Add packet sink trait

This trait will allow to abstract the concrete sink types from the
packet producer (stream.c).

app/src/trait/packet_sink.h

@@ -0,0 +1,27 @@
+#ifndef SC_PACKET_SINK
+#define SC_PACKET_SINK
+
+#include "common.h"
+
+#include <assert.h>
+#include <stdbool.h>
+
+typedef struct AVCodec AVCodec;
+typedef struct AVPacket AVPacket;
+
+/**
+ * Packet sink trait.
+ *
+ * Component able to receive AVPackets should implement this trait.
+ */
+struct sc_packet_sink {
+    const struct sc_packet_sink_ops *ops;
+};
+
+struct sc_packet_sink_ops {
+    bool (*open)(struct sc_packet_sink *sink, const AVCodec *codec);
+    void (*close)(struct sc_packet_sink *sink);
+    bool (*push)(struct sc_packet_sink *sink, const AVPacket *packet);
+};
+
+#endif