demux_mkv: adjust subtitle preroll again (2)

Make the changes started in commit c827ae5f more eloborate, and provide
an option to control the amount of data read before the seek-target. To
achieve this, rewrite the loop that finds the lowest still acceptable
target cluster. It is now searched by time instead of file position. The
behavior (both with and without preroll option) may be different from
before this change, although it shouldn't be worse.

The change demux_mkv_read_cues() fixes a bug: when seeking after playing
normally, the code would erroneously assume that durations are set. This
doesn't happen if the first operation after loading was a seek instead
of playback.

2 files changed, 4 insertions, 0 deletions

diff --git a/options/options.c b/options/options.c
index c15482fd05..ba251f6216 100644
--- a/options/options.c
+++ b/options/options.c
@@ -301,6 +301,8 @@ const m_option_t mp_opts[] = {
 
     OPT_FLAG("demuxer-mkv-subtitle-preroll", mkv_subtitle_preroll, 0),
     OPT_FLAG("mkv-subtitle-preroll", mkv_subtitle_preroll, 0), // old alias
+    OPT_DOUBLE("demuxer-mkv-subtitle-preroll-secs", mkv_subtitle_preroll_secs,
+               M_OPT_MIN, .min = 0),
 
 // ------------------------- subtitles options --------------------
 
@@ -670,6 +672,7 @@ const struct MPOpts mp_default_opts = {
     .use_embedded_fonts = 1,
     .sub_fix_timing = 1,
     .sub_cp = "auto",
+    .mkv_subtitle_preroll_secs = 1.0,
 
     .hwdec_codecs = "h264,vc1,wmv3",
 
diff --git a/options/options.h b/options/options.h
index f67a3a5c95..9284320f40 100644
--- a/options/options.h
+++ b/options/options.h
@@ -194,6 +194,7 @@ typedef struct MPOpts {
     char *audio_demuxer_name;
     char *sub_demuxer_name;
     int mkv_subtitle_preroll;
+    double mkv_subtitle_preroll_secs;
 
     double demuxer_min_secs_cache;
     int cache_pausing;