Rename stream to sc_demuxer

For consistency with recorder and decoder, name the component which
demuxes a "demuxer".

And add the missing sc_ prefix.

app/src/demuxer.h

@@ -0,0 +1,51 @@
+#ifndef SC_DEMUXER_H
+#define SC_DEMUXER_H
+
+#include "common.h"
+
+#include <stdbool.h>
+#include <stdint.h>
+#include <libavcodec/avcodec.h>
+#include <libavformat/avformat.h>
+
+#include "trait/packet_sink.h"
+#include "util/net.h"
+#include "util/thread.h"
+
+#define SC_DEMUXER_MAX_SINKS 2
+
+struct sc_demuxer {
+    sc_socket socket;
+    sc_thread thread;
+
+    struct sc_packet_sink *sinks[SC_DEMUXER_MAX_SINKS];
+    unsigned sink_count;
+
+    AVCodecContext *codec_ctx;
+    AVCodecParserContext *parser;
+    // successive packets may need to be concatenated, until a non-config
+    // packet is available
+    AVPacket *pending;
+
+    const struct sc_demuxer_callbacks *cbs;
+    void *cbs_userdata;
+};
+
+struct sc_demuxer_callbacks {
+    void (*on_eos)(struct sc_demuxer *demuxer, void *userdata);
+};
+
+void
+sc_demuxer_init(struct sc_demuxer *demuxer, sc_socket socket,
+                const struct sc_demuxer_callbacks *cbs, void *cbs_userdata);
+
+void
+sc_demuxer_add_sink(struct sc_demuxer *demuxer, struct sc_packet_sink *sink);
+
+bool
+sc_demuxer_start(struct sc_demuxer *demuxer);
+
+void
+sc_demuxer_join(struct sc_demuxer *demuxer);
+
+#endif