adaptivedemux: track per-fragment bitrates.

And use the average to go up in resolution, and the last fragment
bitrate to go down.

This allows the demuxer to react rapidly to bitrate loss, and
be conservative for bitrate improvements.

+ Add a construct only property to define the number of fragments
  to consider when calculating the average moving bitrate.

https://bugzilla.gnome.org/show_bug.cgi?id=742979

2 files changed, 113 insertions, 20 deletions

diff --git a/gst-libs/gst/adaptivedemux/gstadaptivedemux.c b/gst-libs/gst/adaptivedemux/gstadaptivedemux.c
index dcf16aaf3..6568110c3 100644
--- a/gst-libs/gst/adaptivedemux/gstadaptivedemux.c
+++ b/gst-libs/gst/adaptivedemux/gstadaptivedemux.c
@@ -86,6 +86,14 @@ GST_DEBUG_CATEGORY (adaptivedemux_debug);
 
 #define MAX_DOWNLOAD_ERROR_COUNT 3
 #define DEFAULT_FAILED_COUNT 3
+#define DEFAULT_LOOKBACK_FRAGMENTS 3
+
+enum
+{
+  PROP_0,
+  PROP_LOOKBACK_FRAGMENTS,
+  PROP_LAST
+};
 
 enum GstAdaptiveDemuxFlowReturn
 {
@@ -210,6 +218,38 @@ gst_adaptive_demux_get_type (void)
 }
 
 static void
+gst_adaptive_demux_set_property (GObject * object, guint prop_id,
+    const GValue * value, GParamSpec * pspec)
+{
+  GstAdaptiveDemux *demux = GST_ADAPTIVE_DEMUX (object);
+
+  switch (prop_id) {
+    case PROP_LOOKBACK_FRAGMENTS:
+      demux->num_lookback_fragments = g_value_get_uint (value);
+      break;
+    default:
+      G_OBJECT_WARN_INVALID_PROPERTY_ID (object, prop_id, pspec);
+      break;
+  }
+}
+
+static void
+gst_adaptive_demux_get_property (GObject * object, guint prop_id,
+    GValue * value, GParamSpec * pspec)
+{
+  GstAdaptiveDemux *demux = GST_ADAPTIVE_DEMUX (object);
+
+  switch (prop_id) {
+    case PROP_LOOKBACK_FRAGMENTS:
+      g_value_set_uint (value, demux->num_lookback_fragments);
+      break;
+    default:
+      G_OBJECT_WARN_INVALID_PROPERTY_ID (object, prop_id, pspec);
+      break;
+  }
+}
+
+static void
 gst_adaptive_demux_class_init (GstAdaptiveDemuxClass * klass)
 {
   GObjectClass *gobject_class;
@@ -226,8 +266,17 @@ gst_adaptive_demux_class_init (GstAdaptiveDemuxClass * klass)
   parent_class = g_type_class_peek_parent (klass);
   g_type_class_add_private (klass, sizeof (GstAdaptiveDemuxPrivate));
 
+  gobject_class->set_property = gst_adaptive_demux_set_property;
+  gobject_class->get_property = gst_adaptive_demux_get_property;
   gobject_class->finalize = gst_adaptive_demux_finalize;
 
+  g_object_class_install_property (gobject_class, PROP_LOOKBACK_FRAGMENTS,
+      g_param_spec_uint ("num-lookback-fragments",
+          "Number of fragments to look back",
+          "The number of fragments the demuxer will look back to calculate an average bitrate",
+          1, G_MAXUINT, DEFAULT_LOOKBACK_FRAGMENTS,
+          G_PARAM_READWRITE | G_PARAM_STATIC_STRINGS | G_PARAM_CONSTRUCT_ONLY));
+
   gstelement_class->change_state = gst_adaptive_demux_change_state;
 
   gstbin_class->handle_message = gst_adaptive_demux_handle_message;
@@ -274,6 +323,8 @@ gst_adaptive_demux_init (GstAdaptiveDemux * demux,
   gst_pad_set_chain_function (demux->sinkpad,
       GST_DEBUG_FUNCPTR (gst_adaptive_demux_sink_chain));
 
+  demux->num_lookback_fragments = DEFAULT_LOOKBACK_FRAGMENTS;
+
   gst_element_add_pad (GST_ELEMENT (demux), demux->sinkpad);
 }
 
@@ -702,6 +753,8 @@ gst_adaptive_demux_stream_new (GstAdaptiveDemux * demux, GstPad * pad)
 
   stream->pad = pad;
   stream->demux = demux;
+  stream->fragment_bitrates =
+      g_malloc0 (sizeof (guint64) * demux->num_lookback_fragments);
   gst_pad_set_element_private (pad, stream);
 
   gst_pad_set_query_function (pad,
@@ -766,6 +819,8 @@ gst_adaptive_demux_stream_free (GstAdaptiveDemuxStream * stream)
   g_cond_clear (&stream->fragment_download_cond);
   g_mutex_clear (&stream->fragment_download_lock);
 
