From 588ac0ae6fdfb55c612cc84f5426cbf1ee4aec4e Mon Sep 17 00:00:00 2001
From: Havard Graff <havard.graff@tandberg.com>
Date: Tue, 8 Feb 2011 18:27:43 +0100
Subject: [PATCH] baseaudiosink: don't allow aligning behind the read-segment

Given a large enough drift-tolerance, one could end up in a situation
where one would keep aligning the written buffers behind the current
read-segment position. The result for the reader would be complete
silence, possible preceded by very choppy audio.

By checking the available headroom, one can determine if there is
room to do alignment, or if one should resort to a resync instead to get
the pointers back on track.

Also refactor the alignment-logic out of the render function for cleaner
code.
---
 gst-libs/gst/audio/gstbaseaudiosink.c | 75 ++++++++++++++++++---------
 1 file changed, 51 insertions(+), 24 deletions(-)

diff --git a/gst-libs/gst/audio/gstbaseaudiosink.c b/gst-libs/gst/audio/gstbaseaudiosink.c
index c0f6008f35..60930926bc 100644
--- a/gst-libs/gst/audio/gstbaseaudiosink.c
+++ b/gst-libs/gst/audio/gstbaseaudiosink.c
@@ -1319,6 +1319,56 @@ flushing:
   }
 }
 
+static gint64
+gst_base_audio_sink_get_alignment (GstBaseAudioSink * sink, GstClockTime sample_offset)
+{
+  GstRingBuffer *ringbuf = sink->ringbuffer;
+  gint64 align;
+  gint64 diff;
+  gint64 maxdrift;
+  gint segdone = g_atomic_int_get (&ringbuf->segdone) - ringbuf->segbase;
+  gint64 samples_done = segdone * ringbuf->samples_per_seg;
+  gint64 headroom = sample_offset - samples_done;
+  gboolean allow_align = TRUE;
+
+  /* now try to align the sample to the previous one, first see how big the
+   * difference is. */
+  if (sample_offset >= sink->next_sample)
+    diff = sample_offset - sink->next_sample;
+  else
+    diff = sink->next_sample - sample_offset;
+
+  /* calculate the max allowed drift in units of samples. By default this is
+   * 20ms and should be anough to compensate for timestamp rounding errors. */
+  maxdrift = (ringbuf->spec.rate * sink->priv->drift_tolerance) / GST_MSECOND;
+
+  /* calc align with previous sample */
+  align = sink->next_sample - sample_offset;
+
+  /* don't align if it means writing behind the read-segment */
+  if (diff > headroom && align < 0)
+    allow_align = FALSE;
+
+  if (G_LIKELY (diff < maxdrift && allow_align)) {
+    GST_DEBUG_OBJECT (sink,
+        "align with prev sample, ABS (%" G_GINT64_FORMAT ") < %"
+        G_GINT64_FORMAT, align, maxdrift);
+  } else {
+    /* calculate sample diff in seconds for error message */
+    gint64 diff_s = gst_util_uint64_scale_int (diff, GST_SECOND, ringbuf->spec.rate);
+    /* timestamps drifted apart from previous samples too much, we need to
+     * resync. We log this as an element warning. */
+    GST_WARNING_OBJECT (sink,
+        "Unexpected discontinuity in audio timestamps of "
+        "%s%" GST_TIME_FORMAT ", resyncing",
+        sample_offset > sink->next_sample ? "+" : "-",
+        GST_TIME_ARGS (diff_s));
+    align = 0;
+  }
+
+  return align;
+}
+
 static GstFlowReturn
 gst_base_audio_sink_render (GstBaseSink * bsink, GstBuffer * buf)
 {
@@ -1340,7 +1390,6 @@ gst_base_audio_sink_render (GstBaseSink * bsink, GstBuffer * buf)
   GstFlowReturn ret;
   GstSegment clip_seg;
   gint64 time_offset;
-  gint64 maxdrift;
 
   sink = GST_BASE_AUDIO_SINK (bsink);
 
@@ -1574,29 +1623,7 @@ gst_base_audio_sink_render (GstBaseSink * bsink, GstBuffer * buf)
     goto no_align;
   }
 
-  /* now try to align the sample to the previous one, first see how big the
-   * difference is. */
-  if (sample_offset >= sink->next_sample)
-    diff = sample_offset - sink->next_sample;
-  else
-    diff = sink->next_sample - sample_offset;
-
-  /* calculate the max allowed drift in units of samples. By default this is
-   * 20ms and should be anough to compensate for timestamp rounding errors. */
-  maxdrift = (ringbuf->spec.rate * sink->priv->drift_tolerance) / GST_MSECOND;
-
-  if (G_LIKELY (diff < maxdrift)) {
-    /* calc align with previous sample */
-    align = sink->next_sample - sample_offset;
-    GST_DEBUG_OBJECT (sink,
-        "align with prev sample, ABS (%" G_GINT64_FORMAT ") < %"
-        G_GINT64_FORMAT, align, maxdrift);
-  } else {
-    GST_DEBUG_OBJECT (sink,
-        "discont timestamp (%" G_GINT64_FORMAT ") >= %" G_GINT64_FORMAT, diff,
-        maxdrift);
-    align = 0;
-  }
+  align = gst_base_audio_sink_get_alignment (sink, sample_offset);
   sink->priv->last_align = align;
 
   /* apply alignment */