MXF files lose metadata upon copy/remux

[brtstyczen]

If an MXF file has reel_name stored in a stream, while copying or
remuxing file, some (most) of the stream metadata is lost.
Here’s the file:
​https://streams.videolan.org/ffmpeg/incoming/original.mxf

After running ffmpeg -i original.mxf -c copy output.mxf, and checking
with ffprobe,
the original file has the following stream metadata:

file_package_umid:
0x060A2B340101010501010D431300000064F640280FA57031060E2B347F7F2A80
      file_package_name: B002C0006_230803_1932_000001 (0)
      track_name      : B002C0006_230803_1932_000001 (0)_v1
      reel_umid       :
0x060A2B340101010501010D431300000064F640280FA67031060E2B347F7F2A80
      reel_name       : B002C0006_230803_1932_000001 (1)
      timecode        : 00:06:15:21

And the copied file only these:

file_package_umid:
0x060A2B340101010501010D001339242252947134203924220052947134203901
      file_package_name: B002C0006_230803_1932_000001 (0)

After applying the patch, copied file correctly shows reel metadata
and the timecode:

 file_package_umid:
0x060A2B340101010501010D001321CA09529471342721CA090052947134272101
      file_package_name: B002C0006_230803_1932_000001 (0)
      reel_umid       :
0x060A2B340101010501010D001321CA09529471342721CA090052947134272102
      reel_name       : B002C0006_230803_1932_000001 (1)
      timecode        : 00:06:15:21

The track_name is still missing though, so I will continue to
investigate the issue.

Proposed patch:

Signed-off-by: Bart Styczen <bart.styczen@cine.dev>
---
libavformat/mxfenc.c | 12 +++++++++++-
1 file changed, 11 insertions(+), 1 deletion(-)

diff --git a/libavformat/mxfenc.c b/libavformat/mxfenc.c
index d8252ed68f..d3ae83a9fb 100644
--- a/libavformat/mxfenc.c
+++ b/libavformat/mxfenc.c
@@ -1817,7 +1817,17 @@ static int mxf_write_header_metadata_sets(AVFormatContext *s)
    }

    entry = av_dict_get(s->metadata, "reel_name", NULL, 0);
-    if (entry) {
+    if (!entry) {
+        /* check if any of the streams contain a reel_name */
+        for (i = 0; i < s->nb_streams; i++) {
+            st = s->streams[i];
+            if (entry = av_dict_get(st->metadata, "reel_name", NULL, 0)) {
+                break;
+            }
+        }
+    }
+    
+    if (entry) {
        packages[2].name = entry->value;
        packages[2].type = SourcePackage;
        packages[2].instance = 2;
--
2.37.1 (Apple Git-137.1)