hd-rum-decompress: handle nullptr ASAP

1. capture filter may return nullptr - handle it immediately
2. we may receive nullptr as input video_frame - return immediately
(as hd-rum decompress doesn't handle audio, either)

Author: MartinPulec

src/hd-rum-translator/hd-rum-decompress.cpp

@@ -103,21 +103,22 @@ void state_transcoder_decompress::frame_arrived(void *state, struct video_frame
 {
         PROFILE_FUNC;
         auto *s = (struct state_transcoder_decompress *) state;
+        if (f == nullptr) { // skip poison pill from vdisp/pipe
+                return;
+        }
         if (a) {
                 LOG(LOG_LEVEL_WARNING) << "Unexpectedly receiving audio!\n";
                 AUDIO_FRAME_DISPOSE(a);
         }
         auto deleter = vf_free;
         // apply capture filter
-        if (f) {
-                f = capture_filter(s->capture_filter_state, f);
+        f = capture_filter(s->capture_filter_state, f);
+        if (f == nullptr) {
+                return;
         }
-        if (f && f->callbacks.dispose) {
+        if (f->callbacks.dispose != nullptr) {
                 deleter = f->callbacks.dispose;
         }
-        if (!f) {
-                return;
-        }
 
         unique_lock<mutex> l(s->lock);
         if (s->received_frame.size() >= MAX_QUEUE_SIZE) {

src/video_display/pipe.h

@@ -41,11 +41,23 @@
 struct audio_frame;
 struct video_frame;
 
-typedef void pipe_frame_arrived_t(void *state, struct video_frame *,
-                                   struct audio_frame *);
+/**
+ * callback called when A/V frame was received
+ *
+ * @note
+ * Current implementation passes always `v != nullptr`, `a` can be nullptr or
+ * not depending if audio is received (audio frame attached always to
+ * video_frame). `v == nullptr` means a poison pill (last frame signalizing an
+ * end).
+ */
+typedef void pipe_frame_arrived_t(void *state, struct video_frame *v,
+                                  struct audio_frame *a);
 
+/**
+ * passed as a pointer to vcap/pipe
+ */
 struct pipe_frame_recv_delegate {
-        void *state;
+        void *state; //< pointer passed as first argument to frame_arrived
         /**
          * Implementing method must release both audio and video frame received
          * as parameters with AUDIO_FRAME_DISPOSE() and VIDEO_FRAME_DISPOSE().