Document h263_get_picture_format().

Originally committed as revision 21043 to svn://svn.ffmpeg.org/ffmpeg/trunk

libavcodec/mpegvideo.h

@@ -839,7 +839,14 @@ int ff_h263_decode_mb(MpegEncContext *s,
                       DCTELEM block[6][64]);
 int ff_mpeg4_decode_mb(MpegEncContext *s,
                       DCTELEM block[6][64]);
+
+/**
+ * Returns the value of the 3bit "source format" syntax element.
+ * that represents some standard picture dimensions or indicates that
+ * width&height are explicitly stored later.
+ */
 int h263_get_picture_format(int width, int height);
+
 void ff_mpeg4_encode_video_packet_header(MpegEncContext *s);
 void ff_mpeg4_clean_buffers(MpegEncContext *s);
 void ff_mpeg4_stuffing(PutBitContext * pbc);