core: track current chapter for relative chapter seeks

Due to inexact seeks, chapter seek commands may result in a playback
position that's inside the previous chapter. This causes problems when
the user does repeated next-chapter/previous-chapter seeks, because
the code will use the wrong base for calculating 'next' or
'previous'. Improve the behavior by adding a heuristic that keeps
track of what chapter the user last wanted to seek to and adjusts the
"current chapter" value based on that.

1 files changed, 6 insertions, 0 deletions

diff --git a/mp_core.h b/mp_core.h
index 5c0b48d285..1a01109307 100644
--- a/mp_core.h
+++ b/mp_core.h
@@ -154,6 +154,12 @@ typedef struct MPContext {
     double rel_seek_secs;
     int abs_seek_pos;
 
+    /* Heuristic for relative chapter seeks: keep track which chapter
+     * the user wanted to go to, even if we aren't exactly within the
+     * boundaries of that chapter due to an inaccurate seek. */
+    int last_chapter_seek;
+    double last_chapter_pts;
+
     float begin_skip; ///< start time of the current skip while on edlout mode
     // audio is muted if either EDL or user activates mute
     short edl_muted; ///< Stores whether EDL is currently in muted mode.