Right now ffmpeg doesn't export a mirroring status when checking the
display matrix for rotation.
Here is an example video: https://files.tedm.io/flip.mp4
-Ted
From 7121cecdd54f403cb857dbfd056ca22253d6948a Mon Sep 17 00:00:00 2001
From: Ted Meyer <tmathme...@chromium.org>
Date: Thu, 16 May 2019 14:17:51 -0700
Subject: [PATCH 1/1] Export display matrix mirroring information
MIME-Version: 1.0
Content-Type: text/plain; charset=UTF-8
Content-Transfer-Encoding: 8bit
normally a display matrix will look like:
[ cos(Θ), -sin(Θ), ...]
[ sin(Θ), cos(Θ), ...]
[ ..., ..., ...]
but switching the signs can be used to imply a mirroring effect.
If the cosine values are of a different sign, then there is a
mirroring about the y-axis, and if the sine values are the same
sign, but non-zero, then there is a mirroring about the x-axis.
Signed-off-by: Ted Meyer <tmathme...@chromium.org>
---
libavformat/mov.c | 10 ++++++++++
1 file changed, 10 insertions(+)
diff --git a/libavformat/mov.c b/libavformat/mov.c
index e40bcf3b86..b8748ee374 100644
--- a/libavformat/mov.c
+++ b/libavformat/mov.c
@@ -4560,6 +4560,16 @@ static int mov_read_tkhd(MOVContext *c, AVIOContext *pb, MOVAtom atom)
snprintf(rotate_buf, sizeof(rotate_buf), "%g", rotate);
av_dict_set(&st->metadata, "rotate", rotate_buf, 0);
}
+
+ if (sc->display_matrix[0] != sc->display_matrix[4]) {
+ av_dict_set(&st->metadata, "mirror-y", "yes", 0);
+ }
+
+ // non-mirrored matricies have differing signs - except 0
+ if (sc->display_matrix[1] == sc->display_matrix[3] &&
+ sc->display_matrix[1] != 0) {
+ av_dict_set(&st->metadata, "mirror-x", "yes", 0);
+ }
#endif
}
--
2.21.0.1020.gf2820cf01a-goog
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