gstreamer: Fallback to S/W decoder if H/W one is not working

In case the H/W decoder is not able to decode the stream (like too high
profile) try the S/W version.
This is done detecting the failure and trying to recreate the pipeline
in case:
- we are using a H/W pipeline;
- we didn't decode any frame (otherwise it means we lost the beginning
  or it was not a problem of H/W decoder).

Signed-off-by: Frediano Ziglio <freddy77@gmail.com>
Acked-by: Vivek Kasireddy <vivek.kasireddy@intel.com>

src/channel-display-gst.c

@@ -48,6 +48,8 @@ typedef struct SpiceGstDecoder {
     GstElement *pipeline;
     GstClock *clock;
     GstBus *bus;
+    bool is_hw_pipeline;
+    bool frame_removed;
 
     /* ---------- Decoding and display queues ---------- */
 
@@ -125,6 +127,7 @@ static void free_gst_frame(SpiceGstFrame *gstframe)
 /* ---------- GStreamer pipeline ---------- */
 
 static void schedule_frame(SpiceGstDecoder *decoder);
+static void try_sw_pipeline(SpiceGstDecoder *decoder);
 
 RECORDER(frames_stats, 64, "Frames statistics");
 
@@ -231,6 +234,7 @@ static guint32 pop_up_to_frame(SpiceGstDecoder *decoder, const SpiceGstFrame *po
     SpiceGstFrame *gstframe;
     guint32 freed = 0;
 
+    decoder->frame_removed = true;
     while ((gstframe = g_queue_pop_head(decoder->decoding_queue)) != popframe) {
         free_gst_frame(gstframe);
         freed++;
@@ -371,6 +375,7 @@ static void free_pipeline(SpiceGstDecoder *decoder)
     decoder->clock = NULL;
     gst_object_unref(decoder->pipeline);
     decoder->pipeline = NULL;
+    decoder->is_hw_pipeline = false;
 }
 
 static gboolean handle_pipeline_message(GstBus *bus, GstMessage *msg, gpointer video_decoder)
@@ -390,8 +395,11 @@ static gboolean handle_pipeline_message(GstBus *bus, GstMessage *msg, gpointer v
         }
         g_clear_error(&err);
 
-        /* We won't be able to process any more frame anyway */
+        bool was_hw = decoder->is_hw_pipeline;
         free_pipeline(decoder);
+        if (was_hw && !decoder->frame_removed) {
+            try_sw_pipeline(decoder);
+        }
         break;
     }
     case GST_MESSAGE_STREAM_START: {
@@ -672,6 +680,7 @@ static bool try_intel_hw_pipeline(SpiceGstDecoder *decoder)
     }
 
     decoder->pipeline = pipeline;
+    decoder->is_hw_pipeline = true;
     return launch_pipeline(decoder);
 
 err:
@@ -704,7 +713,7 @@ err:
     return false;
 }
 
-static gboolean create_pipeline(SpiceGstDecoder *decoder)
+static gboolean create_pipeline(SpiceGstDecoder *decoder, bool try_hw_pipeline)
 {
     GstElement *playbin, *sink;
     SpiceGstPlayFlags flags;
@@ -714,7 +723,7 @@ static gboolean create_pipeline(SpiceGstDecoder *decoder)
 
     if (vendor == VENDOR_GPU_DETECTED ||
         vendor == VENDOR_GPU_UNKNOWN) {
-        if (try_intel_hw_pipeline(decoder)) {
+        if (try_hw_pipeline && try_intel_hw_pipeline(decoder)) {
             return TRUE;
         }
     }
@@ -997,7 +1006,7 @@ VideoDecoder* create_gstreamer_decoder(int codec_type, display_stream *stream)
         g_mutex_init(&decoder->queues_mutex);
         decoder->decoding_queue = g_queue_new();
 
-        if (!create_pipeline(decoder)) {
+        if (!create_pipeline(decoder, true)) {
             decoder->base.destroy((VideoDecoder*)decoder);
             decoder = NULL;
         }
@@ -1066,3 +1075,25 @@ gboolean gstvideo_has_codec(int codec_type)
     gst_plugin_feature_list_free(all_decoders);
     return TRUE;
 }
+
+static void try_sw_pipeline(SpiceGstDecoder *decoder)
+{
+    // try to create a S/W pipeline
+    if (!create_pipeline(decoder, false)) {
+        return;
+    }
+
+    // replay the old queue
+    g_mutex_lock(&decoder->queues_mutex);
+    GList *l = g_queue_peek_head_link(decoder->decoding_queue);
+    while (l) {
+        const SpiceGstFrame *gstframe = l->data;
+        GstBuffer *buf = gst_buffer_ref(gstframe->encoded_buffer);
+        if (gst_app_src_push_buffer(decoder->appsrc, buf) != GST_FLOW_OK) {
+            SPICE_DEBUG("GStreamer error: unable to push frame");
+            stream_dropped_frame_on_playback(decoder->base.stream);
+        }
+        l = l->next;
+    }
+    g_mutex_unlock(&decoder->queues_mutex);
+}