accel: clarify usage of extractData callback

Moves the frame reference switch to the extractData wrapper function
to clarify that the output frame received in the callback is indeed
an output and not a temporary frame.

Change-Id: Ic21a3a7517647d263621b23debe1a4fb7f810a8e
Reviewed-by: Guillaume Roguez <guillaume.roguez@savoirfairelinux.com>

src/media/video/accel.cpp

@@ -124,8 +124,12 @@ HardwareAccel::extractData(VideoFrame& input)
         auto outFrame = output->pointer();
         outFrame->format = AV_PIX_FMT_YUV420P;
 
-        // call the acceleration's implementation
         extractData(input, *output);
+
+        // move outFrame into inFrame so the caller receives extracted image data
+        // but we have to delete inFrame first
+        av_frame_unref(inFrame);
+        av_frame_move_ref(inFrame, outFrame);
     } catch (const std::runtime_error& e) {
         fail(false);
         RING_ERR("%s", e.what());

src/media/video/accel.h

@@ -53,8 +53,6 @@ class HardwareAccel {
         virtual bool check() = 0;
         virtual bool init() = 0;
         virtual int allocateBuffer(AVFrame* frame, int flags) = 0;
-        // The reference to the extracted frame should be moved to input
-        // as that's the frame returned to the MediaDecoder
         virtual void extractData(VideoFrame& input, VideoFrame& output) = 0;
 
     protected:

src/media/video/v4l2/vaapi.cpp

@@ -71,9 +71,6 @@ VaapiAccel::extractData(VideoFrame& input, VideoFrame& output)
     if (av_frame_copy_props(outFrame, inFrame) < 0 ) {
         av_frame_unref(outFrame);
     }
-
-    av_frame_unref(inFrame);
-    av_frame_move_ref(inFrame, outFrame);
 }
 
 bool