From 0e60076a390fd3ef53d350940b2c695ff7bbe008 Mon Sep 17 00:00:00 2001
From: =?utf8?q?Alicia=20Boya=20Garc=C3=ADa?= <aboya@igalia.com>
Date: Fri, 21 Sep 2018 20:38:02 +0200
Subject: [PATCH] matroskademux: Parse successive Tracks elements

This patch allows matroskademux to parse a second Tracks element,
erroring out if the tracks are not compatible (different number, type or
codec) and emitting new caps and tag events should they have changed.

https://bugzilla.gnome.org/show_bug.cgi?id=793333
---
 gst/matroska/matroska-demux.c | 111 +++++++++++++++++++++++++++++++++++++++++-
 1 file changed, 109 insertions(+), 2 deletions(-)

diff --git a/gst/matroska/matroska-demux.c b/gst/matroska/matroska-demux.c
index 0e2157a..77176fb 100644
--- a/gst/matroska/matroska-demux.c
+++ b/gst/matroska/matroska-demux.c
@@ -3132,6 +3132,113 @@ gst_matroska_demux_parse_tracks (GstMatroskaDemux * demux, GstEbmlRead * ebml)
   return ret;
 }
 
+static GstFlowReturn
+gst_matroska_demux_update_tracks (GstMatroskaDemux * demux, GstEbmlRead * ebml)
+{
+  GstFlowReturn ret = GST_FLOW_OK;
+  guint num_tracks_found = 0;
+  guint32 id;
+
+  GST_INFO_OBJECT (demux, "Reparsing Tracks element");
+
+  DEBUG_ELEMENT_START (demux, ebml, "Tracks");
+
+  if ((ret = gst_ebml_read_master (ebml, &id)) != GST_FLOW_OK) {
+    DEBUG_ELEMENT_STOP (demux, ebml, "Tracks", ret);
+    return ret;
+  }
+
+  while (ret == GST_FLOW_OK && gst_ebml_read_has_remaining (ebml, 1, TRUE)) {
+    if ((ret = gst_ebml_peek_id (ebml, &id)) != GST_FLOW_OK)
+      break;
+
+    switch (id) {
+        /* one track within the "all-tracks" header */
+      case GST_MATROSKA_ID_TRACKENTRY:{
+        GstMatroskaTrackContext *new_track;
+        gint old_track_index;
+        GstMatroskaTrackContext *old_track;
+        ret = gst_matroska_demux_parse_stream (demux, ebml, &new_track);
+        if (new_track == NULL)
+          break;
+        num_tracks_found++;
+
+        if (gst_matroska_read_common_tracknumber_unique (&demux->common,
+                new_track->num)) {
+          GST_ERROR_OBJECT (demux,
+              "Unexpected new TrackNumber: %" G_GUINT64_FORMAT, new_track->num);
+          goto track_mismatch_error;
+        }
+
+        old_track_index =
+            gst_matroska_read_common_stream_from_num (&demux->common,
+            new_track->num);
+        g_assert (old_track_index != -1);
+        old_track = g_ptr_array_index (demux->common.src, old_track_index);
+
+        if (old_track->type != new_track->type) {
+          GST_ERROR_OBJECT (demux,
+              "Mismatch reparsing track %" G_GUINT64_FORMAT
+              " on track type. Expected %d, found %d", new_track->num,
+              old_track->type, new_track->type);
+          goto track_mismatch_error;
+        }
+
+        if (g_strcmp0 (old_track->codec_id, new_track->codec_id) != 0) {
+          GST_ERROR_OBJECT (demux,
+              "Mismatch reparsing track %" G_GUINT64_FORMAT
+              " on codec id. Expected '%s', found '%s'", new_track->num,
+              old_track->codec_id, new_track->codec_id);
+          goto track_mismatch_error;
+        }
+
+        /* The new track matches the old track. No problems on our side.
+         * Let's make it replace the old track. */
+        new_track->pad = old_track->pad;
+        new_track->index = old_track->index;
+        new_track->pos = old_track->pos;
+        g_ptr_array_index (demux->common.src, old_track_index) = new_track;
+        gst_pad_set_element_private (new_track->pad, new_track);
+
+        if (!gst_caps_is_equal (old_track->caps, new_track->caps)) {
+          gst_pad_set_caps (new_track->pad, new_track->caps);
+        }
+
+        if (!gst_tag_list_is_equal (old_track->tags, new_track->tags)) {
+          GST_DEBUG_OBJECT (old_track->pad, "Sending tags %p: %"
+              GST_PTR_FORMAT, new_track->tags, new_track->tags);
+          gst_pad_push_event (new_track->pad,
+              gst_event_new_tag (gst_tag_list_copy (new_track->tags)));
+        }
+
+        gst_matroska_track_free (old_track);
+        break;
+
+      track_mismatch_error:
+        gst_matroska_track_free (new_track);
+        new_track = NULL;
+        ret = GST_FLOW_ERROR;
+        break;
+      }
+
+      default:
+        ret = gst_matroska_read_common_parse_skip (&demux->common, ebml,
+            "Track", id);
+        break;
+    }
+  }
+  DEBUG_ELEMENT_STOP (demux, ebml, "Tracks", ret);
+
+  if (ret != GST_FLOW_ERROR && demux->common.num_streams != num_tracks_found) {
+    GST_ERROR_OBJECT (demux,
+        "Mismatch on the number of tracks. Expected %du tracks, found %du",
+        demux->common.num_streams, num_tracks_found);
+    ret = GST_FLOW_ERROR;
+  }
+
+  return ret;
+}
+
 /*
  * Read signed/unsigned "EBML" numbers.
  * Return: number of bytes processed.
@@ -5031,11 +5138,11 @@ gst_matroska_demux_parse_id (GstMatroskaDemux * demux, guint32 id,
           }
           break;
         case GST_MATROSKA_ID_TRACKS:
+          GST_READ_CHECK (gst_matroska_demux_take (demux, read, &ebml));
           if (!demux->tracks_parsed) {
-            GST_READ_CHECK (gst_matroska_demux_take (demux, read, &ebml));
             ret = gst_matroska_demux_parse_tracks (demux, &ebml);
           } else {
-            GST_READ_CHECK (gst_matroska_demux_flush (demux, read));
+            ret = gst_matroska_demux_update_tracks (demux, &ebml);
           }
           break;
         case GST_MATROSKA_ID_CLUSTER:
-- 
2.7.4