doc/examples/muxing: pick a supported channel layout if stereo isnt supported by the encoder

Signed-off-by: Michael Niedermayer <michaelni@gmx.at>

doc/examples/muxing.c

@@ -93,6 +93,7 @@ static void add_stream(OutputStream *ost, AVFormatContext *oc,
                        enum AVCodecID codec_id)
 {
     AVCodecContext *c;
+    int i;
 
     /* find the encoder */
     *codec = avcodec_find_encoder(codec_id);
@@ -116,8 +117,15 @@ static void add_stream(OutputStream *ost, AVFormatContext *oc,
             (*codec)->sample_fmts[0] : AV_SAMPLE_FMT_FLTP;
         c->bit_rate    = 64000;
         c->sample_rate = 44100;
-        c->channels    = 2;
         c->channel_layout = AV_CH_LAYOUT_STEREO;
+        if ((*codec)->channel_layouts) {
+            c->channel_layout = (*codec)->channel_layouts[0];
+            for (i = 0; (*codec)->channel_layouts[i]; i++) {
+                if ((*codec)->channel_layouts[i] == AV_CH_LAYOUT_STEREO)
+                    c->channel_layout = AV_CH_LAYOUT_STEREO;
+            }
+        }
+        c->channels        = av_get_channel_layout_nb_channels(c->channel_layout);
         ost->st->time_base = (AVRational){ 1, c->sample_rate };
         break;