Make ffmpeg warns the user when the selected sample format is ignored.

Signed-off-by: Mans Rullgard <mans@mansr.com>

ffmpeg.c

@@ -600,9 +600,15 @@ static void choose_sample_fmt(AVStream *st, AVCodec *codec)
             if(*p == st->codec->sample_fmt)
                 break;
         }
-        if(*p == -1)
+        if (*p == -1) {
+            av_log(NULL, AV_LOG_WARNING,
+                   "Incompatible sample format '%s' for codec '%s', auto-selecting format '%s'\n",
+                   av_get_sample_fmt_name(st->codec->sample_fmt),
+                   codec->name,
+                   av_get_sample_fmt_name(codec->sample_fmts[0]));
             st->codec->sample_fmt = codec->sample_fmts[0];
         }
+    }
 }
 
 static void choose_sample_rate(AVStream *st, AVCodec *codec)