lavf/movenc: Use a dynamic buffer when writing the mfra box

When doing streamed output, with e.g. +dash, if the mfra box ended
up being larger than the AVIOContext write buffer, the (unchecked)
seeking back to update the box size would silently fail and produce
an invalid mfra box.

This is similar to how other boxes are written in fragmented mode.

Signed-off-by: Derek Buitenhuis <derek.buitenhuis@gmail.com>

diff --git a/libavformat/movenc.c b/libavformat/movenc.c
index b8e45760ee9fd43092f94a7238da765948baec48..7db2e2884077b215c07b0656168c75d63f0e5011 100644 (file)
--- a/libavformat/movenc.c
+++ b/libavformat/movenc.c
@@ -4798,28 +4798,40 @@ static int mov_write_tfra_tag(AVIOContext *pb, MOVTrack *track)
 
 static int mov_write_mfra_tag(AVIOContext *pb, MOVMuxContext *mov)
 {
-    int64_t pos = avio_tell(pb);
-    int i;
+    AVIOContext *mfra_pb;
+    int i, ret, sz;
+    uint8_t *buf;
 
-    avio_wb32(pb, 0); /* size placeholder */
-    ffio_wfourcc(pb, "mfra");
+    ret = avio_open_dyn_buf(&mfra_pb);
+    if (ret < 0)
+        return ret;
+
+    avio_wb32(mfra_pb, 0); /* size placeholder */
+    ffio_wfourcc(mfra_pb, "mfra");
     /* An empty mfra atom is enough to indicate to the publishing point that
      * the stream has ended. */
     if (mov->flags & FF_MOV_FLAG_ISML)
-        return update_size(pb, pos);
+        goto done_mfra;
 
     for (i = 0; i < mov->nb_streams; i++) {
         MOVTrack *track = &mov->tracks[i];
         if (track->nb_frag_info)
-            mov_write_tfra_tag(pb, track);
+            mov_write_tfra_tag(mfra_pb, track);
     }
 
-    avio_wb32(pb, 16);
-    ffio_wfourcc(pb, "mfro");
-    avio_wb32(pb, 0); /* version + flags */
-    avio_wb32(pb, avio_tell(pb) + 4 - pos);
+    avio_wb32(mfra_pb, 16);
+    ffio_wfourcc(mfra_pb, "mfro");
+    avio_wb32(mfra_pb, 0); /* version + flags */
+    avio_wb32(mfra_pb, avio_tell(mfra_pb) + 4);
 
-    return update_size(pb, pos);
+done_mfra:
+
+    sz  = update_size(mfra_pb, 0);
+    ret = avio_get_dyn_buf(mfra_pb, &buf);
+    avio_write(pb, buf, ret);
+    ffio_free_dyn_buf(&mfra_pb);
+
+    return sz;
 }
 
 static int mov_write_mdat_tag(AVIOContext *pb, MOVMuxContext *mov)
@@ -6987,7 +6999,9 @@ static int mov_write_trailer(AVFormatContext *s)
         }
         if (!(mov->flags & FF_MOV_FLAG_SKIP_TRAILER)) {
             avio_write_marker(s->pb, AV_NOPTS_VALUE, AVIO_DATA_MARKER_TRAILER);
-            mov_write_mfra_tag(pb, mov);
+            res = mov_write_mfra_tag(pb, mov);
+            if (res < 0)
+                return res;
         }
     }