Fix ordered chapter pruning of redundant timeline parts

Code that was supposed to merge two timeline parts if the second one
started exactly where the first one stopped didn't work because it
mixed timestamps in different units (I had changed the units of some
variables after originally writing that code but forgotten to update
it). As a result of the bug there were unnecessary part switches, but
it was unlikely to cause any serious problems.

1 files changed, 8 insertions, 5 deletions

diff --git a/mplayer.c b/mplayer.c
index 259407d027..a09333f662 100644
--- a/mplayer.c
+++ b/mplayer.c
@@ -2782,6 +2782,7 @@ static void build_ordered_chapter_timeline(struct MPContext *mpctx)
     uint64_t missing_time = 0;
     int part_count = 0;
     int num_chapters = 0;
+    uint64_t prev_part_offset;
     for (int i = 0; i < m->num_ordered_chapters; i++) {
         struct matroska_chapter *c = m->ordered_chapters + i;
 
@@ -2795,15 +2796,17 @@ static void build_ordered_chapter_timeline(struct MPContext *mpctx)
     found2:;
         chapters[num_chapters].start = starttime / 1000.;
         chapters[num_chapters].name = talloc_strdup(chapters, c->name);
-        // Only add a separate part if the time or file actually changes
-        uint64_t prev_end = !part_count ? 0 : starttime
-            - timeline[part_count - 1].start
-            + timeline[part_count - 1].source_start;
-        if (part_count == 0 || c->start != prev_end
+        /* Only add a separate part if the time or file actually changes.
+         * Matroska files have chapter divisions that are redundant from
+         * timeline point of view because the same chapter structure is used
+         * both to specify the timeline and for normal chapter information.
+         * Removing a missing inserted external chapter can also cause this. */
+        if (part_count == 0 || c->start != starttime + prev_part_offset
             || sources + j != timeline[part_count - 1].source) {
             timeline[part_count].source = sources + j;
             timeline[part_count].start = chapters[num_chapters].start;
             timeline[part_count].source_start = c->start / 1000.;
+            prev_part_offset = c->start - starttime;
             part_count++;
         }
         starttime += c->end - c->start;