core: add demux_sub pseudo demuxer

Subtitle files are opened in mplayer.c, not using the demuxer
infrastructure in general. Pretend that this is not the case (outside of
the loading code) by opening a pseudo demuxer that does nothing. One
advantage is that the initialization code is now the same, and there's
no confusion about what the difference between track->stream,
track->sh_sub and mpctx->sh_sub is supposed to be.

This is a bit stupid, and it would be much better if there were proper
subtitle demuxers (there are many in recent FFmpeg, but not Libav). So
for now this is just a transition to a more proper architecture. Look
at demux_sub like an artifical limb: it's ugly, but don't hate it - it
helps you to get on with your life.

9 files changed, 108 insertions, 77 deletions

diff --git a/Makefile b/Makefile
index e91564703e..6e52253543 100644
--- a/Makefile
+++ b/Makefile
@@ -205,6 +205,7 @@ SOURCES = talloc.c \
           demux/demux_mf.c \
           demux/demux_mkv.c \
           demux/demux_mpg.c \
+          demux/demux_sub.c \
           demux/demux_ts.c \
           demux/mp3_hdr.c \
           demux/parse_es.c \
diff --git a/core/mp_core.h b/core/mp_core.h
index db6bc570e1..d7aa42e38d 100644
--- a/core/mp_core.h
+++ b/core/mp_core.h
@@ -103,12 +103,9 @@ struct track {
     // Invariant: (!demuxer && !stream) || stream->demuxer == demuxer
     struct sh_stream *stream;
 
-    // NOTE: demuxer subtitles, i.e. if stream!=NULL, do not use the following
-    //       fields. The data is stored in stream->sub this case.
-
-    // External text subtitle using libass subtitle renderer.
-    // The sh_sub is a dummy and doesn't belong to a demuxer.
-    struct sh_sub *sh_sub;
+    // For external subtitles, which are read fully on init. Do not attempt
+    // to read packets from them.
+    bool preloaded;
 };
 
 enum {
diff --git a/core/mplayer.c b/core/mplayer.c
index 285f19c8ac..a19788df0b 100644
--- a/core/mplayer.c
+++ b/core/mplayer.c
@@ -281,8 +281,6 @@ static void print_stream(struct MPContext *mpctx, struct track *t)
     if (t->title)
         mp_msg(MSGT_CPLAYER, MSGL_INFO, " '%s'", t->title);
     const char *codec = s ? s->codec : NULL;
-    if (!codec && t->sh_sub) // external subs hack
-        codec = t->sh_sub->gsh->codec;
     mp_msg(MSGT_CPLAYER, MSGL_INFO, " (%s)", codec ? codec : "<unknown>");
     if (t->is_external)
         mp_msg(MSGT_CPLAYER, MSGL_INFO, " (external)");
@@ -482,13 +480,8 @@ void uninit_player(struct MPContext *mpctx, unsigned int mask)
 
     if (mask & INITIALIZED_SUB) {
         mpctx->initialized_flags &= ~INITIALIZED_SUB;
-        struct track *track = mpctx->current_track[STREAM_SUB];
-        // One of these was active; they can't be both active.
-        assert(!(mpctx->sh_sub && track && track->sh_sub));
         if (mpctx->sh_sub)
             sub_switchoff(mpctx->sh_sub, mpctx->osd);
-        if (track && track->sh_sub)
-            sub_switchoff(track->sh_sub, mpctx->osd);
         cleanup_demux_stream(mpctx, STREAM_SUB);
         reset_subtitles(mpctx);
     }
@@ -1039,11 +1032,19 @@ static void add_dvd_tracks(struct MPContext *mpctx)
 #endif
 }
 
+#ifdef CONFIG_ASS
+static int free_ass_track(void *ptr)
+{
+    struct ass_track *track = *(struct ass_track **)ptr;
+    ass_free_track(track);
+    return 1;
+}
+#endif
+
 struct track *mp_add_subtitles(struct MPContext *mpctx, char *filename,
                                float fps, int noerr)
 {
     struct MPOpts *opts = &mpctx->opts;
-    struct sh_sub *sh = NULL;
     struct ass_track *asst = NULL;
     const char *codec = NULL;
 
