Make video buffer more generic

Video buffer is a tool between a frame producer and a frame consumer.

For now, it is used between a decoder and a renderer, but in the future
another instance might be used to swscale decoded frames.

app/src/decoder.c

@@ -15,8 +15,8 @@
 static void
 push_frame(struct decoder *decoder) {
     bool previous_frame_skipped;
-    video_buffer_offer_decoded_frame(decoder->video_buffer,
-                                     &previous_frame_skipped);
+    video_buffer_producer_offer_frame(decoder->video_buffer,
+                                      &previous_frame_skipped);
     if (previous_frame_skipped) {
         fps_counter_add_skipped_frame(decoder->fps_counter);
         // the previous EVENT_NEW_FRAME will consume this frame
@@ -69,7 +69,7 @@ decoder_push(struct decoder *decoder, const AVPacket *packet) {
         return false;
     }
     ret = avcodec_receive_frame(decoder->codec_ctx,
-                                decoder->video_buffer->decoding_frame);
+                                decoder->video_buffer->producer_frame);
     if (!ret) {
         // a frame was received
         push_frame(decoder);

app/src/screen.c

@@ -453,7 +453,7 @@ update_texture(struct screen *screen, const AVFrame *frame) {
 
 static bool
 screen_update_frame(struct screen *screen) {
-    const AVFrame *frame = video_buffer_take_rendering_frame(screen->vb);
+    const AVFrame *frame = video_buffer_consumer_take_frame(screen->vb);
 
     fps_counter_add_rendered_frame(screen->fps_counter);
 

app/src/video_buffer.c

@@ -7,9 +7,9 @@
 #include "util/log.h"
 
 bool
-video_buffer_init(struct video_buffer *vb, bool render_expired_frames) {
-    vb->decoding_frame = av_frame_alloc();
-    if (!vb->decoding_frame) {
+video_buffer_init(struct video_buffer *vb, bool wait_consumer) {
+    vb->producer_frame = av_frame_alloc();
+    if (!vb->producer_frame) {
         goto error_0;
     }
 
@@ -18,8 +18,8 @@ video_buffer_init(struct video_buffer *vb, bool render_expired_frames) {
         goto error_1;
     }
 
-    vb->rendering_frame = av_frame_alloc();
-    if (!vb->rendering_frame) {
+    vb->consumer_frame = av_frame_alloc();
+    if (!vb->consumer_frame) {
         goto error_2;
     }
 
@@ -28,73 +28,72 @@ video_buffer_init(struct video_buffer *vb, bool render_expired_frames) {
         goto error_3;
     }
 
-    vb->render_expired_frames = render_expired_frames;
-    if (render_expired_frames) {
+    vb->wait_consumer = wait_consumer;
+    if (wait_consumer) {
         ok = sc_cond_init(&vb->pending_frame_consumed_cond);
         if (!ok) {
             sc_mutex_destroy(&vb->mutex);
             goto error_2;
         }
-        // interrupted is not used if expired frames are not rendered
-        // since offering a frame will never block
+        // interrupted is not used if wait_consumer is disabled since offering
+        // a frame will never block
         vb->interrupted = false;
     }
 
-    // there is initially no rendering frame, so consider it has already been
-    // consumed
+    // there is initially no frame, so consider it has already been consumed
     vb->pending_frame_consumed = true;
 
     return true;
 
 error_3:
-    av_frame_free(&vb->rendering_frame);
+    av_frame_free(&vb->consumer_frame);
 error_2:
     av_frame_free(&vb->pending_frame);
 error_1:
-    av_frame_free(&vb->decoding_frame);
+    av_frame_free(&vb->producer_frame);
 error_0:
     return false;
 }
 
 void
 video_buffer_destroy(struct video_buffer *vb) {
-    if (vb->render_expired_frames) {
+    if (vb->wait_consumer) {
         sc_cond_destroy(&vb->pending_frame_consumed_cond);
     }
     sc_mutex_destroy(&vb->mutex);
-    av_frame_free(&vb->rendering_frame);
+    av_frame_free(&vb->consumer_frame);
     av_frame_free(&vb->pending_frame);
-    av_frame_free(&vb->decoding_frame);
+    av_frame_free(&vb->producer_frame);
 }
 
 static void
-video_buffer_swap_decoding_frame(struct video_buffer *vb) {
+video_buffer_swap_producer_frame(struct video_buffer *vb) {
     sc_mutex_assert(&vb->mutex);
-    AVFrame *tmp = vb->decoding_frame;
-    vb->decoding_frame = vb->pending_frame;
+    AVFrame *tmp = vb->producer_frame;
+    vb->producer_frame = vb->pending_frame;
     vb->pending_frame = tmp;
 }
 
 static void
-video_buffer_swap_rendering_frame(struct video_buffer *vb) {
+video_buffer_swap_consumer_frame(struct video_buffer *vb) {
     sc_mutex_assert(&vb->mutex);
-    AVFrame *tmp = vb->rendering_frame;
-    vb->rendering_frame = vb->pending_frame;
+    AVFrame *tmp = vb->consumer_frame;
+    vb->consumer_frame = vb->pending_frame;
     vb->pending_frame = tmp;
 }
 
 void
-video_buffer_offer_decoded_frame(struct video_buffer *vb,
-                                 bool *previous_frame_skipped) {
+video_buffer_producer_offer_frame(struct video_buffer *vb,
+                                  bool *previous_frame_skipped) {
     sc_mutex_lock(&vb->mutex);
-    if (vb->render_expired_frames) {
+    if (vb->wait_consumer) {
         // wait for the current (expired) frame to be consumed
         while (!vb->pending_frame_consumed && !vb->interrupted) {
             sc_cond_wait(&vb->pending_frame_consumed_cond, &vb->mutex);
         }
     }
 
