[FFmpeg-devel] [PATCH 2/2] libavfilter/scale2ref: Maintain main input's DAR

[Kevin Mark]

The scale2ref filter will now maintain the DAR of the main input and
not the DAR of the reference input. This previous behavior was deemed
counterintuitive for most (all?) use-cases.

Before:
scale2ref=iw/4:ow/mdar
in  w:320 h:240 fmt:rgb24 sar:1/1
ref w:640 h:360 fmt:rgb24 sar:1/1
out w:160 h:120 fmt:rgb24 sar:4/3 flags:0x2
SAR: ((120 * 640) / (160 * 360)) * (1 / 1) = 4 / 3
DAR: (160 / 120) * (4 / 3) = 16 / 9
(main out now same DAR as ref)

Now:
scale2ref=iw/4:ow/mdar
in  w:320 h:240 fmt:rgb24 sar:1/1
ref w:640 h:360 fmt:rgb24 sar:1/1
out w:160 h:120 fmt:rgb24 sar:1/1 flags:0x2
SAR: ((120 * 320) / (160 * 240)) * (1 / 1) = 1 / 1
DAR: (160 / 120) * (1 / 1) = 4 / 3
(main out same DAR as main in)

The scale2ref FATE test has also been updated.

Signed-off-by: Kevin Mark <kmark937 at gmail.com>
---
 libavfilter/vf_scale.c                      | 6 +++---
 tests/ref/fate/filter-scale2ref_keep_aspect | 2 +-
 2 files changed, 4 insertions(+), 4 deletions(-)

diff --git a/libavfilter/vf_scale.c b/libavfilter/vf_scale.c
index 9232bc4439..5e55f9344b 100644
--- a/libavfilter/vf_scale.c
+++ b/libavfilter/vf_scale.c
@@ -337,10 +337,10 @@ static int config_props(AVFilterLink *outlink)
         }
     }
 
-    if (inlink->sample_aspect_ratio.num){
-        outlink->sample_aspect_ratio = av_mul_q((AVRational){outlink->h * inlink->w, outlink->w * inlink->h}, inlink->sample_aspect_ratio);
+    if (inlink0->sample_aspect_ratio.num){
+        outlink->sample_aspect_ratio = av_mul_q((AVRational){outlink->h * inlink0->w, outlink->w * inlink0->h}, inlink0->sample_aspect_ratio);
     } else
-        outlink->sample_aspect_ratio = inlink->sample_aspect_ratio;
+        outlink->sample_aspect_ratio = inlink0->sample_aspect_ratio;
 
     if (ctx->filter == &ff_vf_scale2ref) {
         av_log(ctx, AV_LOG_VERBOSE, "in  w:%d h:%d fmt:%s sar:%d/%d\n",
diff --git a/tests/ref/fate/filter-scale2ref_keep_aspect b/tests/ref/fate/filter-scale2ref_keep_aspect
index ca03277446..8dd0dbb13b 100644
--- a/tests/ref/fate/filter-scale2ref_keep_aspect
+++ b/tests/ref/fate/filter-scale2ref_keep_aspect
@@ -5,7 +5,7 @@
 #media_type 0: video
 #codec_id 0: rawvideo
 #dimensions 0: 160x120
-#sar 0: 4/3
+#sar 0: 1/1
 #stream#, dts,        pts, duration,     size, hash
 0,          0,          0,        1,    57600, 9a19c23dc3a557786840d0098606d5f1
 0,          1,          1,        1,    57600, e6fbdabaf1bb0d28afc648ed4d27e9f0
-- 
2.13.0