@@ -1067,33 +1068,37 @@ struct track *mp_add_subtitles(struct MPContext *mpctx, char *filename,
         }
         talloc_free(subd);
     }
-    if (asst)
-        sh = sd_ass_create_from_track(asst, codec, opts);
-#endif
+    if (asst) {
+        struct demuxer *d = new_sub_pseudo_demuxer(opts);
+        assert(d->num_streams == 1);
+        struct sh_stream *s = d->streams[0];
+        assert(s->type == STREAM_SUB);
 
-    if (!sh) {
-        // Used with image subtitles.
-        struct track *ext = open_external_file(mpctx, filename, NULL, 0,
-                                               STREAM_SUB);
-        if (ext)
-            return ext;
-        mp_tmsg(MSGT_CPLAYER, noerr ? MSGL_WARN : MSGL_ERR,
-                "Cannot load subtitles: %s\n", filename);
-        return NULL;
+        s->sub->track = asst;
+        s->codec = codec;
+
+        struct ass_track **pptr = talloc(s, struct ass_track*);
+        *pptr = asst;
+        talloc_set_destructor(pptr, free_ass_track);
+
+        struct track *t = add_stream_track(mpctx, s, false);
+        t->is_external = true;
+        t->preloaded = true;
+        t->title = talloc_strdup(t, filename);
+        t->external_filename = talloc_strdup(t, filename);
+        MP_TARRAY_APPEND(NULL, mpctx->sources, mpctx->num_sources, d);
+        return t;
     }
+#endif
 
-    struct track *track = talloc_ptrtype(NULL, track);
-    *track = (struct track) {
-        .type = STREAM_SUB,
-        .title = talloc_strdup(track, filename),
-        .user_tid = find_new_tid(mpctx, STREAM_SUB),
-        .demuxer_id = -1,
-        .is_external = true,
-        .sh_sub = talloc_steal(track, sh),
-        .external_filename = talloc_strdup(track, filename),
-    };
-    MP_TARRAY_APPEND(mpctx, mpctx->tracks, mpctx->num_tracks, track);
-    return track;
+    // Used with libavformat subtitles.
+    struct track *ext = open_external_file(mpctx, filename, NULL, 0, STREAM_SUB);
+    if (ext)
+        return ext;
+
+    mp_tmsg(MSGT_CPLAYER, noerr ? MSGL_WARN : MSGL_ERR,
+            "Cannot load subtitles: %s\n", filename);
+    return NULL;
 }
 
 int mp_get_cache_percent(struct MPContext *mpctx)
@@ -1845,7 +1850,7 @@ static void update_subtitles(struct MPContext *mpctx, double refpts_tl)
     double curpts_s = refpts_tl - mpctx->osd->sub_offset;
     double refpts_s = refpts_tl - video_offset;
 
-    if (sh_sub && sh_sub->active) {
+    if (sh_sub && sh_sub->active && !track->preloaded) {
         struct demux_stream *d_sub = sh_sub->ds;
         const char *type = sh_sub->gsh->codec;
         bool non_interleaved = is_non_interleaved(mpctx, track);
@@ -2017,9 +2022,7 @@ static void reinit_subs(struct MPContext *mpctx)
     osd->sub_video_w = mpctx->sh_video ? mpctx->sh_video->disp_w : 0;
     osd->sub_video_h = mpctx->sh_video ? mpctx->sh_video->disp_h : 0;
 
