video_buffer *vb) {
+video_buffer_consumer_take_frame(struct video_buffer *vb, AVFrame **pframe) {
     sc_mutex_lock(&vb->mutex);
     assert(!vb->pending_frame_consumed);
     vb->pending_frame_consumed = true;
 
-    swap_frames(&vb->consumer_frame, &vb->pending_frame);
+    swap_frames(pframe, &vb->pending_frame);
     av_frame_unref(vb->pending_frame);
 
     if (vb->wait_consumer) {
@@ -130,9 +114,6 @@ video_buffer_consumer_take_frame(struct video_buffer *vb) {
         sc_cond_signal(&vb->pending_frame_consumed_cond);
     }
     sc_mutex_unlock(&vb->mutex);
-
-    // consumer_frame is only written from this thread, no need to lock
-    return vb->consumer_frame;
 }
 
 void

app/src/video_buffer.h

@@ -29,9 +29,7 @@ typedef struct AVFrame AVFrame;
  */
 
 struct video_buffer {
-    AVFrame *producer_frame;
     AVFrame *pending_frame;
-    AVFrame *consumer_frame;
 
     sc_mutex mutex;
     bool wait_consumer; // never overwrite a pending frame if it is not consumed
@@ -67,13 +65,14 @@ video_buffer_set_consumer_callbacks(struct video_buffer *vb,
                                     void *cbs_userdata);
 
 // set the producer frame as ready for consuming
+// the produced frame is exchanged with an unused allocated frame
 void
-video_buffer_producer_offer_frame(struct video_buffer *vb);
+video_buffer_producer_offer_frame(struct video_buffer *vb, AVFrame **pframe);
 
-// mark the consumer frame as consumed and return it
+// mark the consumer frame as consumed and exchange it with an unused allocated
-// the frame is valid until the next call to this function
+// frame
-const AVFrame *
+void
-video_buffer_consumer_take_frame(struct video_buffer *vb);
+video_buffer_consumer_take_frame(struct video_buffer *vb, AVFrame **pframe);
 
 // wake up and avoid any blocking call
 void