core: ordered chapters: add heuristic for merging inaccurate chapters

Some Matroska files have inaccurate ordered chapter endpoints, and so
parts where one chapter should end and the next begin at the same
timestamp were not merged. This resulted in an unnecessary seek over a
minimal distance. Add a heuristic to merge parts with a minimal gap or
overlap between them.

Based on patch by Hector Martin <hector@marcansoft.com>.

1 files changed, 18 insertions, 6 deletions

diff --git a/mplayer.c b/mplayer.c
index 8821b3df89..4707936447 100644
--- a/mplayer.c
+++ b/mplayer.c
@@ -3100,7 +3100,9 @@ static int find_ordered_chapter_sources(struct MPContext *mpctx,
 
 static void build_ordered_chapter_timeline(struct MPContext *mpctx)
 {
-    if (!mpctx->opts.ordered_chapters) {
+    struct MPOpts *opts = &mpctx->opts;
+
+    if (!opts->ordered_chapters) {
         mp_msg(MSGT_CPLAYER, MSGL_INFO, "File uses ordered chapters, but "
                "you have disabled support for them. Ignoring.\n");
         return;
@@ -3162,21 +3164,31 @@ static void build_ordered_chapter_timeline(struct MPContext *mpctx)
         missing_time += c->end - c->start;
         continue;
     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.
          * 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
+         * Removing a missing inserted external chapter can also cause this.
+         * We allow for a configurable fudge factor because of files which
+         * specify chapter end times that are one frame too early;
+         * we don't want to try seeking over a one frame gap. */
+        int64_t join_diff = c->start - starttime - prev_part_offset;
+        if (part_count == 0 || FFABS(join_diff) > opts->chapter_merge_threshold
             || sources + j != timeline[part_count - 1].source) {
             timeline[part_count].source = sources + j;
-            timeline[part_count].start = chapters[num_chapters].start;
+            timeline[part_count].start = starttime / 1000.;
             timeline[part_count].source_start = c->start / 1000.;
             prev_part_offset = c->start - starttime;
             part_count++;
+        } else if (part_count > 0 && join_diff) {
+            /* Chapter was merged at an inexact boundary;
+             * adjust timestamps to match. */
+            mp_msg(MSGT_CPLAYER, MSGL_V, "Merging timeline part %d with "
+                   "offset %d ms.\n", i, (int) join_diff);
+            starttime += join_diff;
         }
+        chapters[num_chapters].start = starttime / 1000.;
+        chapters[num_chapters].name = talloc_strdup(chapters, c->name);
         starttime += c->end - c->start;
         num_chapters++;
     }