-    if (track->sh_sub) {
-        sub_init(track->sh_sub, osd);
-    } else if (track->stream) {
+    if (track->stream) {
         if (track->demuxer && track->demuxer->stream) {
             set_dvdsub_fake_extradata(mpctx->sh_sub, track->demuxer->stream,
                                       osd->sub_video_w, osd->sub_video_h);
diff --git a/demux/demux.c b/demux/demux.c
index 3e27b43f93..12e0d9083a 100644
--- a/demux/demux.c
+++ b/demux/demux.c
@@ -66,6 +66,7 @@ extern const demuxer_desc_t demuxer_desc_mpeg_es;
 extern const demuxer_desc_t demuxer_desc_mpeg4_es;
 extern const demuxer_desc_t demuxer_desc_h264_es;
 extern const demuxer_desc_t demuxer_desc_mpeg_ts;
+extern const demuxer_desc_t demuxer_desc_sub;
 
 /* Please do not add any new demuxers here. If you want to implement a new
  * demuxer, add it to libavformat, except for wrappers around external
@@ -95,6 +96,8 @@ const demuxer_desc_t *const demuxer_list[] = {
     &demuxer_desc_mpeg_ts,
     // auto-probe last, because it checks file-extensions only
     &demuxer_desc_mf,
+    // no auto-probe
+    &demuxer_desc_sub,
     /* Please do not add any new demuxers here. If you want to implement a new
      * demuxer, add it to libavformat, except for wrappers around external
      * libraries and demuxers requiring binary support. */
@@ -217,8 +220,8 @@ static const demuxer_desc_t *get_demuxer_desc_from_type(int file_format)
 }
 
 
-demuxer_t *new_demuxer(struct MPOpts *opts, stream_t *stream, int type,
-                       int a_id, int v_id, int s_id, char *filename)
+static demuxer_t *new_demuxer(struct MPOpts *opts, stream_t *stream, int type,
+                              int a_id, int v_id, int s_id, char *filename)
 {
     struct demuxer *d = talloc_zero(NULL, struct demuxer);
     d->stream = stream;
@@ -248,6 +251,18 @@ demuxer_t *new_demuxer(struct MPOpts *opts, stream_t *stream, int type,
     return d;
 }
 
+// for demux_sub.c
+demuxer_t *new_sub_pseudo_demuxer(struct MPOpts *opts)
+{
+    struct stream *s = open_stream("null://", NULL, NULL);
+    assert(s);
+    struct demuxer *d = new_demuxer(opts, s, DEMUXER_TYPE_SUB,
+                                    -1, -1, -1, NULL);
+    new_sh_stream(d, STREAM_SUB);
+    talloc_steal(d, s);
+    return d;
+}
+
 static struct sh_stream *new_sh_stream_id(demuxer_t *demuxer,
                                           enum stream_type type,
                                           int stream_index,
diff --git a/demux/demux.h b/demux/demux.h
index 886252fa85..e58c56141f 100644
--- a/demux/demux.h
+++ b/demux/demux.h
@@ -77,6 +77,7 @@ enum demuxer_type {
     DEMUXER_TYPE_END,
 
     DEMUXER_TYPE_PLAYLIST,
+    DEMUXER_TYPE_SUB,
 };
 
 enum timestamp_type {
@@ -304,9 +305,9 @@ static inline void *realloc_struct(void *ptr, size_t nmemb, size_t size)
     return realloc(ptr, nmemb * size);
 }
 
-struct demuxer *new_demuxer(struct MPOpts *opts, struct stream *stream,
-                            int type, int a_id, int v_id, int s_id,
-                            char *filename);
+demuxer_t *new_sub_pseudo_demuxer(struct MPOpts *opts);
+
+
 void free_demuxer(struct demuxer *demuxer);
 
