player: fix demuxer lifetime management

Commit f54220d9 attempted to improve this, but it got worse. Now there
was a crash when ytdl_hook.lua added external tracks. This happened
because close_unused_demuxers() assumed that sources[0] was the main
demuxer (so that it didn't close it). This assumption failed, because
the ytdl script can add external tracks before the main file is loaded.
The easy fix would have been to check for master_demuxer, and not i==0.
But instead give up on the old idea, make some stricter assumptions how
demuxers and external tracks map, and simplify the code.

player/core.h

@@ -180,7 +180,7 @@ typedef struct MPContext {
     int64_t shown_vframes, shown_aframes;
 
     struct stream *stream; // stream that was initially opened
-    struct demuxer **sources;
+    struct demuxer **sources; // all open demuxers
     int num_sources;
 
     struct timeline *tl;
@@ -191,7 +191,7 @@ typedef struct MPContext {
     int num_chapters;
     double video_offset;
 
-    struct demuxer *demuxer;
+    struct demuxer *demuxer; // can change with timeline
     struct mp_tags *filtered_tags;
 
     struct track **tracks;

player/loadfile.c

@@ -59,66 +59,45 @@
 #include "command.h"
 #include "libmpv/client.h"
 
-static void close_unused_demuxers(struct MPContext *mpctx)
-{
-    for (int i = mpctx->num_sources - 1; i >= 0; i--) {
-        struct demuxer *d = mpctx->sources[i];
-
-        if (i == 0 || d == mpctx->track_layout)
-            goto skip;
-        for (int t = 0; t < mpctx->num_tracks; t++) {
-            if (d == mpctx->tracks[t]->demuxer)
-                goto skip;
-        }
-        for (int t = 0; t < mpctx->num_timeline_parts; t++) {
-            if (mpctx->timeline[t].source == d)
-                goto skip;
-        }
-
-        uninit_stream_sub_decoders(d);
-        free_demuxer_and_stream(d);
-        MP_TARRAY_REMOVE_AT(mpctx->sources, mpctx->num_sources, i);
-
-    skip:;
-    }
-}
-
 static void uninit_demuxer(struct MPContext *mpctx)
 {
     assert(!mpctx->d_video && !mpctx->d_audio &&
            !mpctx->d_sub[0] && !mpctx->d_sub[1]);
-    for (int i = 0; i < mpctx->num_tracks; i++) {
-        talloc_free(mpctx->tracks[i]);
-    }
-    mpctx->num_tracks = 0;
     for (int r = 0; r < NUM_PTRACKS; r++) {
         for (int t = 0; t < STREAM_TYPE_COUNT; t++)
             mpctx->current_track[r][t] = NULL;
     }
     mpctx->track_layout = NULL;
-    mpctx->master_demuxer = NULL;
     mpctx->demuxer = NULL;
-    if (!mpctx->tl)
-        mpctx->num_timeline_parts = 0;
-    for (int i = 0; i < mpctx->num_sources; i++)
-        uninit_stream_sub_decoders(mpctx->sources[i]);
-    close_unused_demuxers(mpctx);
-    if (mpctx->tl) {
-        timeline_destroy(mpctx->tl);
-    } else {
-        talloc_free(mpctx->timeline);
-    }
-    mpctx->timeline = NULL;
-    mpctx->num_timeline_parts = 0;
-    mpctx->tl = NULL;
-    if (mpctx->num_sources > 0)
-        free_demuxer(mpctx->sources[0]);
-    talloc_free(mpctx->sources);
-    mpctx->sources = NULL;
-    mpctx->num_sources = 0;
     talloc_free(mpctx->chapters);
     mpctx->chapters = NULL;
     mpctx->num_chapters = 0;
+
+    // per-stream cached subtitle state
+    for (int i = 0; i < mpctx->num_sources; i++)
+        uninit_stream_sub_decoders(mpctx->sources[i]);
+
+    // close demuxers for external tracks
+    for (int n = mpctx->num_tracks - 1; n >= 0; n--) {
+        mpctx->tracks[n]->selected = false;
+        mp_remove_track(mpctx, mpctx->tracks[n]);
+    }
+    for (int i = 0; i < mpctx->num_tracks; i++)
+        talloc_free(mpctx->tracks[i]);
+    mpctx->num_tracks = 0;
+
+    mpctx->timeline = NULL;
+    mpctx->num_timeline_parts = 0;
+    timeline_destroy(mpctx->tl);
+    mpctx->tl = NULL;
+
+    free_demuxer(mpctx->master_demuxer);
+    mpctx->master_demuxer = NULL;
+
+    talloc_free(mpctx->sources);
+    mpctx->sources = NULL;
+    mpctx->num_sources = 0;
+
     mpctx->video_offset = 0;
 }
 