-    video_buffer_swap_decoding_frame(vb);
+    video_buffer_swap_producer_frame(vb);
 
     *previous_frame_skipped = !vb->pending_frame_consumed;
     vb->pending_frame_consumed = false;
@@ -103,26 +102,26 @@ video_buffer_offer_decoded_frame(struct video_buffer *vb,
 }
 
 const AVFrame *
-video_buffer_take_rendering_frame(struct video_buffer *vb) {
+video_buffer_consumer_take_frame(struct video_buffer *vb) {
     sc_mutex_lock(&vb->mutex);
     assert(!vb->pending_frame_consumed);
     vb->pending_frame_consumed = true;
 
-    video_buffer_swap_rendering_frame(vb);
+    video_buffer_swap_consumer_frame(vb);
 
-    if (vb->render_expired_frames) {
+    if (vb->wait_consumer) {
         // unblock video_buffer_offer_decoded_frame()
         sc_cond_signal(&vb->pending_frame_consumed_cond);
     }
     sc_mutex_unlock(&vb->mutex);
 
-    // rendering_frame is only written from this thread, no need to lock
-    return vb->rendering_frame;
+    // consumer_frame is only written from this thread, no need to lock
+    return vb->consumer_frame;
 }
 
 void
 video_buffer_interrupt(struct video_buffer *vb) {
-    if (vb->render_expired_frames) {
+    if (vb->wait_consumer) {
         sc_mutex_lock(&vb->mutex);
         vb->interrupted = true;
         sc_mutex_unlock(&vb->mutex);

app/src/video_buffer.h

@@ -13,28 +13,28 @@ typedef struct AVFrame AVFrame;
 
 /**
  * There are 3 frames in memory:
- *  - one frame is held by the decoder (decoding_frame)
- *  - one frame is held by the renderer (rendering_frame)
- *  - one frame is shared between the decoder and the renderer (pending_frame)
+ *  - one frame is held by the producer (producer_frame)
+ *  - one frame is held by the consumer (consumer_frame)
+ *  - one frame is shared between the producer and the consumer (pending_frame)
  *
- * The decoder decodes a packet into the decoding_frame (it may takes time).
+ * The producer generates a frame into the producer_frame (it may takes time).
  *
- * Once the frame is decoded, it calls video_buffer_offer_decoded_frame(),
- * which swaps the decoding and pending frames.
+ * Once the frame is produced, it calls video_buffer_producer_offer_frame(),
+ * which swaps the producer and pending frames.
  *
- * When the renderer is notified that a new frame is available, it calls
- * video_buffer_take_rendering_frame() to retrieve it, which swaps the pending
- * and rendering frames. The frame is valid until the next call, without
- * blocking the decoder.
+ * When the consumer is notified that a new frame is available, it calls
+ * video_buffer_consumer_take_frame() to retrieve it, which swaps the pending
+ * and consumer frames. The frame is valid until the next call, without
+ * blocking the producer.
  */
 
 struct video_buffer {
-    AVFrame *decoding_frame;
+    AVFrame *producer_frame;
     AVFrame *pending_frame;
-    AVFrame *rendering_frame;
+    AVFrame *consumer_frame;
 
     sc_mutex mutex;
-    bool render_expired_frames;
+    bool wait_consumer; // never overwrite a pending frame if it is not consumed
     bool interrupted;
 
     sc_cond pending_frame_consumed_cond;
@@ -42,21 +42,21 @@ struct video_buffer {
 };
 
 bool
-video_buffer_init(struct video_buffer *vb, bool render_expired_frames);
+video_buffer_init(struct video_buffer *vb, bool wait_consumer);
 
 void
 video_buffer_destroy(struct video_buffer *vb);
 
-// set the decoded frame as ready for rendering
+// set the producer frame as ready for consuming
 // the output flag is set to report whether the previous frame has been skipped
 void
-video_buffer_offer_decoded_frame(struct video_buffer *vb,
-                                 bool *previous_frame_skipped);
+video_buffer_producer_offer_frame(struct video_buffer *vb,
+                                  bool *previous_frame_skipped);
 
-// mark the rendering frame as consumed and return it
+// mark the consumer frame as consumed and return it
 // the frame is valid until the next call to this function
 const AVFrame *
-video_buffer_take_rendering_frame(struct video_buffer *vb);
+video_buffer_consumer_take_frame(struct video_buffer *vb);
 
 // wake up and avoid any blocking call
 void