 void demuxer_add_packet(demuxer_t *demuxer, struct sh_stream *stream,
diff --git a/demux/demux_sub.c b/demux/demux_sub.c
new file mode 100644
index 0000000000..ab99091215
--- /dev/null
+++ b/demux/demux_sub.c
@@ -0,0 +1,38 @@
+/*
+ * This file is part of mpv.
+ *
+ * mpv is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation; either version 2 of the License, or
+ * (at your option) any later version.
+ *
+ * mpv is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License along
+ * with mpv.  If not, see <http://www.gnu.org/licenses/>.
+ */
+
+// Note: not a real demuxer. The frontend has its own code to open subtitle
+//       code, and then creates a new dummy demuxer with new_sub_demuxer().
+//       But eventually, all subtitles should be opened this way, and this
+//       file can be removed.
+
+#include "demux.h"
+
+static int dummy_fill_buffer(struct demuxer *demuxer, struct demux_stream *ds)
+{
+    return 0;
+}
+
+const struct demuxer_desc demuxer_desc_sub = {
+    .info = "External subtitles pseudo demuxer",
+    .name = "sub",
+    .shortdesc = "sub",
+    .author = "",
+    .comment = "",
+    .type = DEMUXER_TYPE_SUB,
+    .fill_buffer = dummy_fill_buffer,
+};
diff --git a/demux/stheader.h b/demux/stheader.h
index 433dc7ef71..09e9d8682b 100644
--- a/demux/stheader.h
+++ b/demux/stheader.h
@@ -164,6 +164,7 @@ typedef struct sh_sub {
     bool active; // after track switch decoder may stay initialized, not active
     unsigned char *extradata;   // extra header data passed from demuxer
     int extradata_len;
+    struct ass_track *track; // loaded by libass
     const struct sd_functions *sd_driver;
 } sh_sub_t;
 
diff --git a/sub/dec_sub.h b/sub/dec_sub.h
index 263df19bc0..4eb833c52b 100644
--- a/sub/dec_sub.h
+++ b/sub/dec_sub.h
@@ -21,9 +21,6 @@ void sub_reset(struct sh_sub *sh, struct osd_state *osd);
 void sub_switchoff(struct sh_sub *sh, struct osd_state *osd);
 void sub_uninit(struct sh_sub *sh);
 
-struct sh_sub *sd_ass_create_from_track(struct ass_track *track,
-                                        const char *codec, struct MPOpts *opts);
-
 #ifdef CONFIG_ASS
 struct ass_track *sub_get_ass_track(struct osd_state *osd);
 #endif
diff --git a/sub/sd_ass.c b/sub/sd_ass.c
index 02d0ed15bf..b107e0438f 100644
--- a/sub/sd_ass.c
+++ b/sub/sd_ass.c
@@ -79,7 +79,9 @@ static int init(struct sh_sub *sh, struct osd_state *osd)
     } else {
         ctx = talloc_zero(NULL, struct sd_ass_priv);
         sh->context = ctx;
-        if (ass) {
+        if (sh->track) {
+            ctx->ass_track = sh->track;
+        } else if (ass) {
             ctx->ass_track = ass_new_track(osd->ass_library);
             if (sh->extradata)
                 ass_process_codec_private(ctx->ass_track, sh->extradata,
@@ -277,7 +279,8 @@ static void uninit(struct sh_sub *sh)
 {
     struct sd_ass_priv *ctx = sh->context;
 
-    ass_free_track(ctx->ass_track);
+    if (sh->track != ctx->ass_track)
+        ass_free_track(ctx->ass_track);
     talloc_free(ctx);
 }
 
@@ -293,31 +296,6 @@ const struct sd_functions sd_ass = {
     .uninit = uninit,
 };
 
-static int sd_ass_track_destructor(void *ptr)
-{
-    uninit(ptr);
-    return 1;
-}
-
-struct sh_sub *sd_ass_create_from_track(struct ass_track *track,
-                                        const char *codec, struct MPOpts *opts)
-{
-    struct sh_sub *sh = talloc(NULL, struct sh_sub);
-    talloc_set_destructor(sh, sd_ass_track_destructor);
-    *sh = (struct sh_sub) {
-        .opts = opts,
-        .gsh = talloc_struct(sh, struct sh_stream, {
-            .codec = codec,
-        }),
-        .context = talloc_struct(sh, struct sd_ass_priv, {
-            .ass_track = track,
-            .vsfilter_aspect = is_ass_sub(codec),
-        }),
-        .initialized = true,
-    };
-    return sh;
-}
-
 struct ass_track *sub_get_ass_track(struct osd_state *osd)
 {
     struct sh_sub *sh = osd ? osd->sh_sub : NULL;