for (i = j = 0; i < b->nb_channel_layouts; i++)
if (KNOWN(b->channel_layouts[i]))
b->channel_layouts[j++] = b->channel_layouts[i];
+ /* Not optimal: the unknown layouts of b may become known after
+ another merge. */
+ if (!j)
+ return NULL;
b->nb_channel_layouts = j;
}
MERGE_REF(b, a, channel_layouts, AVFilterChannelLayouts, fail);