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 712d962a6a)

Conflicts:

	libavformat/isom.h
	libavformat/mov.c
	libavformat/version.h

Signed-off-by: Michael Niedermayer <michael@niedermayer.cc>

libavformat/isom.h

@@ -172,6 +172,7 @@ typedef struct MOVContext {
     int bitrates_count;
     int moov_retry;
     int atom_depth;
+    int enable_drefs;
 } MOVContext;
 
 int ff_mp4_read_descr_len(AVIOContext *pb);

libavformat/mov.c

@@ -2465,13 +2465,23 @@ 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(&sc->pb, c->fc->filename, dref, &c->fc->interrupt_callback,
-            c->use_absolute_path, c->fc) < 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(&sc->pb, c->fc->filename, dref, &c->fc->interrupt_callback,
+                              c->use_absolute_path, c->fc) < 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;
@@ -3904,6 +3914,8 @@ static int mov_read_seek(AVFormatContext *s, int stream_index, int64_t sample_ti
     return 0;
 }
 
+#define OFFSET(x) offsetof(MOVContext, x)
+#define FLAGS AV_OPT_FLAG_VIDEO_PARAM | AV_OPT_FLAG_DECODING_PARAM
 static const AVOption options[] = {
     {"use_absolute_path",
         "allow using absolute path when opening alias, this is a possible security issue",
@@ -3911,6 +3923,8 @@ static const AVOption options[] = {
         0, 1, AV_OPT_FLAG_VIDEO_PARAM|AV_OPT_FLAG_DECODING_PARAM},
     {"ignore_editlist", "", offsetof(MOVContext, ignore_editlist), FF_OPT_TYPE_INT, {.i64 = 0},
         0, 1, AV_OPT_FLAG_VIDEO_PARAM|AV_OPT_FLAG_DECODING_PARAM},
+    { "enable_drefs", "Enable external track support.", OFFSET(enable_drefs), AV_OPT_TYPE_INT,
+        {.i64 = 0}, 0, 1, FLAGS },
     {NULL}
 };