support forcing low_delay during decoding

Originally committed as revision 1150 to svn://svn.ffmpeg.org/ffmpeg/trunk

libavcodec/avcodec.h

@@ -132,6 +132,7 @@ static const int Motion_Est_QTab[] = { ME_ZERO, ME_PHODS, ME_LOG,
                                                 allows the last part of a frame to be decoded earlier */
 #define CODEC_FLAG_NORMALIZE_AQP  0x00020000 /* normalize adaptive quantization */
 #define CODEC_FLAG_INTERLACED_DCT 0x00040000 /* use interlaced dct */
+#define CODEC_FLAG_LOW_DELAY      0x00080000 /* force low delay / will fail on b frames */
 
 /* codec capabilities */
 

libavcodec/h263dec.c

@@ -351,6 +351,9 @@ retry:
         }
         ret = ff_mpeg4_decode_picture_header(s, &s->gb);
 
+        if(s->flags& CODEC_FLAG_LOW_DELAY)
+            s->low_delay=1;
+
         s->has_b_frames= !s->low_delay;
     } else if (s->h263_intel) {
         ret = intel_h263_decode_picture_header(s);