avutil/channel_layout: print known layout names in custom layout

If a custom layout is equivalent to a native one, check if it matches one of the
known layout names and print that instead.

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

libavutil/channel_layout.c

@@ -679,6 +679,29 @@ int av_channel_layout_copy(AVChannelLayout *dst, const AVChannelLayout *src)
     return 0;
 }
 
+static int64_t masked_description(const AVChannelLayout *channel_layout, int start_channel)
+{
+    uint64_t mask = 0;
+    for (int i = start_channel; i < channel_layout->nb_channels; i++) {
+        enum AVChannel ch = channel_layout->u.map[i].id;
+        if (ch >= 0 && ch < 63 && mask < (1ULL << ch))
+            mask |= (1ULL << ch);
+        else
+            return AVERROR(EINVAL);
+    }
+    return mask;
+}
+
+static int has_channel_names(const AVChannelLayout *channel_layout)
+{
+    if (channel_layout->order != AV_CHANNEL_ORDER_CUSTOM)
+        return 0;
+    for (int i = 0; i < channel_layout->nb_channels; i++)
+        if (channel_layout->u.map[i].name[0])
+            return 1;
+    return 0;
+}
+
 /**
  * If the layout is n-th order standard-order ambisonic, with optional
  * extra non-diegetic channels at the end, return the order.
@@ -745,11 +768,19 @@ static int try_describe_ambisonic(AVBPrint *bp, const AVChannelLayout *channel_l
             extra.order       = AV_CHANNEL_ORDER_NATIVE;
             extra.nb_channels = av_popcount64(channel_layout->u.mask);
             extra.u.mask      = channel_layout->u.mask;
+        } else {
+            int64_t mask;
+            if (!has_channel_names(channel_layout) &&
+                (mask = masked_description(channel_layout, nb_ambi_channels)) > 0) {
+                extra.order       = AV_CHANNEL_ORDER_NATIVE;
+                extra.nb_channels = av_popcount64(mask);
+                extra.u.mask      = mask;
             } else {
                 extra.order       = AV_CHANNEL_ORDER_CUSTOM;
                 extra.nb_channels = channel_layout->nb_channels - nb_ambi_channels;
                 extra.u.map       = channel_layout->u.map + nb_ambi_channels;
             }
+        }
 
         av_bprint_chars(bp, '+', 1);
         av_channel_layout_describe_bprint(&extra, bp);
@@ -774,9 +805,17 @@ int av_channel_layout_describe_bprint(const AVChannelLayout *channel_layout,
         // fall-through
     case AV_CHANNEL_ORDER_CUSTOM:
         if (channel_layout->order == AV_CHANNEL_ORDER_CUSTOM) {
+            int64_t mask;
             int res = try_describe_ambisonic(bp, channel_layout);
             if (res >= 0)
                 return 0;
+            if (!has_channel_names(channel_layout) &&
+                (mask = masked_description(channel_layout, 0)) > 0) {
+                AVChannelLayout native = { .order       = AV_CHANNEL_ORDER_NATIVE,
+                                           .nb_channels = av_popcount64(mask),
+                                           .u.mask      = mask };
+                return av_channel_layout_describe_bprint(&native, bp);
+            }
         }
         if (channel_layout->nb_channels)
             av_bprintf(bp, "%d channels (", channel_layout->nb_channels);
@@ -1037,29 +1076,6 @@ uint64_t av_channel_layout_subset(const AVChannelLayout *channel_layout,
     return ret;
 }
 
-static int64_t masked_description(AVChannelLayout *channel_layout, int start_channel)
-{
-    uint64_t mask = 0;
-    for (int i = start_channel; i < channel_layout->nb_channels; i++) {
-        enum AVChannel ch = channel_layout->u.map[i].id;
-        if (ch >= 0 && ch < 63 && mask < (1ULL << ch))
-            mask |= (1ULL << ch);
-        else
-            return AVERROR(EINVAL);
-    }
-    return mask;
-}
-
-static int has_channel_names(AVChannelLayout *channel_layout)
-{
-    if (channel_layout->order != AV_CHANNEL_ORDER_CUSTOM)
-        return 0;
-    for (int i = 0; i < channel_layout->nb_channels; i++)
-        if (channel_layout->u.map[i].name[0])
-            return 1;
-    return 0;
-}
-
 int av_channel_layout_retype(AVChannelLayout *channel_layout, enum AVChannelOrder order, int flags)
 {
     int allow_lossy = !(flags & AV_CHANNEL_LAYOUT_RETYPE_FLAG_LOSSLESS);

tests/ref/fate/channel_layout

@@ -195,7 +195,7 @@ With "FL@Boo": CUSTOM (1 channels (FL@Boo))
 With "stereo": NATIVE (stereo)
   ~~ UNSPEC (2 channels)
   == NATIVE (stereo)
-  == CUSTOM (2 channels (FL+FR))
+  == CUSTOM (stereo)
   != AMBI
 With "FR+FL": CUSTOM (2 channels (FR+FL))
   ~~ UNSPEC (2 channels)
@@ -205,7 +205,7 @@ With "FR+FL": CUSTOM (2 channels (FR+FL))
 With "ambisonic 2+stereo": AMBI   (ambisonic 2+stereo)
   ~~ UNSPEC (11 channels)
   != NATIVE
-  == CUSTOM (ambisonic 2+2 channels (FL+FR))
+  == CUSTOM (ambisonic 2+stereo)
   == AMBI   (ambisonic 2+stereo)
 With "2C": UNSPEC (2 channels)
   == UNSPEC (2 channels)