commit 98faa17f139b1c280fbea40563078b1fcb438aa5
author Vignesh Venkatasubramanian <vigneshv@google.com> Mon Sep 19 13:50:23 2022 -0700
committer Vignesh Venkatasubramanian <vigneshvg@users.noreply.github.com> Tue Sep 20 15:33:42 2022 -0700
tree 102e0717c6ebdacfedef01b9fc1661eb41dac3b1
parent 815f7c6ae41c426a300ed9085f5f2480f6199ab4

Write 'auxi' box for animated images with alpha channel

When alpha channel is present on animated images, the 'auxi' box is
mandatory as it tells the decoder what kind of auxiliary track it
is.

The current decoder gets the value from the still image item
properties. But if a decoder ignores the still image fields and
treats the animated AVIF as a video sequence, it has no way of
knowing what kind of information the auxiliary track contains.

This patch resolves the following compliance warden error:
[heif][Rule #1] Section 7.5.3.1
The nature of the auxiliary track is announced by the AuxiliaryTypeInfoBox that
shall be included in the sample entry of the auxiliary track.

src/write.c

diff --git a/src/write.c b/src/write.c
index 8f0bb30..e25e112 100644
--- a/src/write.c
+++ b/src/write.c
@@ -1589,6 +1589,12 @@
             avifRWStreamWriteZeros(&s, 3); // unsigned int(26) reserved; (two zero bits are written along with ccstValue).
             avifRWStreamFinishBox(&s, ccst);
 
+            if (item->alpha) {
+                avifBoxMarker auxi = avifRWStreamWriteFullBox(&s, "auxi", AVIF_BOX_SIZE_TBD, 0, 0);
+                avifRWStreamWriteChars(&s, alphaURN, alphaURNSize); //  string aux_track_type;
+                avifRWStreamFinishBox(&s, auxi);
+            }
+
             avifRWStreamFinishBox(&s, av01);
             avifRWStreamFinishBox(&s, stsd);