Extract packet merging

Config packets must be prepended to the next media packet. Extract the
logic to a new sc_packet_merger helper to simplify the demuxer code.

app/meson.build

@@ -21,6 +21,7 @@ src = [
     'src/mouse_inject.c',
     'src/opengl.c',
     'src/options.c',
+    'src/packet_merger.c',
     'src/receiver.c',
     'src/recorder.c',
     'src/scrcpy.c',

app/src/demuxer.c

@@ -6,6 +6,7 @@
 
 #include "decoder.h"
 #include "events.h"
+#include "packet_merger.h"
 #include "recorder.h"
 #include "util/binary.h"
 #include "util/log.h"
@@ -120,48 +121,7 @@ push_packet_to_sinks(struct sc_demuxer *demuxer, const AVPacket *packet) {
 
 static bool
 sc_demuxer_push_packet(struct sc_demuxer *demuxer, AVPacket *packet) {
-    bool is_config = packet->pts == AV_NOPTS_VALUE;
-
-    // A config packet must not be decoded immediately (it contains no
-    // frame); instead, it must be concatenated with the future data packet.
-    if (demuxer->pending || is_config) {
-        if (demuxer->pending) {
-            size_t offset = demuxer->pending->size;
-            if (av_grow_packet(demuxer->pending, packet->size)) {
-                LOG_OOM();
-                return false;
-            }
-
-            memcpy(demuxer->pending->data + offset, packet->data, packet->size);
-        } else {
-            demuxer->pending = av_packet_alloc();
-            if (!demuxer->pending) {
-                LOG_OOM();
-                return false;
-            }
-            if (av_packet_ref(demuxer->pending, packet)) {
-                LOG_OOM();
-                av_packet_free(&demuxer->pending);
-                return false;
-            }
-        }
-
-        if (!is_config) {
-            // prepare the concat packet to send to the decoder
-            demuxer->pending->pts = packet->pts;
-            demuxer->pending->dts = packet->dts;
-            demuxer->pending->flags = packet->flags;
-            packet = demuxer->pending;
-        }
-    }
-
     bool ok = push_packet_to_sinks(demuxer, packet);
-
-    if (!is_config && demuxer->pending) {
-        // the pending packet must be discarded (consumed or error)
-        av_packet_free(&demuxer->pending);
-    }
-
     if (!ok) {
         LOGE("Could not process packet");
         return false;
@@ -228,6 +188,9 @@ run_demuxer(void *data) {
         goto end;
     }
 
+    struct sc_packet_merger merger;
+    sc_packet_merger_init(&merger);
+
     AVPacket *packet = av_packet_alloc();
     if (!packet) {
         LOG_OOM();
@@ -242,6 +205,13 @@ run_demuxer(void *data) {
             break;
         }
 
+        // Prepend any config packet to the next media packet
+        ok = sc_packet_merger_merge(&merger, packet);
+        if (!ok) {
+            av_packet_unref(packet);
+            break;
+        }
+
         ok = sc_demuxer_push_packet(demuxer, packet);
         av_packet_unref(packet);
         if (!ok) {
@@ -252,9 +222,7 @@ run_demuxer(void *data) {
 
     LOGD("End of frames");
 
-    if (demuxer->pending) {
-        av_packet_free(&demuxer->pending);
-    }
+    sc_packet_merger_destroy(&merger);
 
     av_packet_free(&packet);
 finally_close_sinks:
@@ -269,7 +237,6 @@ void
 sc_demuxer_init(struct sc_demuxer *demuxer, sc_socket socket,
                 const struct sc_demuxer_callbacks *cbs, void *cbs_userdata) {
     demuxer->socket = socket;
-    demuxer->pending = NULL;
     demuxer->sink_count = 0;
 
     assert(cbs && cbs->on_ended);

app/src/demuxer.h

@@ -21,10 +21,6 @@ struct sc_demuxer {
     struct sc_packet_sink *sinks[SC_DEMUXER_MAX_SINKS];
     unsigned sink_count;
 
-    // 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;
 };

app/src/packet_merger.c

@@ -0,0 +1,48 @@
+#include "packet_merger.h"
+
+#include "util/log.h"
+
+void
+sc_packet_merger_init(struct sc_packet_merger *merger) {
+    merger->config = NULL;
+}
+
+void
+sc_packet_merger_destroy(struct sc_packet_merger *merger) {
+    free(merger->config);
+}
+
+bool
+sc_packet_merger_merge(struct sc_packet_merger *merger, AVPacket *packet) {
+    bool is_config = packet->pts == AV_NOPTS_VALUE;
+
+    if (is_config) {
+        free(merger->config);
+
+        merger->config = malloc(packet->size);
+        if (!merger->config) {
+            LOG_OOM();
+            return false;
+        }
+
+        memcpy(merger->config, packet->data, packet->size);
+        merger->config_size = packet->size;
+    } else if (merger->config) {
+        size_t config_size = merger->config_size;
+        size_t media_size = packet->size;
+
+        if (av_grow_packet(packet, config_size)) {
+            LOG_OOM();
+            return false;
+        }
+
+        memmove(packet->data + config_size, packet->data, media_size);
+        memcpy(packet->data, merger->config, config_size);
+
+        free(merger->config);
+        merger->config = NULL;
+        // merger->size is meaningless when merger->config is NULL
+    }
+
+    return true;
+}

app/src/packet_merger.h

@@ -0,0 +1,43 @@
+#ifndef SC_PACKET_MERGER_H
+#define SC_PACKET_MERGER_H
+
+#include "common.h"
+
+#include <stdbool.h>
+#include <stdint.h>
+#include <libavcodec/avcodec.h>
+
+/**
+ * Config packets (containing the SPS/PPS) are sent in-band. A new config
+ * packet is sent whenever a new encoding session is started (on start and on
+ * device orientation change).
+ *
+ * Every time a config packet is received, it must be sent alone (for recorder
+ * extradata), then concatenated to the next media packet (for correct decoding
+ * and recording).
+ *
+ * This helper reads every input packet and modifies each media packet which
+ * immediately follows a config packet to prepend the config packet payload.
+ */
+
+struct sc_packet_merger {
+    uint8_t *config;
+    size_t config_size;
+};
+
+void
+sc_packet_merger_init(struct sc_packet_merger *merger);
+
+void
+sc_packet_merger_destroy(struct sc_packet_merger *merger);
+
+/**
+ * If the packet is a config packet, then keep its data for later.
+ * Otherwise (if the packet is a media packet), then if a config packet is
+ * pending, prepend the config packet to this packet (so the packet is
+ * modified!).
+ */
+bool
+sc_packet_merger_merge(struct sc_packet_merger *merger, AVPacket *packet);
+
+#endif