Check sample_aspect_ratio validity for mpeg4/h263/h263p encoding.

Merged from ffmbc0.3

Originally committed as revision 20861 to svn://svn.ffmpeg.org/ffmpeg/trunk

libavcodec/mpegvideo_enc.c

@@ -395,6 +395,14 @@ av_cold int MPV_encode_init(AVCodecContext *avctx)
         return -1;
     }
 
+    if ((s->codec_id == CODEC_ID_MPEG4 || s->codec_id == CODEC_ID_H263 ||
+         s->codec_id == CODEC_ID_H263P) &&
+        (avctx->sample_aspect_ratio.num > 255 || avctx->sample_aspect_ratio.den > 255)) {
+        av_log(avctx, AV_LOG_ERROR, "Invalid pixel aspect ratio %i/%i, limit is 255/255\n",
+               avctx->sample_aspect_ratio.num, avctx->sample_aspect_ratio.den);
+        return -1;
+    }
+
     if((s->flags & (CODEC_FLAG_INTERLACED_DCT|CODEC_FLAG_INTERLACED_ME|CODEC_FLAG_ALT_SCAN))
        && s->codec_id != CODEC_ID_MPEG4 && s->codec_id != CODEC_ID_MPEG2VIDEO){
         av_log(avctx, AV_LOG_ERROR, "interlacing not supported by codec\n");