av1/h264_metadata, filter_units: Count down when deleting units

When testing whether a particular unit should be kept or discarded, it
is best to start at the very last unit of a fragment and count down,
because that way a unit that will eventually be deleted won't be
memmoved during earlier deletions; and frag/au->nb_units need only be
evaluated once in this case and the counter is automatically correct
when a unit got deleted.

It also works for double loops, i.e. when looping over all SEI messages
in all SEI units of an access unit.

Signed-off-by: Andreas Rheinhardt <andreas.rheinhardt@gmail.com>

1 files changed, 1 insertions, 2 deletions

diff --git a/libavcodec/av1_metadata_bsf.c b/libavcodec/av1_metadata_bsf.c
index e294d7a24e..842b80c201 100644
--- a/libavcodec/av1_metadata_bsf.c
+++ b/libavcodec/av1_metadata_bsf.c
@@ -160,14 +160,13 @@ static int av1_metadata_filter(AVBSFContext *bsf, AVPacket *pkt)
     }
 
     if (ctx->delete_padding) {
-        for (i = 0; i < frag->nb_units; i++) {
+        for (i = frag->nb_units - 1; i >= 0; i--) {
             if (frag->units[i].type == AV1_OBU_PADDING) {
                 err = ff_cbs_delete_unit(ctx->cbc, frag, i);
                 if (err < 0) {
                     av_log(bsf, AV_LOG_ERROR, "Failed to delete Padding OBU.\n");
                     goto fail;
                 }
-                --i;
             }
         }
     }