ass: add ass_set_check_readorder() API function

Not all API users will keep the event list on seeking. This also gives
the opportunity to API users to handle severely broken files with
duplicate ReadOrder entries. (It is not known whether this is really
needed, however VSFilter does not deduplicate using the ReadOrder
field.)

3 files changed, 22 insertions, 3 deletions

diff --git a/libass/ass.c b/libass/ass.c
index 6cfa361..14264dc 100644
--- a/libass/ass.c
+++ b/libass/ass.c
@@ -57,6 +57,7 @@ struct parser_priv {
     // contains bitmap of ReadOrder IDs of all read events
     uint32_t *read_order_bitmap;
     int read_order_elems; // size in uint32_t units of read_order_bitmap
+    int check_readorder;
 };
 
 #define ASS_STYLES_ALLOC 20
@@ -899,6 +900,11 @@ static int check_duplicate_event(ASS_Track *track, int ReadOrder)
     return 0;
 }
 
+void ass_set_check_readorder(ASS_Track *track, int check_readorder)
+{
+    track->parser_priv->check_readorder = check_readorder == 1;
+}
+
 /**
  * \brief Process a chunk of subtitle stream data. In Matroska, this contains exactly 1 event (or a commentary).
  * \param track track
@@ -915,8 +921,9 @@ void ass_process_chunk(ASS_Track *track, char *data, int size,
     char *p;
     char *token;
     ASS_Event *event;
+    int check_readorder = track->parser_priv->check_readorder;
 
-    if (!track->parser_priv->read_order_bitmap) {
+    if (check_readorder && !track->parser_priv->read_order_bitmap) {
         for (int i = 0; i < track->n_events; i++) {
             if (test_and_set_read_order_bit(track, track->events[i].ReadOrder) < 0)
                 break;
@@ -944,7 +951,7 @@ void ass_process_chunk(ASS_Track *track, char *data, int size,
     do {
         NEXT(p, token);
         event->ReadOrder = atoi(token);
-        if (check_duplicate_event(track, event->ReadOrder))
+        if (check_readorder && check_duplicate_event(track, event->ReadOrder))
             break;
 
         NEXT(p, token);
@@ -1332,6 +1339,7 @@ ASS_Track *ass_new_track(ASS_Library *library)
         free(track);
         return NULL;
     }
+    track->parser_priv->check_readorder = 1;
     return track;
 }
 
diff --git a/libass/ass.h b/libass/ass.h
index c2802f7..bafbe8a 100644
--- a/libass/ass.h
+++ b/libass/ass.h
@@ -24,7 +24,7 @@
 #include <stdarg.h>
 #include "ass_types.h"
 
-#define LIBASS_VERSION 0x01301000
+#define LIBASS_VERSION 0x01302000
 
 #ifdef __cplusplus
 extern "C" {
@@ -577,6 +577,16 @@ void ass_process_chunk(ASS_Track *track, char *data, int size,
                        long long timecode, long long duration);
 
 /**
+ * \brief Set whether the ReadOrder field when processing a packet with
+ * ass_process_chunk() should be used for eliminating duplicates.
+ * \param check_readorder 0 means do not try to eliminate duplicates; 1 means
+ * use the ReadOrder field embedded in the packet as unique identifier, and
+ * discard the packet if there was already a packet with the same ReadOrder.
+ * Other values are undefined.
+ */
+void ass_set_check_readorder(ASS_Track *track, int check_readorder);
+
+/**
  * \brief Flush buffered events.
  * \param track track
 */
diff --git a/libass/libass.sym b/libass/libass.sym
index 5cdca1f..42ca0cd 100644
--- a/libass/libass.sym
+++ b/libass/libass.sym
@@ -42,3 +42,4 @@ ass_set_line_position
 ass_set_pixel_aspect
 ass_set_selective_style_override_enabled
 ass_set_selective_style_override
+ass_set_check_readorder