From b9250569cdae1d31b728cfd8f5d7f7c8f41090d3 Mon Sep 17 00:00:00 2001
From: wm4 <wm4@nowhere>
Date: Mon, 3 Jun 2019 02:15:19 +0200
Subject: demux: fix assertion when switching tracks during backward playback

Someone who rams a knife into his own hand just to see what happens is
normally put in a psychiatric ward. But in software, this is acceptable
behavior. Programs are not supposed to crash just because a user did
something unreasonably dumb.

Switching tracks during backward playback is such a thing. It triggered
an assertion because the newly enabled stream was not properly
initialized for backward playback. Fix this, and make it actually work
(mostly; it still takes a "while" until playback recovers fully).

This actually makes some aspects of initialization slightly cleaner.
---
 demux/demux.c | 40 ++++++++++++++++++++--------------------
 1 file changed, 20 insertions(+), 20 deletions(-)

(limited to 'demux')

diff --git a/demux/demux.c b/demux/demux.c
index 3f65b2f158..b3048aacdd 100644
--- a/demux/demux.c
+++ b/demux/demux.c
@@ -787,8 +787,8 @@ static void ds_clear_reader_state(struct demux_stream *ds,
         ds->back_restart_pos = -1;
         ds->back_restart_dts = MP_NOPTS_VALUE;
         ds->back_restart_eof = false;
-        ds->back_restart_next = false;
-        ds->back_restarting = false;
+        ds->back_restart_next = ds->in->back_demuxing;
+        ds->back_restarting = ds->in->back_demuxing && ds->eager;
         ds->back_seek_pos = MP_NOPTS_VALUE;
         ds->back_resume_pos = -1;
         ds->back_resume_dts = MP_NOPTS_VALUE;
@@ -821,8 +821,6 @@ static void update_stream_selection_state(struct demux_internal *in,
     ds->eof = false;
     ds->refreshing = false;
 
-    ds_clear_reader_state(ds, true);
-
     // We still have to go over the whole stream list to update ds->eager for
     // other streams too, because they depend on other stream's selections.
 
@@ -862,6 +860,8 @@ static void update_stream_selection_state(struct demux_internal *in,
     if (!any_streams)
         in->blocked = false;
 
+    ds_clear_reader_state(ds, true);
+
     // Make sure any stream reselection or addition is reflected in the seek
     // ranges, and also get rid of data that is not needed anymore (or
     // rather, which can't be kept consistent). This has to happen after we've
@@ -1511,8 +1511,10 @@ resume_earlier:
         }
     }
 
-    ds->back_seek_pos -= in->opts->back_seek_size;
-    in->need_back_seek = true;
+    if (ds->back_seek_pos != MP_NOPTS_VALUE) {
+        ds->back_seek_pos -= in->opts->back_seek_size;
+        in->need_back_seek = true;
+    }
 }
 
 // Process that one or multiple packets were added.
@@ -3347,14 +3349,14 @@ static bool queue_seek(struct demux_internal *in, double seek_pts, int flags,
         }
     }
 
-    clear_reader_state(in, clear_back_state);
-
     in->eof = false;
     in->last_eof = false;
     in->idle = true;
     in->reading = false;
     in->back_demuxing = set_backwards;
 
+    clear_reader_state(in, clear_back_state);
+
     if (cache_target) {
         execute_cache_seek(in, cache_target, seek_pts, flags);
     } else {
@@ -3368,22 +3370,15 @@ static bool queue_seek(struct demux_internal *in, double seek_pts, int flags,
     for (int n = 0; n < in->num_streams; n++) {
         struct demux_stream *ds = in->streams[n]->ds;
 
-        if (in->back_demuxing && clear_back_state) {
+        // Process possibly cached packets.
+        if (in->back_demuxing) {
             ds->back_seek_pos = seek_pts;
-            ds->back_restarting = ds->eager;
-            ds->back_restart_next = true;
+            back_demux_see_packets(in->streams[n]->ds);
         }
 
         wakeup_ds(ds);
     }
 
-    if (in->back_demuxing) {
-        // Process possibly cached packets. Separate from the loop above, since
-        // all flags must be set on all streams before this function is called.
-        for (int n = 0; n < in->num_streams; n++)
-            back_demux_see_packets(in->streams[n]->ds);
-    }
-
     if (!in->threading && in->seeking)
         execute_seek(in);
 
@@ -3488,14 +3483,19 @@ void demuxer_select_track(struct demuxer *demuxer, struct sh_stream *stream,
     struct demux_internal *in = demuxer->in;
     struct demux_stream *ds = stream->ds;
     pthread_mutex_lock(&in->lock);
+    ref_pts = MP_ADD_PTS(ref_pts, -in->ts_offset);
     // don't flush buffers if stream is already selected / unselected
     if (ds->selected != selected) {
         MP_VERBOSE(in, "%sselect track %d\n", selected ? "" : "de", stream->index);
         ds->selected = selected;
         update_stream_selection_state(in, ds);
         in->tracks_switched = true;
-        if (ds->selected && !in->after_seek)
-            initiate_refresh_seek(in, ds, MP_ADD_PTS(ref_pts, -in->ts_offset));
+        if (ds->selected) {
+            if (in->back_demuxing)
+                ds->back_seek_pos = ref_pts;
+            if (!in->after_seek)
+                initiate_refresh_seek(in, ds, ref_pts);
+        }
         if (in->threading) {
             pthread_cond_signal(&in->wakeup);
         } else {
-- 
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