avformat/movenc: ensure we don't write the major brand as a compatible brand more than once

Signed-off-by: James Almer <jamrial@gmail.com>

1 files changed, 22 insertions, 10 deletions

diff --git a/libavformat/movenc.c b/libavformat/movenc.c
index c13578e13f..907d0a049f 100644
--- a/libavformat/movenc.c
+++ b/libavformat/movenc.c
@@ -4801,20 +4801,32 @@ static int mov_write_ftyp_tag(AVIOContext *pb, AVFormatContext *s)
     // Write the major brand as the first compatible brand as well
     mov_write_ftyp_tag_internal(pb, s, has_h264, has_video, 0);
 
+    // Write compatible brands, ensuring that we don't write the major brand as a
+    // compatible brand a second time.
     if (mov->mode == MODE_ISM) {
         ffio_wfourcc(pb, "piff");
-    } else if (!(mov->flags & FF_MOV_FLAG_DEFAULT_BASE_MOOF)) {
-        ffio_wfourcc(pb, "isom");
-        ffio_wfourcc(pb, "iso2");
-        if (has_h264)
-            ffio_wfourcc(pb, "avc1");
+    } else if (mov->mode != MODE_MOV) {
+        // We add tfdt atoms when fragmenting, signal this with the iso6 compatible
+        // brand. This is compatible with users that don't understand tfdt.
+        if (mov->flags & FF_MOV_FLAG_FRAGMENT)
+            ffio_wfourcc(pb, "iso6");
+        if (mov->mode != MODE_MP4) {
+            if (mov->flags & FF_MOV_FLAG_DEFAULT_BASE_MOOF)
+                ffio_wfourcc(pb, "iso5");
+            else if (mov->flags & FF_MOV_FLAG_NEGATIVE_CTS_OFFSETS)
+                ffio_wfourcc(pb, "iso4");
+        }
+        // Brands prior to iso5 can't be signaled when using default-base-is-moof
+        if (!(mov->flags & FF_MOV_FLAG_DEFAULT_BASE_MOOF)) {
+            // write isom for mp4 only if it it's not the major brand already.
+            if (mov->mode != MODE_MP4 || mov->flags & FF_MOV_FLAG_NEGATIVE_CTS_OFFSETS)
+                ffio_wfourcc(pb, "isom");
+            ffio_wfourcc(pb, "iso2");
+            if (has_h264)
+                ffio_wfourcc(pb, "avc1");
+        }
     }
 
-    // We add tfdt atoms when fragmenting, signal this with the iso6 compatible
-    // brand. This is compatible with users that don't understand tfdt.
-    if (mov->flags & FF_MOV_FLAG_FRAGMENT && mov->mode != MODE_ISM)
-        ffio_wfourcc(pb, "iso6");
-
     if (mov->mode == MODE_MP4)
         ffio_wfourcc(pb, "mp41");