Make sure mp1/mp2 get their frame_size set.

Fixes issue1696

Originally committed as revision 21972 to svn://svn.ffmpeg.org/ffmpeg/trunk

libavformat/utils.c

@@ -1914,6 +1914,8 @@ static int has_codec_parameters(AVCodecContext *enc)
         if(!enc->frame_size &&
            (enc->codec_id == CODEC_ID_VORBIS ||
             enc->codec_id == CODEC_ID_AAC ||
+            enc->codec_id == CODEC_ID_MP1 ||
+            enc->codec_id == CODEC_ID_MP2 ||
             enc->codec_id == CODEC_ID_MP3 ||
             enc->codec_id == CODEC_ID_SPEEX))
             return 0;