+  g_free (stream->fragment_bitrates);
+
   if (stream->pad) {
     gst_object_unref (stream->pad);
     stream->pad = NULL;
@@ -1165,26 +1220,47 @@ gst_adaptive_demux_stream_set_tags (GstAdaptiveDemuxStream * stream,
 }
 
 static guint64
-gst_adaptive_demux_stream_update_current_bitrate (GstAdaptiveDemuxStream *
-    stream)
+_update_average_bitrate (GstAdaptiveDemux * demux,
+    GstAdaptiveDemuxStream * stream, guint64 new_bitrate)
+{
+  gint index = stream->moving_index % demux->num_lookback_fragments;
+
+  stream->moving_bitrate -= stream->fragment_bitrates[index];
+  stream->fragment_bitrates[index] = new_bitrate;
+  stream->moving_bitrate += new_bitrate;
+
+  stream->moving_index += 1;
+
+  if (stream->moving_index > demux->num_lookback_fragments)
+    return stream->moving_bitrate / demux->num_lookback_fragments;
+  return stream->moving_bitrate / stream->moving_index;
+}
+
+static guint64
+gst_adaptive_demux_stream_update_current_bitrate (GstAdaptiveDemux * demux,
+    GstAdaptiveDemuxStream * stream)
 {
-  guint64 bitrate = 0;
-
-  if (stream->download_total_time)
-    bitrate =
-        (stream->download_total_bytes * 8) /
-        ((double) stream->download_total_time / G_GUINT64_CONSTANT (1000000));
-
-  if (stream->current_download_rate != -1)
-    bitrate = (stream->current_download_rate + bitrate * 3) / 4;
-  if (bitrate > G_MAXINT)
-    bitrate = G_MAXINT;
-  stream->current_download_rate = bitrate;
-  GST_DEBUG_OBJECT (stream->pad, "Bitrate: %" G_GUINT64_FORMAT
-      " (bytes: %" G_GINT64_FORMAT " / %" G_GINT64_FORMAT " microsecs",
-      bitrate, stream->download_total_bytes, stream->download_total_time);
-
-  return bitrate;
+  guint64 average_bitrate;
+  guint64 fragment_bitrate;
+
+  fragment_bitrate =
+      (stream->fragment_total_size * 8) /
+      ((double) stream->fragment_total_time / G_GUINT64_CONSTANT (1000000));
+  stream->fragment_total_size = 0;
+  stream->fragment_total_time = 0;
+
+  average_bitrate = _update_average_bitrate (demux, stream, fragment_bitrate);
+
+  GST_INFO_OBJECT (stream, "last fragment bitrate was %" G_GUINT64_FORMAT,
+      fragment_bitrate);
+  GST_INFO_OBJECT (stream,
+      "Last %u fragments average bitrate is %" G_GUINT64_FORMAT,
+      demux->num_lookback_fragments, average_bitrate);
+
+  /* Conservative approach, make sure we don't upgrade too fast */
+  stream->current_download_rate = MIN (average_bitrate, fragment_bitrate);
+
+  return stream->current_download_rate;
 }
 
 static GstFlowReturn
@@ -1337,6 +1413,10 @@ _src_chain (GstPad * pad, GstObject * parent, GstBuffer * buffer)
       g_get_monotonic_time () - stream->download_chunk_start_time;
   stream->download_total_bytes += gst_buffer_get_size (buffer);
 
+  stream->fragment_total_size += gst_buffer_get_size (buffer);
+  stream->fragment_total_time +=
+      g_get_monotonic_time () - stream->download_chunk_start_time;
+
   gst_adapter_push (stream->adapter, buffer);
   GST_DEBUG_OBJECT (stream->pad, "Received buffer of size %" G_GSIZE_FORMAT
       ". Now %" G_GSIZE_FORMAT " on adapter", gst_buffer_get_size (buffer),
@@ -2229,6 +2309,8 @@ gst_adaptive_demux_stream_advance_fragment_unlocked (GstAdaptiveDemux * demux,
   g_clear_error (&stream->last_error);
   stream->download_total_time +=
       g_get_monotonic_time () - stream->download_chunk_start_time;
+  stream->fragment_total_time +=
+      g_get_monotonic_time () - stream->download_chunk_start_time;
 
   /* FIXME - url has no indication of byte ranges for subsegments */
   gst_element_post_message (GST_ELEMENT_CAST (demux),
@@ -2253,7 +2335,7 @@ gst_adaptive_demux_stream_advance_fragment_unlocked (GstAdaptiveDemux * demux,
 
   if (ret == GST_FLOW_OK) {
     if (gst_adaptive_demux_stream_select_bitrate (demux, stream,
-            gst_adaptive_demux_stream_update_current_bitrate (stream))) {
+            gst_adaptive_demux_stream_update_current_bitrate (demux, stream))) {
       stream->need_header = TRUE;
       gst_adapter_clear (stream->adapter);
       ret = (GstFlowReturn) GST_ADAPTIVE_DEMUX_FLOW_SWITCH;
diff --git a/gst-libs/gst/adaptivedemux/gstadaptivedemux.h b/gst-libs/gst/adaptivedemux/gstadaptivedemux.h
index 456d093dc..635aa1b82 100644
--- a/gst-libs/gst/adaptivedemux/gstadaptivedemux.h
+++ b/gst-libs/gst/adaptivedemux/gstadaptivedemux.h
@@ -144,6 +144,15 @@ struct _GstAdaptiveDemuxStream
   gint64 download_total_bytes;
   gint current_download_rate;
 
+  /* Per fragment download information */
+  guint64 fragment_total_time;
+  guint64 fragment_total_size;
+
+  /* Average for the last fragments */
+  guint64 moving_bitrate;
+  guint moving_index;
+  guint64 *fragment_bitrates;
+
   GstAdaptiveDemuxStreamFragment fragment;
 
   guint download_error_count;
@@ -182,6 +191,8 @@ struct _GstAdaptiveDemux
   gchar *manifest_uri;
   gchar *manifest_base_uri;
 
+  guint num_lookback_fragments;
+
   gboolean have_group_id;
   guint group_id;
 };