qtdemux: improve fragment-start tracking

Some buffers can have multiple moov atoms inside and the strategy
of using the gst_adapter_prev_pts timestamp to get the base timestamp
for the media of the fragment would fail as it would reuse the same
base timestamp for all moofs in the buffer instead of accumulating
the durations for all of them.

Heres a better explanation of the issue:
qtdemux receives a buffer where PTS(buf) = X
buf -> moofA | moofB | moofC

The problem was that PTS(buf) was used as the base timestamp for
all 3 moofs, causing all buffers to be X based. In this case we want
only moofA to be X based as it is what the PTS on buf means, and the
other moofB and moofC just use the accumulated timestamp from the
previous moofs durations.

To solve this, this patch uses gst_adapter_prev_pts distance
result, this allows qtdemux to calculate if it should use the
resulting pts or just accumulate the samples as it can identify
if the moofs belong to the same upstream buffer or not.

https://bugzilla.gnome.org/show_bug.cgi?id=719783

diff --git a/gst/isomp4/qtdemux.c b/gst/isomp4/qtdemux.c
index d2ca3f4f65df8a4ecc79fb1162f74fd143b4639c..72000a9507265a6f1453860e38abe4231552fee3 100644 (file)
--- a/gst/isomp4/qtdemux.c
+++ b/gst/isomp4/qtdemux.c
@@ -537,6 +537,7 @@ gst_qtdemux_init (GstQTDemux * qtdemux)
   qtdemux->restoredata_buffer = NULL;
   qtdemux->restoredata_offset = GST_CLOCK_TIME_NONE;
   qtdemux->fragment_start = -1;
+  qtdemux->fragment_start_offset = -1;
   qtdemux->media_caps = NULL;
   qtdemux->exposed = FALSE;
   qtdemux->mss_mode = FALSE;
@@ -1841,6 +1842,7 @@ gst_qtdemux_reset (GstQTDemux * qtdemux, gboolean hard)
     qtdemux->upstream_size = 0;
 
     qtdemux->fragment_start = -1;
+    qtdemux->fragment_start_offset = -1;
     qtdemux->duration = 0;
     qtdemux->mfra_offset = 0;
     qtdemux->moof_offset = 0;
@@ -4592,18 +4594,8 @@ gst_qtdemux_chain (GstPad * sinkpad, GstObject * parent, GstBuffer * inbuf)
 {
   GstQTDemux *demux;
   GstFlowReturn ret = GST_FLOW_OK;
-  GstClockTime timestamp;
-
   demux = GST_QTDEMUX (parent);
 
-  timestamp = GST_BUFFER_TIMESTAMP (inbuf);
-
-  if (G_UNLIKELY (GST_CLOCK_TIME_IS_VALID (timestamp))) {
-    demux->fragment_start = timestamp;
-    GST_DEBUG_OBJECT (demux, "got fragment_start %" GST_TIME_FORMAT,
-        GST_TIME_ARGS (timestamp));
-  }
-
   gst_adapter_push (demux->adapter, inbuf);
 
   /* we never really mean to buffer that much */
@@ -4786,11 +4778,35 @@ gst_qtdemux_chain (GstPad * sinkpad, GstObject * parent, GstBuffer * inbuf)
           }
         } else if (fourcc == FOURCC_moof) {
           if ((demux->got_moov || demux->media_caps) && demux->fragmented) {
+            guint64 dist = 0;
+            GstClockTime prev_pts;
+            guint64 prev_offset;
+
             GST_DEBUG_OBJECT (demux, "Parsing [moof]");
 
-            /* the timestamp of the moof buffer is relevant as some scenarios
-             * won't have the initial timestamp in the atoms */
-            demux->fragment_start = gst_adapter_prev_pts (demux->adapter, NULL);
+            /*
+             * The timestamp of the moof buffer is relevant as some scenarios
+             * won't have the initial timestamp in the atoms. Whenever a new
+             * buffer has started, we get that buffer's PTS and use it as a base
+             * timestamp for the trun entries.
+             *
+             * To keep track of the current buffer timestamp and starting point
+             * we use gst_adapter_prev_pts that gives us the PTS and the distance
+             * from the beggining of the buffer, with the distance and demux->offset
+             * we know if it is still the same buffer or not.
+             */
+            prev_pts = gst_adapter_prev_pts (demux->adapter, &dist);
+            prev_offset = demux->offset - dist;
+            if (demux->fragment_start_offset == -1
+                || prev_offset > demux->fragment_start_offset) {
+              demux->fragment_start_offset = prev_offset;
+              demux->fragment_start = prev_pts;
+              GST_DEBUG_OBJECT (demux,
+                  "New fragment start found at: %" G_GUINT64_FORMAT " : %"
+                  GST_TIME_FORMAT, demux->fragment_start_offset,
+                  GST_TIME_ARGS (demux->fragment_start));
+            }
+
             if (!qtdemux_parse_moof (demux, data, demux->neededbytes,
                     demux->offset, NULL)) {
               gst_adapter_unmap (demux->adapter);

diff --git a/gst/isomp4/qtdemux.h b/gst/isomp4/qtdemux.h
index a6b9768f58b50481d44dcad113476c8ea3ea7399..e6cc769f3d1182b93c902da71ebd2a37c962f2c9 100644 (file)
--- a/gst/isomp4/qtdemux.h
+++ b/gst/isomp4/qtdemux.h
@@ -134,6 +134,7 @@ struct _GstQTDemux {
   gboolean exposed;
   gboolean mss_mode; /* flag to indicate that we're working with a smoothstreaming fragment */
   guint64 fragment_start;
+  guint64 fragment_start_offset;
     
   gint64 chapters_track_id;