qtmux: properly support initial caps nego failure

Scenario:
- gap event causes h264parse to push made up caps that may fail checks
  inside qtmux (e.g missing codec_data).
- the caps event has already been marked as received and is sticky on
  the sink pad
- gst_qt_mux_pad_can_renegotiate() will retrieve the failed caps event
  using gst_pad_get_current_caps() and reject the correct updated caps
  with codec_data.
- Failure!

Keep track of the configured caps ourselves instead of relying on the
sticky event on the pad.

Part-of: <https://gitlab.freedesktop.org/gstreamer/gst-plugins-good/-/merge_requests/732>

gst/isomp4/gstqtmux.c

@@ -660,6 +660,8 @@ gst_qt_mux_pad_reset (GstQTMuxPad * qtpad)
 
   gst_buffer_replace (&qtpad->last_buf, NULL);
 
+  gst_caps_replace (&qtpad->configured_caps, NULL);
+
   if (qtpad->tags) {
     gst_tag_list_unref (qtpad->tags);
     qtpad->tags = NULL;
@@ -5569,7 +5571,8 @@ find_best_pad (GstQTMux * qtmux)
     gboolean push_stored = FALSE;
 
     GST_OBJECT_LOCK (qtmux);
-    if (GST_ELEMENT (qtmux)->sinkpads->next || qtmux->force_chunks) {
+    if ((GST_ELEMENT (qtmux)->sinkpads && GST_ELEMENT (qtmux)->sinkpads->next)
+        || qtmux->force_chunks) {
       /* Only switch pads if we have more than one, otherwise
        * we can just put everything into a single chunk and save
        * a few bytes of offsets.
@@ -5734,30 +5737,30 @@ gst_qtmux_caps_is_subset_full (GstQTMux * qtmux, GstCaps * subset,
 static gboolean
 gst_qt_mux_can_renegotiate (GstQTMux * qtmux, GstPad * pad, GstCaps * caps)
 {
-  GstCaps *current_caps;
+  GstQTMuxPad *qtmuxpad = GST_QT_MUX_PAD_CAST (pad);
 
   /* does not go well to renegotiate stream mid-way, unless
    * the old caps are a subset of the new one (this means upstream
    * added more info to the caps, as both should be 'fixed' caps) */
-  current_caps = gst_pad_get_current_caps (pad);
 
-  if (!current_caps)
+  if (!qtmuxpad->configured_caps) {
+    GST_DEBUG_OBJECT (qtmux, "pad %s accepted caps %" GST_PTR_FORMAT,
+        GST_PAD_NAME (pad), caps);
     return TRUE;
+  }
 
   g_assert (caps != NULL);
 
-  if (!gst_qtmux_caps_is_subset_full (qtmux, current_caps, caps)) {
-    gst_caps_unref (current_caps);
+  if (!gst_qtmux_caps_is_subset_full (qtmux, qtmuxpad->configured_caps, caps)) {
     GST_WARNING_OBJECT (qtmux,
-        "pad %s refused renegotiation to %" GST_PTR_FORMAT,
-        GST_PAD_NAME (pad), caps);
+        "pad %s refused renegotiation to %" GST_PTR_FORMAT " from %"
+        GST_PTR_FORMAT, GST_PAD_NAME (pad), caps, qtmuxpad->configured_caps);
     return FALSE;
   }
 
   GST_DEBUG_OBJECT (qtmux,
       "pad %s accepted renegotiation to %" GST_PTR_FORMAT " from %"
-      GST_PTR_FORMAT, GST_PAD_NAME (pad), caps, current_caps);
-  gst_caps_unref (current_caps);
+      GST_PTR_FORMAT, GST_PAD_NAME (pad), caps, qtmuxpad->configured_caps);
 
   return TRUE;
 }
@@ -6827,6 +6830,10 @@ gst_qt_mux_sink_event (GstAggregator * agg, GstAggregatorPad * agg_pad,
       g_assert (qtmux_pad->set_caps);
 
       ret = qtmux_pad->set_caps (qtmux_pad, caps);
+
+      if (ret)
+        gst_caps_replace (&qtmux_pad->configured_caps, caps);
+
       gst_event_unref (event);
       event = NULL;
       break;
@@ -6893,9 +6900,12 @@ static void
 gst_qt_mux_release_pad (GstElement * element, GstPad * pad)
 {
   GstQTMux *mux = GST_QT_MUX_CAST (element);
+  GstQTMuxPad *muxpad = GST_QT_MUX_PAD_CAST (pad);
 
