[FFmpeg-devel] [PATCH v2] avformat/mov: Properly consider if the file is self-initializing when marking sidx reading complete

[Derek Buitenhuis]

Files with the "dash" major brand are guaranteed to only have a single
initialization range for the whole file. We can check this and stop
appropriately - which is useful, as the existing check to see if the
offset reaches the end of the file is not sufficient. For example,
Premiere creates valid self-initializing ISOBMFF files that contain
a single 'uuid' box appended at the end, after the last 'moof', and
this check does not catch that, which causes, for example, probing
to traverse the entire file (every single 'moof'), which is extremely
slow over a network, which is the main place these self-initializing
fragmented ISOBMFF files would be used. This is the same behavior that
was addressed in 2ff3c466eca66bb8eb32bb41a4ce70fe285e3ea0 for live-style
fragmented files.

Signed-off-by: Derek Buitenhuis <derek.buitenhuis at gmail.com>
---
Updated the commit message too, to reflect that the files are actually
a YouTube-muxed file that was opened in Premiere, which appends XMP
metadata in a 'uuid' box to files it opens. Gross.
---
 libavformat/mov.c | 10 +++++++++-
 1 file changed, 9 insertions(+), 1 deletion(-)

diff --git a/libavformat/mov.c b/libavformat/mov.c
index 23b0ead01e..0eb52ab6e6 100644
--- a/libavformat/mov.c
+++ b/libavformat/mov.c
@@ -5052,6 +5052,8 @@ static int mov_read_sidx(MOVContext *c, AVIOContext *pb, MOVAtom atom)
     AVStream *ref_st = NULL;
     MOVStreamContext *sc, *ref_sc = NULL;
     AVRational timescale;
+    AVDictionaryEntry *major_brand = av_dict_get(c->fc->metadata, "major_brand", NULL, AV_DICT_MATCH_CASE);
+    AVDictionaryEntry *compatible_brands = av_dict_get(c->fc->metadata, "compatible_brands", NULL, AV_DICT_MATCH_CASE);
 
     version = avio_r8(pb);
     if (version > 1) {
@@ -5120,7 +5122,13 @@ static int mov_read_sidx(MOVContext *c, AVIOContext *pb, MOVAtom atom)
     sc->has_sidx = 1;
 
     // See if the remaining bytes are just an mfra which we can ignore.
-    is_complete = offset == stream_size;
+    //
+    // Also check to see if the file is Self-initializing, which guarantees
+    // only a single initialization range is present for the whole file.
+    // See: ISO-IEC 23009-1 Section 6.3.5.
+    is_complete = offset == stream_size ||
+                  (major_brand && !strncmp(major_brand->value, "dash", 4)) ||
+                  (compatible_brands && strstr(compatible_brands->value, "dash"));
     if (!is_complete && (pb->seekable & AVIO_SEEKABLE_NORMAL)) {
         int64_t ret;
         int64_t original_pos = avio_tell(pb);
-- 
2.30.0