demux_mkv: adjust subtitle preroll defaults

Always preroll by default if the cue (index) information indicates
overlapping subtitles.

Increase the amount of maximum data it will skip to get such subtitles
to 10 seconds. Since the index information can reliably tell whether
reading earlier is needed, the maximum should be rarely actually used,
thus we can set it high. On the other hand, the "old" prerolling
mechanism always has to skip the maximum amount of data; thus the method
using the index gets its own option to control the maximum amount of
data to skip.

(As more and more files With newer mkvtoolnix versions are muxed, and
with this new and hopefully sane default established, these options can
probably be removed in the future.)

1 files changed, 13 insertions, 3 deletions

diff --git a/demux/demux_mkv.c b/demux/demux_mkv.c
index af82dc8deb..4b4e16c4b6 100644
--- a/demux/demux_mkv.c
+++ b/demux/demux_mkv.c
@@ -202,15 +202,19 @@ typedef struct mkv_demuxer {
 struct demux_mkv_opts {
     int subtitle_preroll;
     double subtitle_preroll_secs;
+    double subtitle_preroll_secs_index;
     int probe_duration;
     int probe_start_time;
 };
 
 const struct m_sub_options demux_mkv_conf = {
     .opts = (const m_option_t[]) {
-        OPT_FLAG("subtitle-preroll", subtitle_preroll, 0),
+        OPT_CHOICE("subtitle-preroll", subtitle_preroll, 0,
+                   ({"no", 0}, {"yes", 1}, {"index", 2})),
         OPT_DOUBLE("subtitle-preroll-secs", subtitle_preroll_secs,
                    M_OPT_MIN, .min = 0),
+        OPT_DOUBLE("subtitle-preroll-secs-index", subtitle_preroll_secs_index,
+                   M_OPT_MIN, .min = 0),
         OPT_CHOICE("probe-video-duration", probe_duration, 0,
                    ({"no", 0}, {"yes", 1}, {"full", 2})),
         OPT_FLAG("probe-start-time", probe_start_time, 0),
@@ -218,7 +222,9 @@ const struct m_sub_options demux_mkv_conf = {
     },
     .size = sizeof(struct demux_mkv_opts),
     .defaults = &(const struct demux_mkv_opts){
+        .subtitle_preroll = 2,
         .subtitle_preroll_secs = 1.0,
+        .subtitle_preroll_secs_index = 10.0,
         .probe_start_time = 1,
     },
 };
@@ -2724,6 +2730,8 @@ static struct mkv_index *seek_with_cues(struct demuxer *demuxer, int seek_id,
             // Find the cluster with the highest filepos, that has a timestamp
             // still lower than min_tc.
             double secs = opts->demux_mkv->subtitle_preroll_secs;
+            if (mkv_d->index_has_durations)
+                secs = MPMAX(secs, opts->demux_mkv->subtitle_preroll_secs_index);
             uint64_t pre = MPMIN(INT64_MAX, secs * 1e9 / mkv_d->tc_scale);
             uint64_t min_tc = pre < index->timecode ? index->timecode - pre : 0;
             uint64_t prev_target = 0;
@@ -2786,8 +2794,10 @@ static void demux_mkv_seek(demuxer_t *demuxer, double rel_seek_secs, int flags)
     int cueflags = (flags & SEEK_BACKWARD) ? FLAG_BACKWARD : 0;
 
     mkv_d->subtitle_preroll = NUM_SUB_PREROLL_PACKETS;
-    if (((flags & SEEK_HR) || demuxer->opts->demux_mkv->subtitle_preroll) &&
-        st_active[STREAM_SUB] && st_active[STREAM_VIDEO])
+    int preroll_opt = demuxer->opts->demux_mkv->subtitle_preroll;
+    if (((flags & SEEK_HR) || preroll_opt == 1 ||
+         (preroll_opt == 2 && mkv_d->index_has_durations))
+        && st_active[STREAM_SUB] && st_active[STREAM_VIDEO])
         cueflags |= FLAG_SUBPREROLL;
 
     // Adjust the target a little bit to catch cases where the target position