forbid mp3 < 16000hz in anything except mov

Originally committed as revision 15189 to svn://svn.ffmpeg.org/ffmpeg/trunk

libavformat/movenc.c

@@ -1610,6 +1610,12 @@ static int mov_write_header(AVFormatContext *s)
             }else{
                 track->sampleSize = (av_get_bits_per_sample(st->codec->codec_id) >> 3) * st->codec->channels;
             }
+            if(track->mode != MODE_MOV &&
+               track->enc->codec_id == CODEC_ID_MP3 && track->enc->sample_rate < 16000){
+                av_log(s, AV_LOG_ERROR, "track %d: muxing mp3 at %dhz is not supported\n",
+                       i, track->enc->sample_rate);
+                return -1;
+            }
         }
     }