deinterlace: Add support for deinterlacing using buffer caps/flags

When not using the fieldanalysis element immediately upstream of deinterlace,
behaviour should remain unchanged. fieldanalysis will set the caps and flags on
the buffers such that they can be interpreted and acted upon to produce
progressive output.

There are two main modes of operation:

- Passive pattern locking
  Passive pattern locking is a non-blocking, low-latency mode of operation that
  is suitable for close-to-live usage. Initially a telecine stream will be
  output as variable framerate with naïve timestamp adjustment. With each
  incoming buffer, an attempt is made to lock onto a pattern. When a lock is
  obtained, the src pad and output buffer caps will reflect the pattern and
  timestamps will be accurately interpolated between pattern repeats. This
  means that initially and at pattern transitions there will be short periods
  of inaccurate timestamping.

- Active pattern locking
  Active pattern locking is a blocking, high-latency mode of operation that is
  targeted at use-cases where timestamp accuracy is paramount. Buffers will be
  queued until enough are present to make a lock. When locked, timestamps will
  be accurately interpolated between pattern repeats. Orphan fields can be
  dropped or deinterlaced. If no lock can be obtained, a single field might be
  pushed through to be deinterlaced.

Locking can also be disabled or 'auto' chooses between passive and active
locking modes depending on whether upstream is live.

gst/deinterlace/gstdeinterlace.h

@@ -43,8 +43,6 @@ G_BEGIN_DECLS
 typedef struct _GstDeinterlace GstDeinterlace;
 typedef struct _GstDeinterlaceClass GstDeinterlaceClass;
 
-#define GST_DEINTERLACE_MAX_FIELD_HISTORY 10
-
 typedef enum
 {
   GST_DEINTERLACE_TOMSMOCOMP,
@@ -79,6 +77,39 @@ typedef enum {
   GST_DEINTERLACE_MODE_DISABLED
 } GstDeinterlaceMode;
 
+typedef enum
+{
+  GST_DEINTERLACE_LOCKING_NONE,
+  GST_DEINTERLACE_LOCKING_AUTO,
+  GST_DEINTERLACE_LOCKING_ACTIVE,
+  GST_DEINTERLACE_LOCKING_PASSIVE,
+} GstDeinterlaceLocking;
+
+#define GST_DEINTERLACE_MAX_FIELD_HISTORY 10
+#define GST_DEINTERLACE_MAX_BUFFER_STATE_HISTORY 50
+/* check max field history is large enough */
+#if GST_DEINTERLACE_MAX_FIELD_HISTORY < GST_DEINTERLACE_MAX_BUFFER_STATE_HISTORY * 3
+#undef GST_DEINTERLACE_MAX_FIELD_HISTORY
+#define GST_DEINTERLACE_MAX_FIELD_HISTORY (GST_DEINTERLACE_MAX_BUFFER_STATE_HISTORY * 3)
+#endif
+
+typedef struct _TelecinePattern TelecinePattern;
+struct _TelecinePattern
+{
+  const gchar *nick;
+  guint8 length;
+  guint8 ratio_n, ratio_d;
+  guint8 states[GST_DEINTERLACE_MAX_BUFFER_STATE_HISTORY];
+};
+
+typedef struct _GstDeinterlaceBufferState GstDeinterlaceBufferState;
+struct _GstDeinterlaceBufferState
+{
+  GstClockTime timestamp;
+  GstClockTime duration;
+  guint8 state;
+};
+
 struct _GstDeinterlace
 {
   GstElement parent;
@@ -92,8 +123,10 @@ struct _GstDeinterlace
 
   GstDeinterlaceFields fields;
 
-  GstDeinterlaceMethods method_id; /* current state (differs when flushing) */
-  GstDeinterlaceMethods user_set_method_id; /* property value */
+  /* current state (differs when flushing/inverse telecine using weave) */
+  GstDeinterlaceMethods method_id;
+  /* property value */
+  GstDeinterlaceMethods user_set_method_id;
   GstDeinterlaceMethod *method;
 
   GstVideoFormat format;
@@ -134,6 +167,24 @@ struct _GstDeinterlace
   gboolean reconfigure;
   GstDeinterlaceMode new_mode;
   GstDeinterlaceFields new_fields;
+
+  GstDeinterlaceLocking locking;
+  gint low_latency;
+  gboolean drop_orphans;
+  gboolean ignore_obscure;
+  gboolean pattern_lock;
+  gboolean pattern_refresh;
+  GstDeinterlaceBufferState buf_states[GST_DEINTERLACE_MAX_BUFFER_STATE_HISTORY];
+  gint state_count;
+  gint pattern;
+  guint8 pattern_phase;
+  guint8 pattern_count;
+  guint8 output_count;
+  GstClockTime pattern_base_ts;
+  GstClockTime pattern_buf_dur;
+
+  gboolean need_more;
+  gboolean have_eos;
 };
 
 struct _GstDeinterlaceClass