mmf: set channel layout

libavformat/mmf.c

@@ -18,6 +18,8 @@
  * License along with Libav; if not, write to the Free Software
  * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
  */
+
+#include "libavutil/channel_layout.h"
 #include "avformat.h"
 #include "internal.h"
 #include "avio_internal.h"
@@ -249,6 +251,7 @@ static int mmf_read_header(AVFormatContext *s)
     st->codec->codec_id = AV_CODEC_ID_ADPCM_YAMAHA;
     st->codec->sample_rate = rate;
     st->codec->channels = 1;
+    st->codec->channel_layout = AV_CH_LAYOUT_MONO;
     st->codec->bits_per_coded_sample = 4;
     st->codec->bit_rate = st->codec->sample_rate * st->codec->bits_per_coded_sample;