   GST_DEBUG_OBJECT (element, "Releasing %s:%s", GST_DEBUG_PAD_NAME (pad));
 
+  gst_qt_mux_pad_reset (muxpad);
+
   gst_element_remove_pad (element, pad);
 
   if (mux->current_pad && GST_PAD (mux->current_pad) == pad) {

gst/isomp4/gstqtmux.h

@@ -177,6 +177,8 @@ struct _GstQTMuxPad
   guint64 raw_audio_adapter_offset;
   GstClockTime raw_audio_adapter_pts;
   GstFlowReturn flow_status;
+
+  GstCaps *configured_caps;
 };
 
 struct _GstQTMuxPadClass

tests/check/elements/qtmux.c

@@ -27,6 +27,7 @@
 #include <glib/gstdio.h>
 
 #include <gst/check/gstcheck.h>
+#include <gst/check/gstharness.h>
 #include <gst/pbutils/encoding-profile.h>
 
 /* For ease of programming we use globals to keep refs for our floating
@@ -1806,6 +1807,52 @@ GST_START_TEST (test_muxing_initial_gap)
 
 GST_END_TEST;
 
+GST_START_TEST (test_caps_renego)
+{
+  GstHarness *h;
+  GstBuffer *buf;
+  GstCaps *caps;
+  GstSegment segment;
+  GstPad *pad;
+
+  h = gst_harness_new_with_padnames ("qtmux", "video_0", "src");
+  /* appease the harness */
+  pad = gst_element_get_static_pad (h->element, "video_0");
+
+  fail_unless (gst_harness_push_event (h,
+          gst_event_new_stream_start ("random")));
+
+  /* caps event with not enough information, should probably fail but
+   * currently only does from aggregate() */
+  caps = gst_caps_from_string
+      ("video/x-h264, stream-format=(string)avc, alignment=(string)au, width=(int)16, height=(int)16");
+  fail_unless (gst_harness_push_event (h, gst_event_new_caps (caps)));
+  gst_caps_unref (caps);
+  /* subsequent caps event with enough information should succeed */
+  caps = gst_caps_from_string
+      ("video/x-h264, width=(int)800, height=(int)600, "
+      "framerate=(fraction)1/1, stream-format=(string)avc, codec_data=(buffer)0000,"
+      " alignment=(string)au, level=(int)2, profile=(string)high");
+  fail_unless (gst_harness_push_event (h, gst_event_new_caps (caps)));
+  gst_caps_unref (caps);
+  gst_segment_init (&segment, GST_FORMAT_TIME);
+  fail_unless (gst_harness_push_event (h, gst_event_new_segment (&segment)));
+
+  buf = create_buffer (0 * GST_SECOND, 0, GST_SECOND, 4096);
+  fail_unless_equals_int (GST_FLOW_OK, gst_harness_push (h, buf));
+
+  fail_unless (gst_harness_push_event (h, gst_event_new_eos ()));
+
+  buf = gst_harness_pull (h);
+  fail_unless (buf != NULL);
+  gst_buffer_unref (buf);
+
+  gst_harness_teardown (h);
+  gst_object_unref (pad);
+}
+
+GST_END_TEST;
+
 static Suite *
 qtmux_suite (void)
 {
@@ -1852,6 +1899,8 @@ qtmux_suite (void)
   tcase_add_test (tc_chain, test_muxing_dts_outside_segment);
   tcase_add_test (tc_chain, test_muxing_initial_gap);
 
+  tcase_add_test (tc_chain, test_caps_renego);
+
   return s;
 }