@@ -660,13 +639,23 @@ bool mp_remove_track(struct MPContext *mpctx, struct track *track)
     if (track->selected)
         return false;
 
+    struct demuxer *d = track->demuxer;
+
     int index = 0;
     while (index < mpctx->num_tracks && mpctx->tracks[index] != track)
         index++;
     MP_TARRAY_REMOVE_AT(mpctx->tracks, mpctx->num_tracks, index);
     talloc_free(track);
 
-    close_unused_demuxers(mpctx);
+    // Close the demuxer, unless there is still a track using it. These are
+    // all external tracks, so there are no complications due to the timeline
+    // mechanism switching the track's demuxer dynamically.
+    bool in_use = false;
+    for (int n = mpctx->num_tracks - 1; n >= 0 && !in_use; n--)
+        in_use |= mpctx->tracks[n]->demuxer == d;
+
+    if (!in_use)
+        free_demuxer_and_stream(d);
 
     mp_notify(mpctx, MPV_EVENT_TRACKS_CHANGED, NULL);
 
@@ -975,7 +964,7 @@ static void open_demux_reentrant(struct MPContext *mpctx)
     mpctx_run_reentrant(mpctx, open_demux_thread, &args);
     if (args.demux) {
         talloc_steal(args.demux, args.global);
-        mpctx->demuxer = args.demux;
+        mpctx->master_demuxer = args.demux;
         mpctx->tl = args.tl;
     } else {
         talloc_free(args.global);
@@ -984,9 +973,10 @@ static void open_demux_reentrant(struct MPContext *mpctx)
 
 static void load_timeline(struct MPContext *mpctx)
 {
-    mpctx->track_layout = mpctx->demuxer;
+    mpctx->track_layout = mpctx->master_demuxer;
 
-    MP_TARRAY_APPEND(NULL, mpctx->sources, mpctx->num_sources, mpctx->demuxer);
+    MP_TARRAY_APPEND(NULL, mpctx->sources, mpctx->num_sources,
+                     mpctx->master_demuxer);
 
     if (mpctx->tl) {
         mpctx->timeline = mpctx->tl->parts;
@@ -995,10 +985,11 @@ static void load_timeline(struct MPContext *mpctx)
         mpctx->chapters = demux_copy_chapter_data(mpctx->tl->chapters,
                                                   mpctx->tl->num_chapters);
         mpctx->track_layout = mpctx->tl->track_layout;
-        mpctx->num_sources = 0;
         for (int n = 0; n < mpctx->tl->num_sources; n++) {
-            MP_TARRAY_APPEND(NULL, mpctx->sources, mpctx->num_sources,
-                             mpctx->tl->sources[n]);
+            if (mpctx->tl->sources[n] != mpctx->master_demuxer) {
+                MP_TARRAY_APPEND(NULL, mpctx->sources, mpctx->num_sources,
+                                 mpctx->tl->sources[n]);
+            }
         }
     }
 
@@ -1111,12 +1102,12 @@ goto_reopen_demuxer: ;
     mp_nav_reset(mpctx);
 
     open_demux_reentrant(mpctx);
-    if (!mpctx->demuxer) {
+    if (!mpctx->master_demuxer) {
         MP_ERR(mpctx, "Failed to recognize file format.\n");
         mpctx->error_playing = MPV_ERROR_UNKNOWN_FORMAT;
         goto terminate_playback;
     }
-    mpctx->master_demuxer = mpctx->demuxer;
+    mpctx->demuxer = mpctx->master_demuxer;
 
     load_timeline(mpctx);