Take into account changes made in 8835e757922c, 8c2101254051 and
possibly other other commits.
Add MAX_DECODED_FRAMES to define how many decoded frames GStreamer
should queue.
Signed-off-by: Francois Gouget <fgouget@xxxxxxxxxxxxxxx>
---
src/channel-display-gst.c | 63 +++++++++++++++++++++++----------------
1 file changed, 38 insertions(+), 25 deletions(-)
diff --git a/src/channel-display-gst.c b/src/channel-display-gst.c
index 50f29060..b5b8d51a 100644
--- a/src/channel-display-gst.c
+++ b/src/channel-display-gst.c
@@ -62,6 +62,9 @@ typedef struct SpiceGstDecoder {
#define VALID_VIDEO_CODEC_TYPE(codec) \
(codec > 0 && codec < G_N_ELEMENTS(gst_opts))
+/* Decoded frames are big so limit how many are queued by GStreamer */
+#define MAX_DECODED_FRAMES 2
+
/* GstPlayFlags enum is in plugin's header which should not be exported.
* https://bugzilla.gnome.org/show_bug.cgi?id=784279
*/
@@ -320,11 +323,14 @@ static void schedule_frame(SpiceGstDecoder *decoder)
/* GStreamer thread
*
- * We cannot use GStreamer's signals because they are not always run in
- * the main context. So use a callback (lower overhead) and have it pull
- * the sample to avoid a race with free_pipeline(). This means queuing the
- * decoded frames outside GStreamer. So while we're at it, also schedule
- * the frame display ourselves in schedule_frame().
+ * Decoded frames are big so we rely on GStreamer to limit how many are
+ * buffered (see MAX_DECODED_FRAMES). This means we must not pull the samples
+ * as soon as they become available. Instead just increment pending_samples so
+ * schedule_frame() knows whether it can pull a new sample when it needs one.
+ *
+ * Note that GStreamer's signals are not always run in the main context, hence
+ * the schedule_frame() + display_frame() mechanism. So we might as well use
+ * a callback here (lower overhead).
*/
static GstFlowReturn new_sample(GstAppSink *gstappsink, gpointer video_decoder)
{
@@ -535,7 +541,7 @@ static gboolean create_pipeline(SpiceGstDecoder *decoder)
GstAppSinkCallbacks appsink_cbs = { NULL };
appsink_cbs.new_sample = new_sample;
gst_app_sink_set_callbacks(decoder->appsink, &appsink_cbs, decoder, NULL);
- gst_app_sink_set_max_buffers(decoder->appsink, 2);
+ gst_app_sink_set_max_buffers(decoder->appsink, MAX_DECODED_FRAMES);
gst_app_sink_set_drop(decoder->appsink, FALSE);
}
bus = gst_pipeline_get_bus(GST_PIPELINE(decoder->pipeline));
@@ -612,37 +618,44 @@ static void spice_gst_decoder_destroy(VideoDecoder *video_decoder)
*
* 1) frame->data, which contains the compressed frame data, is wrapped in a GstBuffer
* (encoded_buffer) which owns the SpiceFrame.
- * 2) A SpiceGstFrame is created to keep track of SpiceFrame (encoded_frame), and some
- * additional metadata. The encoded_buffer is referenced and the SpiceGstFrame is then
- * pushed into the decoding_queue.
+ * 2) A SpiceGstFrame is created to keep track of SpiceFrame (encoded_frame),
+ * and additional metadata among which GStreamer's encoded_buffer the
+ * refcount of which is incremented. The SpiceGstFrame is then pushed into
+ * the decoding_queue.
*
* If GstVideoOverlay is used (window handle was obtained successfully at the widget):
* 3) Decompressed frames will be rendered to widget directly from GStreamer's pipeline
* using some GStreamer sink plugin which implements the GstVideoOverlay interface
* (last step).
* 4) As soon as GStreamer's pipeline no longer needs the compressed frame it will
- * unref the encoded_buffer
- * 5) Once a decoded buffer arrives to the sink (notified by probe event) we will pop
+ * unref the encoded_buffer.
+ * 5) Once a decoded buffer arrives to the sink sink_event_probe() will pop
* its matching SpiceGstFrame from the decoding_queue and free it using
- * free_gst_frame, this will also unref the encoded_buffer which will allow
- * GStreamer to call spice_frame_free and free its encoded_frame.
+ * free_gst_frame(). This will also unref the encoded_buffer which will
+ * allow GStreamer to call spice_frame_free() and free its encoded_frame.
*
* Otherwise appsink is used:
* 3) Once the decompressed frame is available the GStreamer pipeline calls
* new_sample() in the GStreamer thread.
- * 4) new_sample() then matches the decompressed frame to a SpiceGstFrame from
- * the decoding queue using the GStreamer timestamp information to deal with
- * dropped frames. The SpiceGstFrame is popped from the decoding_queue.
- * 5) new_sample() then attaches the decompressed frame to the SpiceGstFrame,
- * set into display_frame and calls schedule_frame().
- * 6) schedule_frame() then uses gstframe->encoded_frame->mm_time to arrange for
- * display_frame() to be called, in the main thread, at the right time for
- * the next frame.
- * 7) display_frame() uses SpiceGstFrame from display_frame and calls
+ * 4) new_sample() then increments the pending_samples count and calls
+ * schedule_frame().
+ * 5) schedule_frame() is called whenever a new frame might need to be
+ * displayed. If that is the case and pending_samples is non-zero it calls
+ * fetch_pending_sample().
+ * 6) fetch_pending_sample() grabs GStreamer's latest sample and then calls
+ * get_decoded_frame() which compares the GStreamer's buffer timestamp to
+ * gstframe->encoded_frame->mm_time to match it with a decoding_queue
+ * entry.
+ * 7) fetch_pending_sample() then attaches the sample to the SpiceGstFrame,
+ * and sets display_frame.
+ * 8) schedule_frame() then uses display_frame->encoded_frame->mm_time to
+ * arrange for display_frame() to be called, in the main thread, at the
+ * right time.
+ * 9) display_frame() uses SpiceGstFrame from display_frame and calls
* stream_display_frame().
- * 8) display_frame() then calls to free_gst_frame to free the SpiceGstFrame and
- * unref the encoded_buffer which allows GStreamer to call spice_frame_free
- * and free its encoded_frame.
+ * 10) display_frame() then calls free_gst_frame() to free the SpiceGstFrame
+ * and unref the encoded_buffer which allows GStreamer to call
+ * spice_frame_free() and free its encoded_frame.
*/
static gboolean spice_gst_decoder_queue_frame(VideoDecoder *video_decoder,
SpiceFrame *frame, int latency)
--
2.20.1
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