cleanup

adding AVVideoFrame
 moving quality, pict_type, key_frame, qscale_table, ... to AVVideoFrame
 removing obsolete variables in AVCodecContext
 skiping of MBs in b frames
 correctly initalizing AVCodecContext
 picture buffer cleanup

Originally committed as revision 1302 to svn://svn.ffmpeg.org/ffmpeg/trunk

libavformat/jpeg.c

@@ -170,6 +170,8 @@ static int jpeg_read_header(AVFormatContext *s1, AVFormatParameters *ap)
         av_free(s);
         return -ENOMEM;
     }
+    avcodec_get_context_defaults(&st->codec);
+
     s1->streams[0] = st;
     s->img_number = 0;