PATCH by Rik Snel <rsnel@cube.dyndns.org>

this patch enhances the jpeg header writer. It can be asked to omit
quantisation and huffman tables and it can write different horizontal and
vertical sampling factors. (the last thing is useless for libavcodec
itself (because libavcodec only handles YUV420P at ecoder level), but the
values are initialized so that operation of libavcodec is not impaired)

Originally committed as revision 290 to svn://svn.ffmpeg.org/ffmpeg/trunk

libavcodec/mjpeg.c

@@ -259,7 +259,7 @@ void mjpeg_picture_header(MpegEncContext *s)
 {
     put_marker(&s->pb, SOI);
 
-    jpeg_table_header(s);
+    if (s->mjpeg_write_tables) jpeg_table_header(s);
 
     put_marker(&s->pb, SOF0);
 
@@ -271,20 +271,20 @@ void mjpeg_picture_header(MpegEncContext *s)
     
     /* Y component */
     put_bits(&s->pb, 8, 1); /* component number */
-    put_bits(&s->pb, 4, 2); /* H factor */
-    put_bits(&s->pb, 4, 2); /* V factor */
+    put_bits(&s->pb, 4, s->mjpeg_hsample[0]); /* H factor */
+    put_bits(&s->pb, 4, s->mjpeg_vsample[0]); /* V factor */
     put_bits(&s->pb, 8, 0); /* select matrix */
     
     /* Cb component */
     put_bits(&s->pb, 8, 2); /* component number */
-    put_bits(&s->pb, 4, 1); /* H factor */
-    put_bits(&s->pb, 4, 1); /* V factor */
+    put_bits(&s->pb, 4, s->mjpeg_hsample[1]); /* H factor */
+    put_bits(&s->pb, 4, s->mjpeg_vsample[1]); /* V factor */
     put_bits(&s->pb, 8, 0); /* select matrix */
 
     /* Cr component */
     put_bits(&s->pb, 8, 3); /* component number */
-    put_bits(&s->pb, 4, 1); /* H factor */
-    put_bits(&s->pb, 4, 1); /* V factor */
+    put_bits(&s->pb, 4, s->mjpeg_hsample[2]); /* H factor */
+    put_bits(&s->pb, 4, s->mjpeg_vsample[2]); /* V factor */
     put_bits(&s->pb, 8, 0); /* select matrix */
 
     /* scan header */

libavcodec/mpegvideo.c

@@ -283,6 +283,13 @@ int MPV_encode_init(AVCodecContext *avctx)
     case CODEC_ID_MJPEG:
         s->out_format = FMT_MJPEG;
         s->intra_only = 1; /* force intra only for jpeg */
+	s->mjpeg_write_tables = 1; /* write all tables */
+	s->mjpeg_vsample[0] = 2; /* set up default sampling factors */
+	s->mjpeg_vsample[1] = 1; /* the only currently supported values */
+	s->mjpeg_vsample[2] = 1; 
+	s->mjpeg_hsample[0] = 2; 
+	s->mjpeg_hsample[1] = 1; 
+	s->mjpeg_hsample[2] = 1; 
         if (mjpeg_init(s) < 0)
             return -1;
         break;

libavcodec/mpegvideo.h

@@ -157,6 +157,10 @@ typedef struct MpegEncContext {
     
     /* MJPEG specific */
     struct MJpegContext *mjpeg_ctx;
+    int mjpeg_vsample[3]; /* vertical sampling factors, default = {2, 1, 1} */
+    int mjpeg_hsample[3]; /* horizontal sampling factors, default = {2, 1, 1} */
+    int mjpeg_write_tables; /* do we want to have quantisation- and
+			       huffmantables in the jpeg file ? */
 
     /* MSMPEG4 specific */
     int mv_table_index;