set low_delay on encoding if no b frames

Originally committed as revision 1007 to svn://svn.ffmpeg.org/ffmpeg/trunk

libavcodec/mpegvideo.c

@@ -596,7 +596,7 @@ int MPV_encode_init(AVCodecContext *avctx)
         s->h263_pred = 1;
         s->unrestricted_mv = 1;
         s->has_b_frames= s->max_b_frames ? 1 : 0;
-        s->low_delay=0;
+        s->low_delay= !s->has_b_frames;
         avctx->delay= s->low_delay ? 0 : (s->max_b_frames + 1); 
         break;
     case CODEC_ID_MSMPEG4V1:

tests/ffmpeg.regression.ref

@@ -9,12 +9,12 @@ ffmpeg regression test
 3ed8e11a8a8147c3e7d736593fccae79 *./data/out.yuv
 abe11239875a32f00fa2910828bba4fb *./data/a-h263.avi
 c1f6c8ee7a24d8345deddf1a24ca3756 *./data/out.yuv
-440192aca11c310e01168ec24ea7807e *./data/a-odivx.avi
-145c98a175e760f8ba1997edf15b2964 *./data/out.yuv
+8e41ac530894eaf3ecdb583d6d66c392 *./data/a-odivx.avi
+bf3be8fb78a9ca91dd6b252d48ce59bb *./data/out.yuv
 850ba6da4c9dad60b6719b0b06b204de *./data/a-mpeg4-rc.avi
 0ab0a58082e485478f9feab5ccc6fc42 *./data/out.yuv
-f5f44dad09c2d4d16524e539645f693c *./data/a-mpeg4-adv.avi
-d0f077a3b42367d7432b73c0ddad7438 *./data/out.yuv
+685812396445ac5c79f345965dca6b09 *./data/a-mpeg4-adv.avi
+1d6c3ba2b096ac6df63f1dcabe3ed603 *./data/out.yuv
 2846c8e3d97d7395eb746bfce44e0443 *./data/a-mjpeg.avi
 278033451d7a6bfeb8339abbe4228499 *./data/out.yuv
 ccbf683d781fa3cdfa18b618731fc74b *./data/a-rv10.rm