From 3e70f00209520b3395a80fb2b69b2914885b6894 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Sebastian=20Dr=C3=B6ge?= <sebastian@centricular.com>
Date: Mon, 27 Nov 2017 17:41:52 +0200
Subject: [PATCH] decklinkaudiosink: Check also against the clock if we run
 ahead of the clock too much

The buffer level as reported by the Decklink driver is completely
unreliable, and we could otherwise easily run ahead >1s if we're
unlucky.

https://bugzilla.gnome.org/show_bug.cgi?id=790114
---
 sys/decklink/gstdecklinkaudiosink.cpp | 37 ++++++++++++++++++++++++---
 1 file changed, 33 insertions(+), 4 deletions(-)

diff --git a/sys/decklink/gstdecklinkaudiosink.cpp b/sys/decklink/gstdecklinkaudiosink.cpp
index c97c074472..e39ee45449 100644
--- a/sys/decklink/gstdecklinkaudiosink.cpp
+++ b/sys/decklink/gstdecklinkaudiosink.cpp
@@ -585,6 +585,9 @@ gst_decklink_audio_sink_render (GstBaseSink * bsink, GstBuffer * buffer)
         self->info.rate);
     guint32 buffered_samples;
     GstClockTime buffered_time;
+    guint32 written = 0;
+    GstClock *clock;
+    GstClockTime clock_ahead;
 
     if (GST_BASE_SINK_CAST (self)->flushing) {
       flow_ret = GST_FLOW_FLUSHING;
@@ -619,6 +622,35 @@ gst_decklink_audio_sink_render (GstBaseSink * bsink, GstBuffer * buffer)
     else
       running_time = 0;
 
+    clock = gst_element_get_clock (GST_ELEMENT_CAST (self));
+    clock_ahead = 0;
+    if (clock) {
+      GstClockTime clock_now = gst_clock_get_time (clock);
+      GstClockTime base_time =
+          gst_element_get_base_time (GST_ELEMENT_CAST (self));
+      gst_object_unref (clock);
+      clock = NULL;
+
+      if (clock_now != GST_CLOCK_TIME_NONE && base_time != GST_CLOCK_TIME_NONE) {
+        GST_DEBUG_OBJECT (self,
+            "Clock time %" GST_TIME_FORMAT ", base time %" GST_TIME_FORMAT
+            ", target running time %" GST_TIME_FORMAT,
+            GST_TIME_ARGS (clock_now), GST_TIME_ARGS (base_time),
+            GST_TIME_ARGS (running_time));
+        if (clock_now > base_time)
+          clock_now -= base_time;
+        else
+          clock_now = 0;
+
+        if (clock_now < running_time)
+          clock_ahead = running_time - clock_now;
+      }
+    }
+
+    GST_DEBUG_OBJECT (self,
+        "Ahead %" GST_TIME_FORMAT " of the clock running time",
+        GST_TIME_ARGS (clock_ahead));
+
     if (self->output->
         output->GetBufferedAudioSampleFrameCount (&buffered_samples) != S_OK)
       buffered_samples = 0;
@@ -630,7 +662,7 @@ gst_decklink_audio_sink_render (GstBaseSink * bsink, GstBuffer * buffer)
         "Buffered %" GST_TIME_FORMAT " in the driver (%u samples)",
         GST_TIME_ARGS (buffered_time), buffered_samples);
     // We start waiting once we have more than buffer-time buffered
-    if (buffered_time > self->buffer_time) {
+    if (buffered_time > self->buffer_time || clock_ahead > self->buffer_time) {
       GstClockReturn clock_ret;
       GstClockTime wait_time = running_time;
 
@@ -666,7 +698,6 @@ gst_decklink_audio_sink_render (GstBaseSink * bsink, GstBuffer * buffer)
         &schedule_time, &schedule_time_duration);
 
     if (!self->output->started) {
-      guint32 written = 0;
       GST_LOG_OBJECT (self, "Writing audio frame synchronously because PAUSED");
 
       ret =
@@ -695,8 +726,6 @@ gst_decklink_audio_sink_render (GstBaseSink * bsink, GstBuffer * buffer)
       else
         written_all += written;
     } else {
-      guint32 written = 0;
-
       GST_LOG_OBJECT (self, "Scheduling audio samples at %" GST_TIME_FORMAT
           " with duration %" GST_TIME_FORMAT, GST_TIME_ARGS (schedule_time),
           GST_TIME_ARGS (schedule_time_duration));