mpegtsdemux: Add property to disable skew corrections

This is for cases where:
* We *do* want to refer to the PCR stream to figure out global positioning, gap
  detection, wrapover correction.
* But we do not want to apply any skew correction to the output

This is useful for cases where:
* the input stream has already been clock-corrected (for example with
mpegtslivesrc)
* or where the output doesn't require synchronization against a clock (ex: for
  storage)

Part-of: <https://gitlab.freedesktop.org/gstreamer/gstreamer/-/merge_requests/9301>

subprojects/gst-plugins-bad/docs/plugins/gst_plugins_cache.json

@@ -225993,6 +225993,18 @@
                         "readable": true,
                         "type": "gboolean",
                         "writable": true
+                    },
+                    "skew-corrections": {
+                        "blurb": "Apply skew corrections",
+                        "conditionally-available": false,
+                        "construct": false,
+                        "construct-only": false,
+                        "controllable": false,
+                        "default": "true",
+                        "mutable": "null",
+                        "readable": true,
+                        "type": "gboolean",
+                        "writable": true
                     }
                 }
             }

subprojects/gst-plugins-bad/gst/mpegtsdemux/mpegtsbase.c

@@ -60,13 +60,15 @@ static GstStaticPadTemplate sink_template = GST_STATIC_PAD_TEMPLATE ("sink",
     );
 
 #define DEFAULT_IGNORE_PCR FALSE
+#define DEFAULT_SKEW_CORRECTIONS TRUE
 
 enum
 {
   PROP_0,
   PROP_PARSE_PRIVATE_SECTIONS,
   PROP_IGNORE_PCR,
-  /* FILL ME */
+  PROP_SKEW_CORRECTIONS
+      /* FILL ME */
 };
 
 static void mpegts_base_dispose (GObject * object);
@@ -149,7 +151,7 @@ mpegts_base_class_init (MpegTSBaseClass * klass)
           G_PARAM_READWRITE | G_PARAM_STATIC_STRINGS));
 
   /**
-   * GstMpegtsBase:ignore-pcr:
+   * MpegTSBase:ignore-pcr:
    *
    * Ignore PCR (Program Clock Reference) data from MPEG-TS PSI.
    * This can help with playback of some broken files.
@@ -161,6 +163,20 @@ mpegts_base_class_init (MpegTSBaseClass * klass)
           "Ignore PCR stream for timing", DEFAULT_IGNORE_PCR,
           G_PARAM_READWRITE | G_PARAM_STATIC_STRINGS));
 
+  /**
+   * MpegTSBase:skew-corrections:
+   *
+   * With push TIME inputs, apply continuous skew corrections to the output. The
+   * default is enabled. You can disable it if downstream doesn't require live
+   * synchronization.
+   *
+   * Since: 1.28
+   */
+  g_object_class_install_property (gobject_class, PROP_SKEW_CORRECTIONS,
+      g_param_spec_boolean ("skew-corrections", "Apply skew corrections",
+          "Apply skew corrections", DEFAULT_SKEW_CORRECTIONS,
+          G_PARAM_READWRITE | G_PARAM_STATIC_STRINGS));
+
   klass->sink_query = GST_DEBUG_FUNCPTR (mpegts_base_default_sink_query);
   klass->handle_psi = NULL;
 
@@ -180,6 +196,9 @@ mpegts_base_set_property (GObject * object, guint prop_id,
     case PROP_IGNORE_PCR:
       base->ignore_pcr = g_value_get_boolean (value);
       break;
+    case PROP_SKEW_CORRECTIONS:
+      base->packetizer->skew_correction = g_value_get_boolean (value);
+      break;
     default:
       G_OBJECT_WARN_INVALID_PROPERTY_ID (object, prop_id, pspec);
   }
@@ -198,6 +217,9 @@ mpegts_base_get_property (GObject * object, guint prop_id,
     case PROP_IGNORE_PCR:
       g_value_set_boolean (value, base->ignore_pcr);
       break;
+    case PROP_SKEW_CORRECTIONS:
+      g_value_set_boolean (value, base->packetizer->skew_correction);
+      break;
     default:
       G_OBJECT_WARN_INVALID_PROPERTY_ID (object, prop_id, pspec);
   }
@@ -269,6 +291,7 @@ mpegts_base_init (MpegTSBase * base)
 
   base->disposed = FALSE;
   base->packetizer = mpegts_packetizer_new ();
+  base->packetizer->skew_correction = DEFAULT_SKEW_CORRECTIONS;
   base->programs =
       g_ptr_array_new_full (16, (GDestroyNotify) mpegts_base_free_program);
 

subprojects/gst-plugins-bad/gst/mpegtsdemux/mpegtspacketizer.c

@@ -1471,6 +1471,9 @@ calculate_skew (MpegTSPacketizer2 * packetizer,
   /* keep track of the last extended pcrtime */
   pcr->last_pcrtime = gstpcrtime;
 
+  if (!packetizer->skew_correction)
+    goto no_skew;
+
   /* we don't have an arrival timestamp so we can't do skew detection. we
    * should still apply a timestamp based on RTP timestamp and base_time */
   if (!GST_CLOCK_TIME_IS_VALID (time)

subprojects/gst-plugins-bad/gst/mpegtsdemux/mpegtspacketizer.h

@@ -259,6 +259,8 @@ struct _MpegTSPacketizer2 {
 
   /* clock skew calculation */
   gboolean       calculate_skew;
+  /* skew_correction: apply skew correction to values */
+  gboolean       skew_correction;
 
   /* offset/bitrate calculator */
   gboolean       calculate_offset;