core: fix backstepping with ordered chapters

There were two problems.

First, frames past the end of the current segment were added to the
index, which messed up backstepping. Check for the endpts before
added a frame to the index.

Second, it wasn't possible to step over segments which change the file.
Changing a file causes decoder reinitialization, which (rightfully)
is treated as discontinuity (and vo_pts_history_seek_ts was changed).
Add some extra code to pretend that a segment-switching seek/reinit
does not introduce discontinuities.

There's still a weird corner case: sometimes, you can frame step forward
on the last frame of a segment without reaching the next segment
immediately. This is because the playloop switches into audio-only mode.
The segment is switched when both audio and video have ended, so the
frame stepping will play random sized chunks of audio until the segment
will be switched. This gives the impression that backstepping doesn't
work perfectly, even though it's the other way around and frame stepping
behaves weird. This is a consequence of wanting to make frame stepping
work with audio, and is not really a bug.

1 files changed, 13 insertions, 5 deletions

diff --git a/core/mplayer.c b/core/mplayer.c
index 08a3d8256d..36d0d59998 100644
--- a/core/mplayer.c
+++ b/core/mplayer.c
@@ -2549,7 +2549,7 @@ static void determine_frame_pts(struct MPContext *mpctx)
                     sh_video->codec_reordered_pts : sh_video->sorted_pts;
 }
 
-static double update_video(struct MPContext *mpctx)
+static double update_video(struct MPContext *mpctx, double endpts)
 {
     struct sh_video *sh_video = mpctx->sh_video;
     struct vo *video_out = mpctx->video_out;
@@ -2606,7 +2606,8 @@ static double update_video(struct MPContext *mpctx)
         if (pts == MP_NOPTS_VALUE)
             pts = sh_video->last_pts;
     }
-    add_frame_pts(mpctx, pts);
+    if (endpts != MP_NOPTS_VALUE && pts < endpts)
+        add_frame_pts(mpctx, pts);
     if (mpctx->hrseek_active && pts < mpctx->hrseek_pts - .005) {
         vo_skip_frame(video_out);
         return 0;
@@ -2745,8 +2746,6 @@ static void seek_reset(struct MPContext *mpctx, bool reset_ao, bool reset_ac)
     mpctx->drop_frame_cnt = 0;
     mpctx->dropped_frames = 0;
     mpctx->playback_pts = MP_NOPTS_VALUE;
-    mpctx->vo_pts_history_seek_ts++;
-    mpctx->backstep_active = false;
 
 #ifdef CONFIG_ENCODING
     encode_lavc_discontinuity(mpctx->encode_lavc_ctx);
@@ -2809,6 +2808,7 @@ static int seek(MPContext *mpctx, struct seek_params seek,
                 bool timeline_fallthrough)
 {
     struct MPOpts *opts = &mpctx->opts;
+    uint64_t prev_seek_ts = mpctx->vo_pts_history_seek_ts;
 
     if (!mpctx->demuxer)
         return -1;
@@ -2915,6 +2915,14 @@ static int seek(MPContext *mpctx, struct seek_params seek,
      * and resetting could lose audio some decoders produce during init. */
     seek_reset(mpctx, !timeline_fallthrough, !need_reset);
 
+    if (timeline_fallthrough) {
+        // Important if video reinit happens.
+        mpctx->vo_pts_history_seek_ts = prev_seek_ts;
+    } else {
+        mpctx->vo_pts_history_seek_ts++;
+        mpctx->backstep_active = false;
+    }
+
     /* Use the target time as "current position" for further relative
      * seeks etc until a new video frame has been decoded */
     if (seek.type == MPSEEK_ABSOLUTE) {
@@ -3266,7 +3274,7 @@ static void run_playloop(struct MPContext *mpctx)
 
         video_left = vo->hasframe || vo->frame_loaded;
         if (!vo->frame_loaded && (!mpctx->paused || mpctx->restart_playback)) {
-            double frame_time = update_video(mpctx);
+            double frame_time = update_video(mpctx, endpts);
             mp_dbg(MSGT_AVSYNC, MSGL_DBG2, "*** ftime=%5.3f ***\n", frame_time);
             if (mpctx->sh_video->vf_initialized < 0) {
                 mp_tmsg(MSGT_CPLAYER, MSGL_FATAL,