mov: Add an option to toggle dref opening

This feature is mostly only used by NLE software, and is
both of dubious value being enabled by default, and a
possible security risk.
Signed-off-by: Derek Buitenhuis <derek.buitenhuis@gmail.com>
Signed-off-by: Michael Niedermayer <michael@niedermayer.cc>
(cherry picked from commit 712d962a)

Conflicts:

	libavformat/isom.h
	libavformat/mov.c
	libavformat/version.h
Signed-off-by: Michael Niedermayer <michael@niedermayer.cc>

libavformat/isom.h

@@ -209,6 +209,7 @@ typedef struct MOVContext {
     void *audible_fixed_key;
     int audible_fixed_key_size;
     struct AVAES *aes_decrypt;
+    int enable_drefs;
 } MOVContext;
 
 int ff_mp4_read_descr_len(AVIOContext *pb);

libavformat/mov.c

@@ -3002,13 +3002,23 @@ static int mov_read_trak(MOVContext *c, AVIOContext *pb, MOVAtom atom)
 
     if (sc->dref_id-1 < sc->drefs_count && sc->drefs[sc->dref_id-1].path) {
         MOVDref *dref = &sc->drefs[sc->dref_id - 1];
-        if (mov_open_dref(c, &sc->pb, c->fc->filename, dref,
-                          &c->fc->interrupt_callback) < 0)
-            av_log(c->fc, AV_LOG_ERROR,
-                   "stream %d, error opening alias: path='%s', dir='%s', "
-                   "filename='%s', volume='%s', nlvl_from=%d, nlvl_to=%d\n",
+        if (c->enable_drefs) {
+            if (mov_open_dref(c, &sc->pb, c->fc->filename, dref,
+                              &c->fc->interrupt_callback) < 0)
+                av_log(c->fc, AV_LOG_ERROR,
+                       "stream %d, error opening alias: path='%s', dir='%s', "
+                       "filename='%s', volume='%s', nlvl_from=%d, nlvl_to=%d\n",
+                       st->index, dref->path, dref->dir, dref->filename,
+                       dref->volume, dref->nlvl_from, dref->nlvl_to);
+        } else {
+            av_log(c->fc, AV_LOG_WARNING,
+                   "Skipped opening external track: "
+                   "stream %d, alias: path='%s', dir='%s', "
+                   "filename='%s', volume='%s', nlvl_from=%d, nlvl_to=%d."
+                   "Set enable_drefs to allow this.\n",
                    st->index, dref->path, dref->dir, dref->filename,
                    dref->volume, dref->nlvl_from, dref->nlvl_to);
+        }
     } else {
         sc->pb = c->fc->pb;
         sc->pb_is_copied = 1;
@@ -4925,6 +4935,8 @@ static const AVOption mov_options[] = {
         "Fixed key used for handling Audible AAX files", OFFSET(audible_fixed_key),
         AV_OPT_TYPE_BINARY, {.str="77214d4b196a87cd520045fd20a51d67"},
         .flags = AV_OPT_FLAG_DECODING_PARAM },
+    { "enable_drefs", "Enable external track support.", OFFSET(enable_drefs), AV_OPT_TYPE_INT,
+        {.i64 = 0}, 0, 1, FLAGS },
     { NULL },
 };